氮杂环丙烷与给体-受体环丙烷的 Nazarov 环化和串联 [4 + 2]-环加成反应。
Nazarov Cyclization and Tandem [4 + 2]-Cycloaddition Reactions of Donor-Acceptor Cyclopropanes.
机构信息
Department of CPC (Organic Chemistry-II), ‡Centre for NMR and Structural Chemistry, §Centre for X-ray Crystallography, CSIR-Indian Institute of Chemical Technology , Hyderabad-500007, India.
出版信息
Org Lett. 2017 Sep 1;19(17):4500-4503. doi: 10.1021/acs.orglett.7b02061. Epub 2017 Aug 18.
The development of aryl vinyl/divinyl donor-acceptor cyclopropanes (DACs) as novel Nazarov cyclization (NC) precursors is described. The 1,3-zwitterion, generated from DACs embedded in the divinyl framework, acts as a pentadienyl cation, a requisite for Nazarov cyclization. A cyclic allyl cation in the course of NC was trapped with external nucleophiles to provide an interrupted NC product. Indeed, an allyl cation in this reaction is analogous to a 1,4-zwitterion that on reaction with dipolarophiles provided an easy access to substituted pyrans with excellent yield and diastereoselectivity via NC followed by a formal [4 + 2] cycloaddition.
本文描述了作为新型纳扎罗夫环化（NC）前体的芳基乙烯基/二乙烯基给体-受体环丙烷（DAC）的发展。嵌入在二乙烯基骨架中的 DAC 生成的 1,3-两性离子作为纳扎罗夫环化所需的戊二烯阳离子发挥作用。NC 过程中的环状烯丙基阳离子被外部亲核试剂捕获，以提供中断的 NC 产物。实际上，该反应中的烯丙基阳离子类似于 1,4-两性离子，其与偶极体反应通过 NC 提供了易于获得的取代吡喃，收率和非对映选择性极好，随后是通过[4 + 2]环加成的形式。
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