Hypervalent Silicon In Organic Chemistry - 東京大学
Hypervalent Silicon in Organic ChemistryLLLSiRLLRSiLLLLLiterature SeminarJanuary 5, 2013Taisuke Itoh (B4)LLSiLLRL
Hypervalent Silicion in Organic ChemistryIntroductionCatalytic Enantioselective Aldol Reaction to KetonesOSiCl3 PhOMeOHcatalyst1 (10 mol%)OCH2Cl2, -20 CMeMePhOOMe96% yield83% eet-BuN N O- -OOBuBuOt-Bucatalyst1Denmark, S. E.; Fan, Y. J. Am. Chem. Soc. 2002, 124, 4233.Enantioselective Passerini-Type ReactionOPh t-BuNCSiCl4 (1.5 equiv)catalyst (5 mol%)i-Pr2EtN (10 mol%)CH2Cl2, -74 C, 4.5 h;then sat. aq. NaHCO3HMePNNMe Mecatalyst2PhNHt-BuO93% yield93% eeThe first catalytic asymmetric !addition of isocyanides.Denmark, S. E.; Fan, Y. J. Am. Chem. Soc. 2003, 125, 7825.Denmark, S. E.; Fan, Y. J. Org. Chem. 2005, 70, 9667.ONOH2
Hypervalent Silicon in Organic ChemistryContents Structure and Property of Hypervalent SiliconHydrosililation as a Hypervalent Silicon ExampleLewis Base Catalyzed AllylsilylationDenmark’s Contribution to Lewis Base CatalyzedAldol Reaction and Allylsilylation Other Examples of Hypervalent SiliconNucleophilicity Hypervalent Silicon as a Chiral Lewis Acid
Hypervalent Silicion in Organic ChemistryStructure and Property of Hypervalent SiliconStructure and Property of Hypervalent SiliconLLLSiRLLTetravalent SiliconTetrahedralWeak Lewis AcidLow NucleophilicityRSiLLLLSiLRLLLLPentavalent SiliconTrigonal bipyramidalStrong Lewis AcidHigh NucleophilicityPentavalent SiliconOctahedralNo Lewis AcidityFurther High NucleophilicityL negatively charged or neutal silaphilic ligandssuch as F, Cl, OR and OAr or Lewis basesR H or C! at silicon!- at ligands L and RLewis aciditynucleophilicity of RRendler, S.; Qestreich, M.; Synthesis 2005, 11, 1727.
Hypervalent Silicion in Organic ChemistryStructure and Property of Hypervalent SiliconThe Moleculer Orbital of Pentavalent Silicon (Trigonal bipyramidal)ddpd!E onablepsp2sp2ssp2dpsp2pOlder models for explaining hypervalency invoked d orbitals. However, quantum chemical calculations suggest thatd-orbital participation is negligible due to the large energy difference between the relevant p and d orbitals.LR Si LLLPentavalent siliconTrigonal bipyramidalHow does sp2p moleculer orbital engage in hypervalent bonding?Magnusson, E. J. Am. Chem. Soc. 1990, 112, 7940.
Hypervalent Silicion in Organic ChemistryStructure and Property of Hypervalent SiliconThe Moleculer Orbital of Pentavalent Silicon (Trigonal bipyramidal)dThree-center four-electron bondingdAntibonding!E 200kcal/molrehybridaze3c-4e bondingppNon-Bondingsp2Bondingssp2pLSiL The filled non-bonding molecular orbital has all of the electron density on the ligand atoms. Thus, highly electronegative atoms stabilize 3c-4e bonding and hypervalent molecules andelectron density of axial position is higher than that of equatrial position. This is why most hypervalent molecules have F, Cl or OR in ligand atoms. Consequently, hypervalent molecules get more Lewis acidic.Ramsden, C. A. Chem. Soc. Rev. 1994, 23, 111.
