Organosilicon compounds

This presentation has important synthesis and reactions of organosilanes like protection reaction, ipso substitution, Peterson olefination.

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.

3. Direct synthesis by Rochow Muller process Metathesis Synthesis

4. 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.

6. Common protecting groups

7. Ipso substitution Aryl silane undergo ipso electrophilic aromatic substitution reaction. Stabilization of positive charge at β - position through hyperconjugation

8. Addition reaction Vinyl silane undergo addition reaction with electrophile with retention of configuration.

9. Peterson olefination Preparation of alkenes from α - silyl carbanions and carbonyl compounds is known as Peterson olefination .

10. Addition of α - silyl carbanions to carbonyl compounds give rise to mixture of diastereomeric silylcarbinols which can isolated and separated.

11. Pure diastereomers upon treatment with dilute acid ( AcOH , H 2 SO 4 ) or a lewis acid (BF 3 .OEt 2 ) results in a stereospecific anti elimination to give alkene.

12. Pure diastereomers upon treatment with base ( NaH , KH, KOt -Bu) results in a stereo specific syn elimination to give alkene.

13. SUMMARY Anti elimination Syn elimination