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, Hisatoshi Konishi, Shuhei Fukamachi
2010 Heterocycles  
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,
more » ... (1H)-thiones and/or the ionic cyclization products, 4-ethylidene-1,4-dihydro-3,1-benzoxazine-2-thiones. INTRODUCTION We recently reported that !-substituted 2-isothiocyanatostyrenes, generated in situ by the treatment of the corresponding isocyanides with sulfur in the presence of a catalytic amount of selenium and excess triethylamine under Fujiwara's conditions, 1 underwent ECR to afford 4-substituted quinoline-2(1H)thiones. 2 As an extension of this sequence, we envisaged that the enolate forms of 2-isocyanatophenyl ketones would underwent ECR to give 4-hydroxyquinoline-2(1H)-thiones. In this report, we present the results of our investigation on reactivity of 2-isothiocyanatophenyl methyl ketones and ethyl 2-isothiocyanatophenyl ketones. The investigation has indicated that 2-isothiocyanatophenyl methyl ketones, derived from 2-isocyanophenyl methyl ketones, give the corresponding ECR products, 4-hydroxyquinoline-2(1H)-thiones, via their enolate forms, and that ethyl 2-isothiocyanatophenyl ketones gave ECR products, 4-hydroxy-3-methylquinoline-2(1H)-thiones, along with the ionic cyclization products, 4-ethylidene-1,4-dihydro-3,1-benzoxazine-2-thiones.
doi:10.3987/com-10-11991 fatcat:i7v7yjyitvfarpw72dmgqaldbq