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 K₂CO₃-methanol or HF in acetonitrile effects isomerization and desilylation yielding ⇌,β-unsaturated ketones.

中文翻译：

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（三甲基甲硅烷基）环戊烯环化的范围和立体化学过程

已开发出一种针对高度取代的5元碳环的新的区域特异性[3 + 2]环空方法。“ TMS-环戊烯环化”涉及（三甲基甲硅烷基）丙二烯与缺电子的烯烃和炔烃在四氯化钛存在下的反应，从而一步得到官能化且高度取代的TMS-环戊烯衍生物。采用⇌，β-不饱和酮的环化通过表面上加成至烯酮选择性地进行。还描述了环形产品的一些有用的转换。例如，在乙腈中用K ₂ CO _3-甲醇或HF处理可异构化和去甲硅烷基化，生成⇌，β-不饱和酮。