— Physical Chemistry Chemistry Question

The solution shows the structures of the stereoisomers of compounds A to F:
- A: 3 stereoisomers (the shown structure, its enantiomer, and a diastereomer).
- B: 4 stereoisomers (the shown structure, its enantiomer, and two diastereomers).
- C: 4 stereoisomers (the shown structure, its enantiomer, and two diastereomers).
- D: No stereoisomers due to the facile racemization at the pyramidal N atom.
- E: 4 stereoisomers (the shown structure, two diastereomers, and its enantiomer).
- F: 2 stereoisomers (the shown structure and its enantiomer).
[VISUAL]

The primary step in the process is hydroboration of the olefin. This is a syn-addition and can give rise to two intermediates of which the one shown is favored for steric reasons. Reaction of the intermediate with hydrogen peroxide proceeds with the retention of chirality giving a major product with good diastereoselectivity. A little of the hydroboration might proceed from the other face of the molecule giving rise to a minor product after oxidative work up.

The so-called iodolactonization of olefins starts with the activation of the double bond by the electrophilic iodine giving the depicted intermediate. Since the top face of the double bond is sterically more hindered, attack is preferentially from the bottom. Intramolecular nucleophilic attack by the carboxylate ion on the iodonium species leads to diastereoselective formation of the depicted (sole) product.

Epoxidation of the double bond by meta-chloroperbenzoic acid is directed by steric factors. The predominant site of attack is the sterically less hindered side of the double bond giving the “threo” compound as the major product. Attack from the other face is less facile and only small amounts of the „erythro” product are formed.

Cis-dihydroxylation of the starting material by osmiumtetroxide gives rise to diastereoselective formation of the depicted product which exists as a mixture of enantiomers.

Catalytic hydrogenation proceeds on the surface of platinum and is a syn-addition of the hydrogen to the double bond. The preferred approach of the molecule to the catalyst surface is with the side bearing the smaller substituents. Since the steric demand of the phenyl and methyl groups exceeds that of the oxygen the reduction is diastereoselective and a single product is formed.

[VISUAL]