No abstract

The thermal intramolecular cycloaddition reactions of variously substituted allenyl 3-vinyl-2cyclohexenyl 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 ) 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, lb, 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. * CDCI3.1 Chemical shifts relative to TMS ( 0.00).1 Multiplicities: s, singlet; d, doublet; t, triplet; m, multiplet. d Coupling constants in hertz.

No abstract

Enantioselective Synthesis of an Oxa-Taxane Derivative via Tandem Intramolecular (2 + 2) Cycloaddition and (3,3)-Sigmatropic Rearrangement of Allenyl Ether. --(YEO, S.-K.; HATAE, N.; SEKI, M.; KANEMATSU, K.; Tetrahedron 51 (1995) 12, 3499-3506; Inst. Synth.

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