Although the Nazarov cyclization is a widely used method for the synthesis of cyclopentyl ring systems, the lack of a general strategy for production of enantiopure products from this reaction detracts from its synthetic utility. This proposal seeks to develop a general method for enantioselective organocatalytic Nazarov cyclizations through the use of a chiral secondary amine catalyst. The proposed strategy relies upon iminium activation of the divinyl ketone substrates followed by a torquoselective ring closure to generate a 2-aminoallyl cation intermediate, which can be trapped intramolecularly with a variety of nucleophilic alkenes or aryl groups. Structurally diverse and stereochemicalty complex fused and bridged polycyclic products may be accessed from achiral, acyclic components via this methodology. These products may serve as building blocks for a variety of cyclopentanoid and terpene natural products. ? ?
| Kunz, Roxanne K; MacMillan, David W C (2005) Enantioselective organocatalytic cyclopropanations. The identification of a new class of iminium catalyst based upon directed electrostatic activation. J Am Chem Soc 127:3240-1 |
