PERISELECTIVE INTRAMOLECULAR CYCLOADDITION OF ALLENYL THIOETHERS AND ALLENYL SULFONES

The thermal intramolecular cycloaddition reactions of variously substi tuted allenyl 3-vinyl-2-cyclohexenyl thioethers and sulfones and the b ase-catalyzed intramolecular cycloaddition reactions of several propar gyl 3-vinyl-2-cyclohexenyl thioethers have been investigated. When the re was no steric congestion in the transition state, the substrates ga ve 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 conforma tion of the butadiene moiety in the transition state, novel [2 + 2] cy cloadducts 4, 37, and 40 were obtained from allenyl sulfones, 1b, 25, and 27, and allenyl thioether 20b underwent a tandem [2 + 2] cycloaddi tion/[3,3]-sigmatropic rearrangement reaction sequence to produce 30 a s 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 structur e of [2 + 2] adduct 4 was confirmed by single-crystal X-ray analysis t o be a strained tricyclic containing 4-, 5-, and 6-membered rings.