Elemental F₂ with Transannular Dienes: Regioselectivities and Mechanisms

Abstract

Three reaction paths, namely, molecule-induced homolytic, free radical, and electrophilic, were modeled computationally at the MP2 level of ab initio theory and studied experimentally for the reaction of F2 with the terminal dienes of bicyclo[3.3.1]nonane series. The addition of fluorine is accompanied by transannular cyclization to the adamantane derivatives in which strong evidence for the electrophilic mechanism both in nucleophilic (acetonitrile) and non-nucleophilic (CFCl3 , CHCl3 ) solvents were found. The presence of KF in CFCl3 and CHCl3 facilitates the addition and substantially reduces the formation of tar products.

Synthesis of 1,2-Disubstituted Adamantane Derivatives by Construction of the Adamantane Framework

“…The addition of elemental fluorine (F 2 ) to unsaturated systems can either proceed as a radical process or has an electrophilic ionic nature (Scheme 13). Both pathways would leave a 'footprint' in product distributions starting from 45ab, where a radical process would favor noradamantyl derivatives, in contrast to the electrophilic ionic pathway preferring the transannular cyclization towards adamantyl cations, as predicted by computational studies [62].…”

“…Reactions in wet acetonitrile successfully trapped the cationic intermediates, forming the corresponding acetamides 52ab and 53ab. Additional fluorination also resulted in the formation of side products 54ab and 55ab [62].…”