Stereoselective Construction of Methylenecyclobutane-Fused Indolines through Photosensitized [2+2] Cycloaddition of Allene-Tethered Indole Derivatives

• DOI: 10.1021/acs.orglett.9b00309
• Publication Date: 2019-02-21T16:07:41Z
• Authors: Noriyoshi Arai; Takeshi Ohkuma
• Keywords: Allene

Irradiation of 1-(hexa-4,5-dienoyl)indole derivatives in the presence an aromatic ketone by a high-pressure mercury lamp through Pyrex glass gave corresponding cyclized products stereoselectively high yields. The major part was all- cis-fused methylenecyclobutane-type compound produced [2+2] cycloaddition, accompanied small amounts alkynes via 1,5-hydrogen transfer biradical intermediate. Among range ketones, 3',4'-dimethoxyacetophenone found to sensitize substrate quite effectively.