Hypervalent Silicion in Organic ChemistryStructure and Property of Hypervalent SiliconHow do we have access to hypervalent silicon?Electronegative LigandsBent's rule : Atomic p character tendsto concentrate in orbitals that aredirected toward electronegative groups.LSiRLLTetravalent siliconRather strong Lewis acidbecause of electronegative ligands.LRLLLL : Electronegative ligandSiLPentavalent siliconStabilized by electronegative ligandsStrong Lewis acidStrain ReleaseBond angle : eq-ax 90 Bond angle 90 : Longer Si-X andSi-Y bond than C-X and C-Y bond.XYSiLRTetravalent siliconStrain release Lewis acidityXYLSiLRLPentavalent siliconStrain releasedStrong Lewis acid
Hypervalent Silicon in Organic ChemistryContents Structure and Property of Hypervalent SiliconHydrosililation as a Hypervalent Silicon ExampleLewis Base Catalyzed AllylsilylationDenmark’s Contribution to Lewis Base CatalyzedAldol Reaction and Allylsilylation Other Examples of Hypervalent SiliconNucleophilicity Hypervalent Silicon as a Chiral Lewis Acid
Hypervalent Silicion in Organic ChemistryHydrosilylation as a Hypervalent Silicon ExampleFirst Lewis Base Catalyzed Hydrosilylation(EtO)3SiH (1 eq.)CsF (1 eq.)OPhOHneat, 0 CMePhMe80%Boyer, J.; Corriu, R. J. P.; Perz, C. Tetrahedron, 1981, 37, 2165.Probable reaction mechanismHEtOCsFOEtOEtTetravalent siliconWeak Lewis acidPhMeHEtO Si OEtHEtO Si OEtOEtFPentavalent siliconStabilized by electronegative atomsStrong Lewis acidTetravalent siliconRather strong Lewis acid dueto electronegative atomsOFCsEtOOEtSiEtOOHPhMeHexavalent silliconGood hydride donorCsFOEt CsEtO Si OEtOFPhMework-upOHPhMe
Hypervalent Silicion in Organic ChemistryHydrosilylation as a Hypervalent Silicon ExampleChiral Lewis Base Catalyzed Assymetric Hydrosilylation(MeO)3SiH (1.5 eq.)Catalyst (0.4 mol%)OPhOHTHF, r.t.MePhMe89%,yield52% eeNLiOLiCatalystKohra, S.; Hayashida, H.; Tominaga, Y.; Hosomi, A. Tetrahedron Lett, 1988, 29, 89.Probable reaction mechanismHMeOOCatalystOPentavalent siliconStrong Lewis acidLiNOMeSiMeOOHMePhHexavalent silliconGood hydride donorLiN Si OMeOMeHTetravalent siliconStrain release Lewis acidityOMeON Si OMeHOMeOMeTetravalent siliconWeak Lewis acidPhStrainreleaseOHPhMe
Hypervalent Silicon in Organic ChemistryContents Structure and Property of Hypervalent SiliconHydrosililation as a Hypervalent Silicon ExampleLewis Base Catalyzed AllylsilylationDenmark’s Contribution to Lewis Base CatalyzedAldol Reaction and Allylsilylation Other Examples of Hypervalent SiliconNucleophilicity Hypervalent Silicon as a Chiral Lewis Acid
Hypervalent Silicion in Organic ChemistryLewis Base Mediated Allylation via Hypervalent Silicon IntermediatesFirst hypervalent allylsilane intermediatesOHTBAFOY3Si Ph1-41234Me3SiF3Si )6(%)ratio of5:6232301715 19158 : 4261 : 390 : 100Ph6Allylic transpositionAllylic trimethylsilane gave two regioisomers.However, allylic trifluorosilane gave only a singleisomer with allylic transposition. Thus, the reaction ofthe allylic trifluorosilane is quite regiospecific.F F-Me3SiFF4SiPhCHOHPhPentavalent siliconStabilized by fluorinesStrong Lewis acidSiF4O6-membered cyclic TSHexavalent siliconHigh nucleophilicityOHPhsingle isomerSakurai, H. Synlett 1989, 1.
Hypervalent Silicion in Organic ChemistryLewis Base Mediated Diastereoselective AllylationLewis Base Mediated Addition of Crotylsilanes to AldehydesSiF3 R(E)-CrotylsilaneH(Z)-Crotylsilane RTHF, r.t.HTHF, r.t.68-96% yieldanti/syn 98/2ROHCsFOSiF3OHCsFO77-96% yieldanti/syn 2/98RR aryl, alkylKira, M.; Kobayashi, M.; Sakurai, H. Tetrahedron Lett. 1987, 28, 4081.Kira, M.; Hino, T.; Sakurai, H. Tetrahedron Lett. 1989, 30, 1099.Lewis acid catalyzed addition of crotylsilanes to aldehyde generally gives syn-products via linear transition stateregardless of starting E/Z isomers. In contrast, Lewis base mediated addition of (E)-Crotylsilanes gave anti-products via 6membered cyclic transition state. Of course, (Z)-Crotylsilanes gave tylsilaneOHHORF-anti-productOHHSiF4RORThis result strongly suggests that this reaction occurs via 6-membered transition state.Rsyn-product
Hypervalent Silicion in Organic ChemistryLewis Base Catalyzed Allylation via Hypervalent Silicon IntermediatesReactivity and Chemoselectivity of AllysilanesSiF4O FSiOFO OSiO OF3CF3COSiOLewis acidityhighlowsteric hindarancesmalllargereactivityhighlowno reactionselectivitylowhighno reactiondiscriminate linearfrom !-branchedalkanalsCF3CF3only react with aromaticaldehydes under reflux in THFKira, M.; Sato, K.; Sakurai, H. J. Am. Chem. Soc. 1988, 110, 4599.Kira, M.; Sato, K.; Sakurai, H. J. Am. Chem. Soc. 1990, 112, 257.Does "-position of hypervalent allylic silanes really possess high reactivity?XXSi XXX XSi XX-low13C-NMRXNu# - conjugation effectX XSi XNuhighchemical shift of the "-carbon showed a higher field shift as silicon's electron-donating ability incresed.Grishin, Y. K.; Sergeyev, N. M.; Ustynyuk, Y. A. Org. Magn. Reson. 1972, 4, 377.
