Regioselectivity in the Diels-Alder reaction of 8,8-dimethylnaphthalene-1,4,5(8H)-trione with 2,4-hexadien-1-ol

The Diels-Alder reactions of 8,8-dimethylnaphtalene-1,4,5(8H)-trione with 2 ,4-hexadien-1-ol and its O-acetyl derivative were investigated in different solvents. The regiochemistry of the cycloaddition of the hexadienol was de termined through chemical correlation of one of the products. The solvent e ffect on the regioselectivity and endo/exo selectivity of this reaction is attributed to intermolecular hydrogen bonding between the hydroxyl group of the diene and the carbonyl oxygen atoms at C-4 and C-5 of the quinone in t he transition state. The possible transition states have been modelled by A MI calculations in order to better interpret these experimental results. (C ) 1998 Elsevier Science Ltd. All rights reserved.