Regioselectivity in the Cycloaddition Reactions of t-Butyl Trimethylsilyl Thioketone with 1,3-Butadienes

Regioselectivity in the Cycloaddition Reactions of t-Butyl Trimethylsilyl Thioketone with 1,3-Butadienes

Thermal cycloaddition of t-butyl trimethylsilyl thioketone (1) with 2-substituted dienes such as isoprene and 2-trimethylsilyloxy-1,3-butadiene occurred smoothly at 80${\circ}C$ to afford regioiomeric mixtures of cycloadducts. On the other hand, similar treatment of 1 with 1-substituted dienes such as trans-1,3-pentadiene, 1-methoxy-and 1-acetoxy-1,3-butadiene and Danishefsky's diene afforded a single regioisomeric adduct, respectively. Protodesilylation of the silylated adducts 8 and 11 could also be performed with ease.

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