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■ Cyclization Reactions of 2-Isothiocyanatophenyl Ketones Giving 4-Hydroxyquinoline-2(1H)-thiones and 4-Alkylidene-1,4-dihydro-3,1-benzoxazine-2-thiones

Kazuhiro Kobayashi,* Toshihide Komatsu, Shuhei Fukamachi, and Hisatoshi Konishi

*Department of Chemistry and Biotechnology, Graduate School of Engineering, Tottori University, 4-101 Koyama-minami, Tottori 680-8552, Japan

Abstract

2-Isothiocyanatophenyl methyl ketones, generated in situ by treatment of 2-isocyanophenyl methyl ketones with sulfur in the presence of a catalytic amount of selenium and excess triethylamine, underwent electrocyclic reaction (ECR) via their enolate forms to give 4-hydroxyquinoline-2(1H)-thiones. The reaction products from ethyl 2-isothiocyanatophenyl ketones generated in situ from the corresponding isocyanides under similar conditions proved to be the ECR products, 4-hydroxy-3-methylquinoline-2(1H)-thiones and/or the ionic cyclization products, 4-ethylidene-1,4-dihydro-3,1-benzoxazine-2-thiones.