Periselective intramolecular cycloaddition of allenyl thioethers and allenyl sulfones
作者:Sin-Koo Yeo、Motoo Shiro、Ken Kanematsu
DOI:10.1021/jo00086a010
日期:1994.4
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(G)-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.