中文摘要：

重点从立体选择性和催化机理方面,总结了不同的有机小分子催化剂在烯酮的[2＋2]和[4＋2]不对称环加成反应中的应用.

英文摘要：

In this review,organocatalytic asymmetric [2＋2] and [4＋2] cycloaddition reactions of ketenes are summarized with emphasis on the selectivities and mechanisms of different catalysts.