Cj. Cramer et Se. Barrows, QUANTUM-CHEMICAL CHARACTERIZATION OF CYCLOADDITION REACTIONS BETWEEN THE HYDROXYALLYL CATION AND DIENES OF VARYING NUCLEOPHILICITY, Journal of organic chemistry, 63(16), 1998, pp. 5523-5532
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.