Hypervalent Silicion in Organic ChemistryNeutral Lewis Base Mediated AllylsilylationDramatic Solvent Effect on Allylsilyation of AldehydesOHOSiCl3 solventPhtemp. ( C)CH2Cl2CH3CNbenzeneEt2OTHFDMFHMPACH2Cl2-HMPA (2:1)r.t.r.t.r.t.r.t.r.t.000solventHPhtime (h)yield e allylation of aldehydes using allyltrichlorosilanesproceeded smoothly in DMF or HMPA as a solventwithout any additives!Does this allylation reaction in DMF proceeds via theneutral hypervalent silicon intermediate as shownbelow?Me2NMe2NOHHSiCl3DMF coordinated to silicon atom?HORCHOSiCl3OHRORKobayashi, S.; Nishio, K. Tetrahedron Lett. 1993, 34, 3453.Kobayashi, S.; Nishio, K. J. Org. Chem. 1994, 59, 6620.
Hypervalent Silicion in Organic ChemistryNeutral Lewis Base Catalyzed AllylsilylationDiastereoselective Allylation of Aldehydes using Crotyltrichlorosilanes in DMFOHOSiCl3 PhHDMF, 0 C89% yieldanti/syn 97/3PhE/Z 97/3OHOSiCl3 PhHDMF, 0 C82% yieldanti/syn 1/99PhE/Z 1/99These high diastereoselectivities can be explained by 6-membered cyclic transition state.29Si-NMRChemical Shifts of (Z)-Crotyltrichlorosilane in Several cal shift (ppm) 8.0 8.6 7.9 8.5-170-22This 29Si-NMR spectra of (Z)-crotyltrichlorosilane indicated that DMF orHMPA coordinated to the silicon atom of (Z)-crotyltrichlorosilane toform the corresponding penta- or hexavalent silicate.Me2NOSiCl3HMe2N NMe2P NMe2OSiCl3Kobayashi, S.; Nishio, K. Tetrahedron Lett. 1993, 34, 3453.Kobayashi, S.; Nishio, K. J. Org. Chem. 1994, 59, 6620.
Hypervalent Silicion in Organic ChemistryChiral Lewis Base Mediated Asymmetric Allylation of AldehydesAllylation of Benzaldehyde using Allyltrichlorosilane and 1 equiv of AdditivesSiCl3additiveDMFHMPAHMPAHMPA solventC6D6C6D6CDCl3CD3CNPhOHadditive (1 eq.)OHsolvent, r.t.conversion(%)t1/2 (min)18-83 (70 h)63 (4 min)63 (4 min)Phisolatedyield (%)778586Kobayashi has shown that DMF is an efficient promoter as solvent. However, Denmark found that 1 equiv of DMF in benzeneis relatively less effective than that of HMPA, which promoted complete conversion within minutes.Chiral Phosphoramide Mediated Asymmetric Allylation of Aromatic Aldehydes using AllyltrichlorosilanesSiCl3 ArOHcatalyst (1 eq.)OHCH2Cl2-78 C, 6 hAr67-81% yield21-65% eeOnly aromatic aldehyde underwent allylation in good yields, but electron-donatingand electron-withdrawing substituents dramatically reduced enantioselectivity.MeN OPN NMecatalystDenmark, S. E.; Coe, D. A.; Pratt, N. E.; Griedel, B. D. J. Org. Chem. 1994, 59, 6161.
