Electrophilic Substitution of Hydrogen in Betulin and Diacetylbetulin

Betulin and diacetylbetulin, which can be regarded as sterically hindered alkenes, reacted with N-chloro-, N-bromo-, and N-iodosuccinimides to give products of allylic and vinylic substitution in quantitative overall yield. The contribution of allylic substitution increases in the series Cl < Br < I. Quantum chemical simulation of the reactions of diacetylbetulin with N-halosuccinimides showed that, regardless of the electrophile power, all reactions involve open-chain carbocationic intermediates. The direction of deprotonation of the latter with formation of allylic or vinylic substitution products is determined by preferential orientation of the vacant orbital and C–Hlg bond.