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Organosilicon compounds
- 1. Prepared By Dr. Krishnaswamy. G Faculty DOS & R in Organic Chemistry Tumkur University Tumakuru Organo silicon Compounds
- 2. Monomeric silicons are known as Silanes. A silane that contain at least one carbon-silicon bond is known as Organosilanes. Si-C bond is covalent and silicon acts as electrophile. Introduction Silicon is just like carbon but It has larger size (atomic radius-117 pm) More electropositive (Si-1.64) Has greater affinity for electronegative atoms like F, Cl & O. C Si - + Nucleophile Electrophile
- 3. Direct synthesis by Rochow Muller process 2 RCl Si R2SiCl2 Cu 300o C Metathesis SiCl4 RLi R4Si Synthesis
- 4. H Si CC CC OC NC NC CC CC SiH OC NC NC H H Si H Si Si H Si Catalyst Hydrosilylation, also known as hydrosilation is one of the most useful catalytic reaction where addition of Si-H to unsaturated bond leads to the formation of organsilanes and organosilicones.
- 5. Reactions Protecting reactions Variation of three R group on silicon can provide an unlimited range of protecting group for O, N and C. R OH R O Si R R R R3SiCl Base R OH F Si R R R Protection Deprotection n-Bu4NF C H C Si R R R R3SiCl C BuLi C
- 6. H3C Si CH3 CH3H3C CH3 Si CH3H3C CH3 Si CH3H3C H3C H3C CH3 CH3 Tert-butyldimethylsilyl chloride TBDMS-Cl Triisopropylsilyl chloride TIPS-Cl Tert-butyldiphenylsilyl chloride TBDPS-Cl Cl Cl Cl H3C Si CH3 CH3H3C Cl Thexyldimethylsilyl chloride TDS-Cl H3C CH3 Common protecting groups
- 7. Ipso substitution Aryl silane undergo ipso electrophilic aromatic substitution reaction. Si R R R E Si R R R E E Nu para meta ortho ipso R3Si Stabilization of positive charge at β-position through hyperconjugation
- 8. Addition reaction Vinyl silane undergo addition reaction with electrophile with retention of configuration. H R SiR3 R E H R E R H R R SiR3 E H R R E Z-vinyl silane E-vinyl silane
- 9. Peterson olefination Preparation of alkenes from α-silyl carbanions and carbonyl compounds is known as Peterson olefination. R Si R R R1 R3R2 O R2 R1R3 H acid / base -silylcarbanions R Si R R R1 -silylcarbanions R Si R R R1 Cl R Si R R R1 MgCl Mg
- 10. R Si R R R1 R3R2 O -silylcarbanions R Si R R R1 OH R3 R2 R Si R R R1 OH R3 R2 H H -silylcarbinols Diastereomers Addition of α-silyl carbanions to carbonyl compounds give rise to mixture of diastereomeric silylcarbinols which can isolated and separated.
- 11. R Si R R R1 OH R3 R2 H -OH and -SiR3 syn Acid R Si R R R1 OH2 R2 R3 H R1 R2 R3H Z-alkene Pure diastereomers upon treatment with dilute acid (AcOH, H2SO4) or a lewis acid (BF3.OEt2) results in a stereospecific anti elimination to give alkene. R Si R R R1 OH R3 R2 H R Si R R R1 OH2 R3 R2 HAcid -OH and -SiR3 anti R1 R3 R2H E-alkeneanti-periplanar TS
- 12. R Si R R R1 OH R3 R2 H Base -OH and -SiR3 anti R Si R R R1 OH R3 R2 H -OH and -SiR3 syn Base R1 R3 R2H Z-alkene R Si R R R1 O R3 R2 H syn-periplanar TS R Si R R R1 O R3 R2 H Rotation of bond occurs to make SiR3 and Oxyanion syn Pure diastereomers upon treatment with base (NaH, KH, KOt-Bu) results in a stereo specific syn elimination to give alkene.
- 13. Me3Si OH -OH and -SiMe3 anti -OH and -SiR3 syn Z-alkene Me3Si OH2 Me3Si OH Acid Acid E-alkene Me3Si OH2
- 14. Me3Si OH Base -OH and -SiMe3 anti Me3Si OH -OH and -SiR3 syn Base Z-alkene Me3Si O syn-periplanar TS Me3Si O Rotation of bond occurs to make SiMe3 and Oxyanion syn
- 15. SUMMARY Anti elimination Syn elimination OH R3Si Anti E-alkene OH R3Si Syn Z-alkene Acid Acid OH R3Si Anti OH R3Si Syn Z-alkene Base