Hypervalent Silicion in Organic ChemistryChiral Lewis Base Catalyzed Asymmetric Allylation of AldehydesDenmark also tried catalytic amount of chiral phosphoramideSiCl3 Phcatalyst(equiv)time (h)yield (%)1.00.50.250.1624242481787440PNPhCH2Cl2-78 C, timeHNcatalystee (%)60575953ONOHcatalystOWith as little as 25 mol% of catalyst, the yield is only sightly reducedand the enantioselectivity essentially the same.Denmark, S. E.; Coe, D. A.; Pratt, N. E.; Griedel, B. D. J. Org. Chem. 1994, 59, 6161.Chiral Formamide Catalyzed Asymmetric Allylation of Aliphatic AldehydeR1SiCl3R1 Me, H ROHcatalyst 20-40 mol%HMPA 100-200 mol%OHaliphatic aldehydesEtCN, -78 CRR151-94% yield68-98% eePhNPhHOcatalyst(DMF analogue)HMPA can promote a diisociation of the chiral formamide from silicon atom in the product by ligand exchange toregenerate the chiral formamide. Only aliphatic aldehydes gave good to high enantioselectivity. Aromatic aldehyde alsogave good yield but low enantioselectivity was observed.Iseki, K.; Mizuno, S.; Kuroki, Y.; Kobayashi, Y. Tetrahedron Lett. 1998, 39, 2767.Iseki, K.; Mizuno, S.; Kuroki, Y.; Kobayashi, Y. Tetrahedron Lett. 1999, 55, 977.
Hypervalent Silicion in Organic ChemistryChiral Bidentate Lewis Base Catalyzed Asymmetric Allylation of AldehydesChiral N-Dioxide Catalyzed Asymmetric Allylation of Aromatic AldehydeSiCl3catalyst (10 mol%)i-Pr2EtN (5 equiv)O ArHOHCH2Cl2-78 C, 6 hNPh68-91% yield71-91% eeNO OcatalystBidentate Lewis base enhanced the enantioselectiviy. This is probably because the allylation mediated by the bidentate Ndioxide catalyst proceeds via rigid 6-membered cyclic chairlike transition state as shown below, where one of a pair of Noxide moieties occupies an axial position. DIPEA can promote a diisociation of the chiral catalyst from silicon atom in theproduct.ClClOArHSiCl OONNaxial positionmaking this structure regid?Nakajima, M.; Saito, M.; Shiro, M.; Hashimoto, S. J. Am. Chem. Soc. 1998, 120, 6419.
Hypervalent Silicon in Organic ChemistryContents Structure and Property of Hypervalent SiliconHydrosililation as a Hypervalent Silicon ExampleLewis Base Catalyzed AllylsilylationDenmark’s Contribution to Lewis Base CatalyzedAldol Reaction and Allylsilylation Other Examples of Hypervalent SiliconNucleophilicity Hypervalent Silicon as a Chiral Lewis Acid
Hypervalent Silicion in Organic ChemistryLewis Base Catalyzed Aldol Reaction via Hypervalent Silicon IntermediatesDenmark thought if Lewis base catalyzed allylation strategies could apply to aldol reaction.OSiCl3O , -80 CHadditiveOHadditivetime (h)nonenonenoneHMPA 0.1 eq.120120120 3conversion (%)185069100Ot-BuOCH3Surprisingly, trichlorosilyl ketene acetal reactedspontaneously with a number of aldehydes at -80 C.Only pivalaldehyde reacted slowly enough to be followedspectroscopically.On pivalaldehyde, the accelation was observed with acatalytic amount of HMPA.Denmark also tried chiral phosphoramide.OSiCl3OCH3O ROHcatalyst (10 mol%)HR Ph, t-BuCH2Cl2, -78 CRPhOONPOCH3R Ph : 38% eeR t-Bu : 40% eePhNNcatalystPoor enantioselectivity was observed probably because of the intervention of the uncatalyzed pathway.Denmark, S. E.; Winter, S. B. D.; Su, X.; Wong, K.-T. J. Am. Chem. Soc. 1996, 118, 7404.
Hypervalent Silicion in Organic ChemistryLewis Base Catalyzed Asymmetric Aldol ReactionChiral Phosphoramide Catalyzed Asymmetric Aldol Reaction of Trichlorosilyl Ketone EnolatesOSiCl3OOcatalyst (10 mol%) RPhOHHCH2Cl2, -78 C, 2 h94-98% yieldsyn/anti 1/6188-97% ee (anti)RR aryl, cinnamylThe corresponding uncatalyzed reaction at 0 C gave high syn selectivity (syn/anti 5.7/1).ONPPhNNcatalystTrichlorosilyl ketone enolates were also highly reactive but much less reactive than trichlorosilyl ketene enolates. Thus, chiralphosphoramide catalyzed aldol reaction proceeded with high selectivity. Surprisingly, uncatalyzed aldol reaction of Eenolate gave syn adduct while Lewis base catalyzed reaction gave anti adduct .This is because pentavalent siliconate transition structures were shown computationally to prefer boat-like arrangementswhile hexavalent siliconate to prefer chair-like lRPentavalent silicon intermediateBoat-like transtion stateHexavalent silicon intermediateChair-like transtion stateDenmark, S. E.; Wong, K.-T.; Stavenger, R. A. J. Am. Chem. Soc. 1997, 119, 2333.Denmark, S. E.; Stavenger, R. A.; Wong, K.-T. J. Org. Chem. 1998, 63, 918.
