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Paper | Regular issue | Vol 65, No. 11, 2005, pp.2683-2692
Published online, 16th August, 2005
DOI: 10.3987/COM-05-10518
The First and Reliable Synthesis of Thieno[2,3-e][1,2,4]triazolo[1,5-c]pyrimidin-5(6H)-ones via Their [4,3-c] Compounds by Dimroth Rearrangement

Tomohisa Nagamatsu* and Shoeb Ahmed

*Faculty of Pharmaceutical Sciences, Okayama University, Tsushima-naka 1-1-1, Okayama 700-8530, Japan

Abstract

This paper describes a reliable and general synthesis of thieno[2,3-e][1,2,4]triazolo[1,5-c]pyrimidin-5(6H)-one (5a) and its 2-substituted derivatives (5b-i) as a novel ring system prepared by nimble isomerization of their [4,3-c] compounds (4a-i), which were produced by condensation of 4-hydrazinothieno[3,2-d]pyrimidin-2(1H)-one (12) with appropriate triethyl orthoesters or by oxidative cyclization of 4-(benzylidenehydrazino)thieno[3,2-d]pyrimidin-2(1H)- ones (13c-i). The [1,5-c] isomers (5a-c) were further prepared by condensation of 3-amino-4-imino-2-oxo-1,2,3,4-tetrahydrothieno[3,2-d]pyrimidine (16) with appropriate triethyl orthoesters as a synthetic method for a reliable structure of the tricyclic ring systems.