摘要：

A new, regiospecific [3 + 2] annulation approach to highly substituted 5-membered carbocycles has been developed. The "TMS-cyclopentene annulation" involves the reaction of (trimethylsilyl)allenes with electron-deficient alkenes and alkynes in the presence of titanium tetrachloride to afford, in a single step, a functionalized and highly substituted TMS-cyclopentene derivative. Annulations employing , β-unsaturated ketones proceed stereoselectively via suprafacial addition to the enone. Some useful transformations of the annulation products are also described; for example, treatment with K 2CO 3-methanol or HF in acetonitrile effects isomerization and desilylation yielding ,β-unsaturated ketones.

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