QUANTUM-CHEMICAL CHARACTERIZATION OF CYCLOADDITION REACTIONS BETWEEN THE HYDROXYALLYL CATION AND DIENES OF VARYING NUCLEOPHILICITY

Hydroxyallyl cation prefers to undergo cycloaddition reactions with di enes in a stepwise fashion. Analysis of positive charge distribution i n the intermediate formed after initial C-C bond formation provides a simple unifying method for rationalizing changes in reactivity as a fu nction of diene nucleophilicity. Predicted product distributions are c onsistent with results from experimental studies. Interestingly, for t he initial intermediate generated from 1,3-butadiene, [3 + 2] cycloadd ition reactions are favored, but closure to form a C-O bond as the sec ond step results in an intermediate that can undergo a. low-energy Cla isen rearrangement to form a seven-membered-ring product identical to that expected from compact [4 + 3] cycloaddition.