Directional Specificity in the Boronate Cleavage of Unsaturated 1,3-Diol Derivatives

Abstract

Recently Miyashita, Yanami, and Yoshikoshi reported an apparent case of peripheral bond cleavage in the fragmentation of the boronate 2 derived from octalin 1 to give aldehyde 4 (Scheme I, Path a).¹ Since previous examples of related fragmentations had been shown to proceed with exclusive cleavage of the more highly substituted carbon-carbon bond² (i.e. 2 → 3) it was of interest to examine the above system in greater detail to determine if the neighboring hydroxyl substituent caused the unexpected bond cleavage or if an alternative pathway (Scheme I, Path b) might be operative in this case.³ To that end, we first examined the behavior of the methyl ether derivative (5) of alcohol 1 which was prepared along the lines described below for ether 15 (Scheme II). However hydroboration of unsaturated ether 5 followed by base treatment led to no identifiable product. Evidently steric factors retard the hydroboration and / or basic cleavage of the intermediate boronate.