American Chemical Society
ja7b05277_si_002.cif (298.46 kB)

Intramolecular Crossed [2+2] Photocycloaddition through Visible Light-Induced Energy Transfer

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posted on 2017-07-06, 00:00 authored by Jiannan Zhao, Jonathan L. Brosmer, Qingxuan Tang, Zhongyue Yang, K. N. Houk, Paula L. Diaconescu, Ohyun Kwon
Herein, we present the intramolecular [2+2] cycloadditions of dienones promoted through sensitization, using a polypyridyl iridium­(III) catalyst, to form bridged cyclobutanes. In contrast to previous examples of straight [2+2] cycloadditions, these efficient crossed additions were achieved under irradiation with visible light. The reactions delivered desired bridged benzobicycloheptanone products with excellent regioselectivity in high yields (up to 96%). This process is superior to previous syntheses of benzobicyclo[3.1.1]­heptanones, which are readily converted to B-norbenzomorphan analogues of biological significance. Electrochemical, computational, and spectroscopic studies substantiated the mechanism of triplet energy transfer and explained the unusual regiocontrol.