Complete the following reactions:
a.
b. Give the major products of the following:

Explanation

a. All the three reagents, namely, DIBAL-H, `LiAlH(O-t)Bu)_(3)` , and Lindlar's catalyst `(H_(2)+Pd+BaSO_(4))` reduce acid halides to aldehydes. The products (B), (C ) and (D) are same. Hydroxy aldehyhdes then undergo intramolecular reaction to give cylic hemicetal.

(A) on reaction with all three reagents gives (I), hydroxyaldehyde anion, which undergoes ring closure. During ring closure, a chiral centre is formed and as a reasult two enantiomeric forms are obtained and the product is a racemic mixture.
b. Bulky t-butyl group always occupies less hindered equatorial position in cylohexane.

i. The bulky `Sia_(2)BH` approaches `(C=O)` from the less hindered equatorial side, pushing (OH) to axial position which reasult in the formation of less stable cis-isomer.
ii. Less bulky LAH approaches `(C=O)` form the more hindered axial side, pushing (OH) to equatorial position, resulting in the more stable trans-isomer.
iii. With `H_(2)+Pt`, cis-alcohol is formed in major amount, because `H_(2)` is adsorbed on the surface of finely divided catalyst, and H approaches from the less hindered equatorial side and gives cis-alcohol as in (i).