Skeletal rearrangements and structures of halosulfonamidation products of caryophyllene

Abstract

The reactions of β-caryophyllene with sulfonamides in acetonitrile in the presence of N-bromo- and N-iodosuccinimide have been studied. With NBS, only 3-amidino-6-bromo-1,1,7-trimethyldecahydro-3a,7-methanocyclopenta[8]annulenes have been isolated. With NIS, some sulfonamides afford their isomeric iodine analogues, 1-amidino-9-iodo-4,4,8-trimethyltricyclo[6.3.1.0^2,5]dodecanes, also as single products, whereas the other reagents give mixtures of both types of products. The yields vary from good to excellent, and the structure of five products was proved by X-ray analysis. The proposed mechanism involves halogenation of the endocyclic CC bond, subsequent intramolecular cyclization and either solvent interception by the formed carbocation or, prior to interception, four- to five-membered ring expansion. The experimentally observed stereo- and regioselectivity of the reaction is explained.