Hypervalent Silicion in Organic ChemistryMechanistic Duality in the Lewis Base Catalyzed Aldol ReactionDramatic Switch in Diastereoselectivity with Phosphoramide StructuresOSiCl3OO PhPhPhHMeN OPN NOHOcatalyst 10 mol%PhPhMe Phanti adductPhN OPN Ncatalystcatalyst (2)syn adductyield (%)(1)(2)Phcatalyst (1)PhCH2Cl2, -78 COHanti/syn959460/11/97ee92 (anti)51 (syn)Lewis base catalyzed aldol reaction proceeds via differenttransition states due to phosphoramide structures?Denmark's Observation on the Influence of the Catalyst Concentration on SelectivityOSiCl3OOOHcatalyst (1)catalyst (1) PhPhHCH2Cl2, -75 C10 mol%2 mol%0.5 mol%anti/syn 50/128/15/1anti adductThe syn/anti selectivity dramatically decreased with decreased loading of catalyst (1).Lewis base catalyzed aldol reaction proceeds via different competitive transition states due to catalyst concentration?Denmark, S. E.; Su, X.; Nishigaichi, Y. J. Am. Chem. Soc. 1998, 120, 12990.Denmark, S. E.; Stavenger, R. A. Acc. Chem. Res. 2000, 33, 432.
Hypervalent Silicion in Organic ChemistryMechanistic Duality in the Lewis Base Catalyzed Aldol ReactionDenmark's Observation on Non-linear Effect of Chiral Phosphoramide Catalyzed Aldol ReactionOOSiCl3OOcatalyst 10 mol% PhOHHPhCH2Cl2, -78 CPhPhMeN OPN NMecatalyst (1)PhPhPhN OPN NPhcatalyst (2) Phsyn adduct% ee of productanti adductOHA positive non-linear effect was only measured using catalyst (1)and no asymmetric amplification was seen using catalyst (2).Those results strongly suggest that relatively less bulkylphosphoramide catalyzed aldol reaction proceeds via a transition stateincluding more than one phosphoramide molecule.% ee of catalyst (1)or (2)Denmark, S. E.; Su, X.; Nishigaichi, Y. J. Am. Chem. Soc. 1998, 120, 12990.Denmark, S. E.; Stavenger, R. A. Acc. Chem. Res. 2000, 33, 432.
Hypervalent Silicion in Organic ChemistryMechanistic Duality in the Lewis Base Catalyzed Aldol ReactionProposed Pathway to the Two DiastereomersNR2OSiCl3OH PhHPhPhMeN OPN NMerelatively less bulkyOHPhPhrelatively more bulkyPhN OPN NPhOHPhanti adduct92% eenon-linear effectClOSiO PhClPhHexavalent silicon intermediateCationic chair-like transition statePhOOClSiOHOSiCl3NR2P NR2NR2OR2N PR2NOOClNR2P NR2NR2OOHPhsyn adduct50% eePentavalent silicon intermediateCationic boat-like transition stateno asymmetric amplificationThis mechanism explains the different diastereoselectivity by phosphoramide structures and concentrasion, non-linear effect byrelatively less bulky phosphoramide, and low enantioselectivity of syn adduct.Denmark, S. E.; Su, X.; Nishigaichi, Y. J. Am. Chem. Soc. 1998, 120, 12990.Denmark, S. E.; Stavenger, R. A. Acc. Chem. Res. 2000, 33, 432.
Hypervalent Silicion in Organic ChemistryMechanistic Duality in the Lewis Base Catalyzed AllylsilylationDenmark thought the same mechanistic duality in allysilylation as aldol reaction.SiCl3catalyst (1 equiv)O PhHOH-78 C, 6 hPhpositive non-linear effectPhMe% ee of productDenmark also determined the overall rate expression.According to that, the reaction is overall second order,and first order in allylsilane and benzaldehyde.A In/In plot of the second-order rate constants(ln(k)) versus the catalyst concentration(In[catalyst]) gave a straight line with a slope of 1.77.This result also suggests the presence of more thanone molecules of catalyst in the stereochemicallydetermining transition structure.PhcatalystA positive non-linear effect was measured on allylationreaction, too. This result suggests the presence of twomolecules of catalyst in the stereochemicallydetermining transition structure.The rate expressionv k[allylsilane][benzaldehyde]A plot of k versus [catalyst]2 give a straight line.60% eeMeN OPN N% ee of catalystDenmark, S. E.; Fu, J. J. Am. Chem. Soc. 2000, 122, 12021.
