Reaction of a brominated benzolactone/lactam with 4-methoxythiobenzamide and thiourea: an Eschenmoser coupling reaction, ring transformation, or dimerization?. Issue 20 (13th May 2015)

• Record Type: Journal Article
• Authors: Kammel, Richard; Tarabová, Denisa; Růžičková, Zdeňka; Hanusek, Jiří
• Is Part Of: Tetrahedron letters. Volume 56:Issue 20(2015)
• Page Start: 2548
• Page End: 2550
• Publication Date: 2015-05-13
• Subjects: Ring transformation -- Eschenmoser coupling reaction -- 3-Bromo-1, 3-dihydro-2H-indol-2-one -- 3-Bromo-1-benzofuran-2(3H)-one; Chemistry, Organic -- Periodicals; 547.005
• DOI: 10.1016/j.tetlet.2015.03.052
• Languages: English
• ISSNs: 0040-4039

Abstract

Graphical abstract: Abstract: The reactions of 3-bromo-1-benzofuran-2(3 H )-one (1a ) and 3-bromo-1, 3-dihydro-2 H -indol-2-one (1b ) with 4-methoxythiobenzamide and thiourea under mildly basic conditions are reported. While brominated lactone1a gave the expected 5-(2-hydroxyphenyl)-2-(4-methoxyphenyl)-1, 3-thiazol-4-ol (2 ) or 2-amino-5-(2-hydroxyphenyl)-1, 3-thiazol-4(5 H )-one (5 ) products, the analogous brominated lactam1b reacted with the thioamide via an unexpected Eschenmoser coupling reaction to give (3 Z )-3-[amino(4-methoxyphenyl)-methylidene]-1, 3-dihydro-2 H -indol-2-one (3 ). When lactam1b was treated with thiourea, isoindigo (4 ) was the only isolated product. The reaction mechanisms, involving formation of α-thioiminium or isothiouronium salts and their base-catalyzed decomposition are also proposed.