Molecular iodine (10 mol%) efficiently catalyzes the ring expansion of 4‐oxoazetidine‐2‐carbaldehydes in the presence of tert‐butyldimethylsilyl cyanide, or allylic and propargylic trimethylsilanes to afford protected 5‐functionalized‐3,4‐dihydroxypyrrolidin‐2‐ones with good yield and high diastereoselectivity, through a C3C4 bond cleavage of the β‐lactam nucleus. Interestingly, in contrast to the iodine‐catalyzed reactions of 3‐alkoxy‐β‐lactam aldehydes which lead to the corresponding γ‐lactam derivatives (rearrangement adducts), the reactions of 3‐aryloxy‐β‐lactam aldehydes under similar conditions gave β‐lactam‐fused chromanes (cyclization adducts) as the sole products, through exclusive electrophilic aromatic substitution involving the C3 aromatic ring and the carbaldehyde. In order to support the mechanistic proposals, theoretical studies have been performed.

中文翻译：

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分子碘催化4-氧杂氮杂环丁烷-2-甲醛中环的扩环与环化：协同的实验和理论研究

在叔丁基二甲基甲硅烷基氰化物或烯丙基和炔丙基三甲基硅烷的存在下，分子碘（10摩尔％）可有效催化4-氧杂氮杂环丁烷-2-甲醛的扩环，从而提供受保护的5-官能化-3,4-二羟基吡咯烷酮-2-酮具有良好的收益率和高非对映选择性，通过C3 β-内酰胺核的C4键裂解。有趣的是，与3-烷氧基-β-内酰胺醛的碘催化反应生成相应的γ-内酰胺衍生物（重排加合物）相反，在相似条件下3-芳氧基-β-内酰胺醛的反应得到了β-内酰胺。内酰胺稠合的苯并二氢吡喃（环化加合物）是唯一的产品，通过涉及C3芳环和甲醛的独家亲电芳族取代。为了支持机械方案，已经进行了理论研究。