Hypervalent Silicion in Organic ChemistryMechanistic Duality in the Lewis Base Catalyzed AllylsilylationProposed Two Transition Structures in the Lewis Base Catalyzed AllylsilylationNR2ClHPhOSiOClNR2HP NR2NR2NR2P NR2NR2OR2N PR2NOPhOSiClClPentavalent silicon intermediateCationic boat-like transition stateHexavalent silicon intermediateCationic chair-like transition statehigh selective pathwayless selective pathwayA competing less selective pathway would reduce the enantioselectivity of this phosphoramide catalyzed reaction?Thus, Denmark tried a bidentate chiral phosphoramide catalyst.R1SiCl3R2R1 H, MeR2 H, Me i-Pr2EtN, CH2Cl2-78 C, 8-10 hR aryl, cinnamyl, furylROHcatalyst (5 mol%)OHRR1 R267-92% yield80-96% ee99/1 drHHONOPNNPNMe5NNHHMecatalystDenmark's well thought-out bidentate chiral phosphoramide strategy sccessfully gave high enantioselectivity!Denmark, S. E.; Fu, J. J. Am. Chem. Soc. 2001, 123, 9488.
Hypervalent Silicion in Organic ChemistrySynthetically Useful Application of Denmark's Bisphosphoramide CatalystAsymmetric Construction of Quaternary CentersMeSiCl3catalyst1 (10 mol%)Bu4N I-O PhPhCH2Cl2, -78 CHNONROHOCH3PhHPh Me92% yield99/1 dr, 94% eeHONOPNNPN5NMeNHHMecatalyst1R phenylR cyclohexylPh MeSerotonin Antagonist LY426965The first application of catalytic, enantioselective allylation to generate quaternary carbon centers!!Denmark, S. E.; Fu, J. Org. Lett. 2002, 4, 1951.Asymmetric Crossed Aldol Reaction of AldehydesOSiCl3n-C5H11 PhHCHCl3/CH2Cl2 4:1-78 C, 6 h;then MeOHCl3SiOOThe First AsymmetricCrossed Aldol Reactonof Aldehydes!!OHcatalyst2 (5 mol%)OPhPhOMen-C5H1192% yield99/1 dr, 90% eeCl2SiOOHn-C5H11PhOMeMeONPNNMe MeCl2catalyst2n-C5H11Denmark, S. E.; Gosh, S. K. Angew. Chem. Int. Ed. 2001, 40, 4759.
Hypervalent Silicon in Organic ChemistryContents Structure and Property of Hypervalent SiliconHydrosililation as a Hypervalent Silicon ExampleLewis Base Catalyzed AllylsilylationDenmark’s Contribution to Lewis Base CatalyzedAldol Reaction and Allylsilylation Other Examples of Hypervalent SiliconNucleophilicity Hypervalent Silicon as a Chiral Lewis Acid
Hypervalent Silicion in Organic ChemistryLewis Base Catalyzed Propargylation and Allenylation of AldehydesThe Addition of Allenyl- and Propargyltrichlorosilanes to AldehydesHSiCl3CuCl, i-Pr2EtNEt2OOHSiCl3SiCl3 RCHORDMFHSiCl3Ni(acac)2, i-Pr2EtNEt2OSiCl3 99 : 155-92% yieldR Aryl, AlkylSiCl3 OHRCHORDMFR 1 : 9956-90% yieldProposed transition statesHH SiClxDFMyOOH 1 : 99RR Cl 99 : 1OHSiClxDFMyROKobayashi, S.; Nishio, K. J. Am. Chem. Soc. 1995, 117, 6392.Schneider, U.; Sugiura, M.; Kobayashi, S. Tetrahedron 2006, 62, 496.
Hypervalent Silicion in Organic ChemistryLewis Base Catalyzed Asymmetric Propargylation of AldehydesAsymmetric Propargyltrichlorosilanes to Aldehydes with AllenyltrichlorosilaneSiCl3 catalyst (10 mol%)i-Pr2EtNO ArHProposed Stereochemical ModelsCH2Cl2OHPyNOAr55-98% yield74-96% eecatalystThe Si face addition is favored due to theexpected !-stacking between the boundaldehyde and the helicene framework.In contrast, the 11, 12- benzo unit is veryclose to the aldehyde bound in the Reface addition mode.Chen, J.; Captain, B.; Takenaka, N.Org. Lett. 2011, 13, 1654.
