Organosilicon Chemistry

Question 1

Silicon protecting groups used for

Answer 1

Alcohols as Si-O bond is strong

Question 2

Deprotection of silicon

Answer 2

Fluoride as Si-F is strong

Question 3

Stability of silyl protecting groups

Answer 3

more steric bulk gives a more stable Si protecting group

Question 4

Addition of Si protecting groups

Answer 4

use corresponding silyl chloride, proceeds via Sn2 reaction

Question 5

Silicon b-effect

Answer 5

Si stabilises b-carbocations due to hyperconjugation, C-Si bond overlaps and stabilises empty p-orbital but needs correct alignment

Question 6

Electrophilic attack of aryl silanes

Answer 6

undergo ipso attack due to b-C stabilisation

Question 7

Peterson olefination

Answer 7

uses Me3Si-CH2-MgCl, similar to wittig but more reactive
in base undergoes syn elimination giving cis-alkene
in acid undergoes anti elimination giving trans-alkenes

Question 8

Use of silyl enol ethers

Answer 8

stable enolate equivalents

Question 9

Formation of silyl enol ethers

Answer 9

Aldehyde/ketone and LDA at -78C then Me3SiCl gives kinetic enolate
Aldehyde/ketone and Et3N and Me3SiCl at high T gives thermodynamic enolate