SYNTHETIC UTILITY AND MECHANISTIC STUDIES OF THE ALIPHATIC REVERSE BROOK REARRANGEMENT

The aliphatic reverse Brook rearrangement has been examined in detail. Transmetalation of [α-[(trialkylsilyl)-oxy] alkyl]trialkylstannanes occurs via a complex equilibrium favoring the most stable carbanion. The aliphatic reverse Brook rearrangement is driven forward by the rapid migration of silicon from O to C in a transient α-silyloxy carbanion due to the formation of the more stable lithium alkoxide. Cross-over experiments have shown that the rearrangement is an intramolecular process while incorporation of a radical trap revealed that the rearrangement does not involve radical intermediates. Studies of configurationally fixed stannanes derived from 4-tert-butylcyclohexanone concluded that the rearrangement occurs with retention of configuration. Preparation and reverse Brook rearrangement of optically active (S)-[α-[(trimethylsilyl)oxy]-hexyl]tributylstannane (98% ee) provided 1-(trimethylsilyl)hexanol in 97% ee. The synthetic utility of this method for the preparation of a variety of (α-hydroxyalkyl)trialkylsilanes from aldehydes has also been demonstrated. © 1990, American Chemical Society. All rights reserved.