Hypervalent Silicion in Organic ChemistryLewis Base Catalyzed Other C-C Bond-Forming Reactions via Hypervalent SiliconChiral Amino Acid Salt Catalyzed Asymmetric Cyanosilylation to KetonesO Phcatalyst (30 mol%)TMSCNIPA, THF, -45 CMePhMe Si MeMeCatPentavalent siliconStrong Lewis acidCOONaMe96% yield94% eeCatMeMeSiMeOCNCNNH2TMSO CNMePhHexavalent silliconHigh nucleophilicitycatalystLiu, X.; Oin, B.; Zhou, X.; He, B.; Feng, X.J. Am. Chem. Soc. 2005, 127, 12224.Lewis Base Catalyzed Alkynylsilylation to KetonesOEtOEtO SiEtOR1 R1R2KOEt (10 mol%)R3OEtSi OEtOEtLBPentavalent siliconStrong Lewis acidTHF, 0 CR3OHR1, R2, R3 Aryl, AlkylR254-93% yieldR1R1R2OEtOEtSiOOEtLBR3Hexavalent silliconHigh nucleophilicityLettan, R. B., II; Scheidt, K. A. Org. Lett. 2005, 7, 3227.
Hypervalent Silicon in Organic ChemistryContents Structure and Property of Hypervalent SiliconHydrosililation as a Hypervalent Silicon ExampleLewis Base Catalyzed AllylsilylationDenmark’s Contribution to Lewis Base CatalyzedAldol Reaction and Allylsilylation Other Examples of Hypervalent SiliconNucleophilicity Hypervalent Silicon as a Chiral Lewis Acid
Hypervalent Silicion in Organic ChemistryHypervalent Silicon as a Chiral Lewis AcidAsymmetric Propargylation of AldehydesSnBu3O PhH MeSiCl4 (1.1 equiv)catalyst (5 mol%)CH2Cl2, -78 C, 8 hONOHPNPhNMe Me81% yield97% eeAllyltributyltin also gave the homoallylic alcohol with high yield and enantioselectivity.2catalystDenmark, S. E.; Wynn, T. J. Am. Chem. Soc. 2001, 123, 6199.Asymmetric Addition of Silyl Ketene Acetals to AldehydesOTBSOPh HOt-BuMeSiCl4 (1.1 equiv)catalyst (1 mol%)OHPhCH2Cl2, -78 C, 3 hOOt-BuAddition of silyl ketene acetalsproceeded via acyclic transitionstate to give anti products.MeE/Z 95/5 : 93% yield, 99% ee, 99/1 drE/Z 12/88 : 73% yield, 99% ee, 99/1 drDenmark, S. E.; Wynn, T.; Beutner, G. L. J. Am. Chem. Soc. 2002, 124, 13405.Denmark, S. E.; Beutner, G. L.; Wynn, T.; Eastgate, M. D. J. Am. Chem. Soc. 2005, 127, 3774.SiCl4(R2N)3P O(R2N)3POO(R2N)3PSiClClClClin situ generatedchiral Lewis acid
Hypervalent Silicion in Organic ChemistryHypervalent Silicon as a Chiral Lewis AcidAsymmetric Addition of Silyl Enol Ethers of AldehydesSiCl4 (1.5 equiv)OTMSOcatalyst (5 mol%) i-Pr2EtN (10 mol%)n-BuPhHCH2Cl2, -72 C, 3 hMeOHOONPhPn-BuN99% yield99% eeNMe Me2catalystDenmark, S. E.; Heemstra, Jr., J. R.; Org. Lett. 2003, 5, 2303.Asymmetric Vinylogous Aldol ReactionOTBSOPh HMe!"Ot-BuSiCl4 (1.1 equiv)catalyst (1 mol%)OHOPhOt-Bu92% yield, !/" 99/1 99/1 dr, 89% eeDenmark, S. E.; Beutner, G. L. J. Am. Chem. Soc. 2003, 125, 7800.Denmark, S. E.; Heemstra, Jr., J. R. J. Am. Chem. Soc. 2006, 128, 1038.CH2Cl2, -78 C, 3 hEnantioselective Passerini-Type ReactionOPh Ht-BuNCSiCl4 (1.5 equiv)catalyst (5 mol%)i-Pr2EtN (10 mol%)CH2Cl2, -74 C, 4.5 h;then sat. aq. NaHCO3OHPhNHt-BuThe first catalytic asymmetric "addition of isocyanides.O93% yield93% eeDenmark, S. E.; Fan, Y. J. Am. Chem. Soc. 2003, 125, 7825.Denmark, S. E.; Fan, Y. J. Org. Chem. 2005, 70, 9667.
