Allenyl azide cycloaddition chemistry. 2,3-cyclopentennelated indole synthesis through indolidene intermediates
Ken S Feldman1, D Keith Hester, Malliga R Iyer
1Department of Chemistry, The Pennsylvania State University, University Park, Pennsylvania 16802, USA. ksf@chem.psu.edu
Abstract:
The thermal, photochemical, and photochemical/CuI-mediated cascade cyclizations of a range of substituted 1-(2-azidophenyl)-3-alkenylallenes are described. These reactions provide both 1,2- and 2,3-cyclopentennelated indole products in varying ratios. In most cases, high regioselectivity for the 2,3-annelated isomer can be achieved under the hnu/CuI conditions. Computational studies of this multistep reaction support the intermediacy of indolidene intermediates whose electrocyclizations (with or without copper present) define the regioselectivity branch point in the sequence.
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