Oxymetallation. Part 18. Extensive rearrangement to a [4.2.1 ] skeleton in the bromodemercuriation of 2-bromomercurio-9-oxabicyclo[3.3.1]nonane

Abstract

The distributions of isomeric 2-bromo-9-oxabicyclononanes obtained by the brominolysis of trans-2-brompmercurio-9-oxabicyclo[4.2.1]nonane and of trans-2-bromomercurio-9-oxabicyclo[3.3.1]nonane in methanol with added sodium bromide, in dichloromethane and in pyridine, and from the bromination of 5-trimethylsilyloxycyclo-octene and of 5-t-butyloxycyclo-octene have been determined using ¹³C n.m.r. spectroscopy. Whereas the product distributions are generally in keeping with established mechanisms, the bromodemercuriation of the [3.3.1]mercurial in methanol with added sodium bromide affords the trans-[4.2.1]bromide as the major product. It is suggested that this novel skeletal rearrangement occurs via a sequence of deoxymercuriation and bromination.