Hypervalent Silicion in Organic ChemistryHypervalent Silicon as a Chiral Lewis AcidEnantioselective Ring Opening of EpoxidesSiCl4 (1.2 equiv)catalyst1 (5 mol%)OPhPhOCH2Cl2, -85 C, 24 hPhCl-LBPhHONArClFeAr88% yield94% eeAr 3, 5-(CH3)2C6H3Arcatalyst1ArArLBClSiClClOPhPhTao, B.; Lo, M. M.-C.; Fu, G. C. J. Am. Chem. Soc. 2001, 123, 353.Strained Silacycle-Catalyzed Asymmetric Diels-Alder Cycloaddition MeCHOcatalyst2 (20 mol%)CH2Cl2, -78 C, 8 hCHOMe78% yield94% eeStrain release Lewis acidity!!Ring strain exsists including silicon.TsNClSiNcatalyst2Kubota, K.; Hamblett, C. L.; Wang, X.; Leighton, J. L. Tetrahedron 2006, 62, 11397.
Hypervalent Silicon in Organic ChemistrySummary Hypervalent silicon is crucial intermediate in Lewisbase catalyzed allylsilylation and aldol reaction.Using chiral Lewis bases, these reactions could givehigh diastereo- and enantioselectivity. Hypervalent silicon is also used as chiral Lewis acidcatalyst in aldol reaction, ring opening of epoxides,Diels-Alder cycloaddition and so on.
First Lewis Base Catalyzed Hydrosilylation 80% Boyer, J.; Corriu, R. J. P.; Perz, C. Tetrahedron, 1981, 37, 2165. H EtO OEt OEt CsF Pentavalent silicon Stabilized by electronegative atoms Strong Lewis acid PhMe O F Si H EtOOEt Tetravalent silicon Rather strong Lewis acid due to electronegative atoms Weak Lewis acid SiOEt H F Cs Si EtO EtOOEt O .
Chemistry ORU CH 210 Organic Chemistry I CHE 211 1,3 Chemistry OSU-OKC CH 210 Organic Chemistry I CHEM 2055 1,3,5 Chemistry OU CH 210 Organic Chemistry I CHEM 3064 1 Chemistry RCC CH 210 Organic Chemistry I CHEM 2115 1,3,5 Chemistry RSC CH 210 Organic Chemistry I CHEM 2103 1,3 Chemistry RSC CH 210 Organic Chemistry I CHEM 2112 1,3
Lewis Base Catalysis Introduction Base catalyzed acylation of alcohols Rendler, S.; Oestreich, M. "Hypervalent Silicon as a Reactive in Site Selective Bond-Forming Processes" Synthesis 2005, 11, 1727 Storer, I. MacMillan Group Seminar " Hypervalent Silicon" July 2005 Denmark, S. E.; Beutner, G. L., "Lewis Base Catalysis in Organic Synthesis."
Textbook Essentials of Organic Chemistry by Dewick The following textbooks are also available in the chemistry library on reserve: Organic Chemistry: A Short Course by Hart, Craine, Hart and Hadid Introduction to Organic Chemistry by Brown and Poon Fundamentals of Organic Chemistry by McMurry Essential Organic Chemistry by Bru
In Press Advanced Inorganic Chemistry Gurdeep Raj 06 270 Chromatography B.K. Sharma 06 Organic Chemistry 302 Advanced Organic Chemistry Aditi Singhal 08 279 Organic Chemistry Natural Products - Vol. I O. P. Agarwal 09 280 Organic Chemistry Natural Products - Vol. II O. P. Agarwal 09 281 Organic Chemistry Reactions & Reagents O. P. Agarwal 10
The CMOS Process - photolithography (1) Silicon Wafer Silicon Wafer SiO 2 1μm Silicon Wafer photoresist (a) Bare silicon wafer (b) Grow Oxide layer (c) Spin on photoresist Lecture 3 - 4 The CMOS Process - photolithography (2) Silicon Wafer (d) Expose resist to UV light through a MASK Silicon Wafer (e) Remove unexposed resist Silicon Wafer
CHEM 0350 Organic Chemistry 1 CHEM 0360 Organic Chemistry 1 CHEM 0500 Inorganic Chemistry 1 CHEM 1140 Physical Chemistry: Quantum Chemistry 1 1 . Chemistry at Brown equivalent or greater in scope and scale to work the studen
Physical chemistry: Equilibria Physical chemistry: Reaction kinetics Inorganic chemistry: The Periodic Table: chemical periodicity Inorganic chemistry: Group 2 Inorganic chemistry: Group 17 Inorganic chemistry: An introduction to the chemistry of transition elements Inorganic chemistry: Nitrogen and sulfur Organic chemistry: Introductory topics
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