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Nazarov Cyclization and Tandem [4 + 2]-Cycloaddition Reactions of Donor-Acceptor Cyclopropanes
Gangarajula Sudhakar1, S K Mahesh1, S Phani Babu Vemulapalli1
1Department 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.
Abstract:
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.
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