Cycloadditions and Cyclizations of Acetylenic, Allenic, and Conjugated Dienyl Sulfones

The cyclizations and cycloadditions of unsaturated sulfones containing more than one carbon-carbon π-bond was studied. Numerous Diels-Alder reactions have been reported that successfully exploit the activating effect of the sulfone group upon the reactivity of dienophiles in cycloadditions with normal electron demand. An experiment conducted by Glass and Smith and later by Hanack demonstrated the high Diels-Alder reactivity of perfluoroalkyl acetylenic sulfones. The rate constants for the reactions of the trifluoromethyl derivative 6a with dienes were greater than for acetylenes activated by carbonyl or nitrile groups. Shen and Schultz aromatized the cycloadduct obtained from 1,3-pentadiene and acetylenic sulfone 20 by either dehydrogenation with NiO 2 or elimination of benzenesulfinic acid. It is noteworthy that 20 displayed higher reactivity than dimethyl acetylenedicarboxylate, thus demonstrating the stronger activating effect of the sulfonyl group compared with that of an ester substituent.