Question

1. Draw the product structure and propose a reasonable mechanism for the following reactions: NBS, H,0 DMSO C,H,OBT 1. BH, THE 2. H2O2, OH

Answer 1

1.

a)

First step bromonium ion is formed.

Second step involves nucleophilic attack by water molecule from backside to give two enantiomers .

Attack from less hindered side (b) gives the major product

Bn

Вя5 a В1 Вл он2 о он СО ВИ ВЯ н + он

b.

BH₃ undergoes addition reaction to double bond , the boron atom gets attached to the less substituted doubly bonded carbon predominantly .

Hydrogen peroxide in presence of OH^- give hydroperoxide ion which attacks the electron deficient boron atom and forms an intermediate. Further after rearrangement trialkyl borate ester is formed. The borate ester after hydrolysis results the final primary alcohol product.

BH3 H- Syn adolition 2 BH2 H-0-0-H tOH E R 1L H20t Hoo OOH o o- H R3 B R +OH R 2 B-0-R OH R2-B

H202/0H R28-0 OR 3 -OR)2 R - L H202/애- O B OR)3 O H OR2 R-O HO BLOR)2 RoO H20 oH ROH + 아H