Periselective Intramolecular Cycloaddition of Allenyl Thioethers and Allenyl Sulfones

Article abstract of DOI:10.1021/jo00086a010

The thermal intramolecular cycloaddition reactions of variously substituted allenyl 3-vinyl-2-cyclohexenyl thioethers and sulfones and the base-catalyzed intramolecular cycloaddition reactions of several propargyl 3-vinyl-2-cyclohexenyl thioethers have been investigated.When there was no steric congestion in the transition state, the substrates gave Diels-Alder (<4 + 2>) adducts.When a substituent was introduced at C(2) of the cyclohexene in such way as to disfavor the s-cis conformation of the butadiene moiety in the transition state, novel <2 + 2> cycloadducts 4, 37, and 40 were obtained from allenyl sulfones, 1b, 25, and 27, and allenyl thioether 20b underwent a tandem <2 + 2> cycloaddition/<3,3>-sigmatropic rearrangement reaction sequence to produce 30 as the major product.C(4)-substituted compounds 22a,b and 28 underwent Diels-Alder (<4 + 2>) reactions exclusively; C(6)-substituted allenyl thioethers 24a,b and 26 did not afford the cycloadducts.The structure of <2 + 2> adduct 4 was confirmed by single-crystal X-ray analysis to be a strained tricyclic containing 4-, 5- and 6-membered rings.