Modified Riemschneider reaction of 3-thiocyanatoquinolinediones

Abstract

The Riemschneider reaction of 3-thiocyanatoquinoline-2,4(1H,3H)-diones with conc. H ; 2SO ; 4 was investigated. Using different reaction conditions, 13 types of reaction products were isolated. Compounds bearing a Me, Et, or Bu group at C(3) afforded mainly [1,3]thiazolo[5,4-c]quinoline-2,4- diones and 1,9b-dihydro-9b-hydroxythiazolo[5,4-c]quinoline-2,4-diones. In the case of the 3-Bu derivatives of the starting compounds, C-debutylation was also observed. If a Bn group is present at C(3), rapid C-debenzylation of the starting thiocyanates occurred, yielding [1,3]oxathiolo[4,5-c]quinoline-2,4- diones, and mixtures of mono-, di-, and trisulfides derived from 4-hydroxy-3-sulfanylquinoline-2-ones. The reaction mechanism of all of the transformations is discussed. All new compounds were characterized by IR, ; 1H- and ; 13C-NMR, and EI and ESI mass spectra, and in some cases, ; 15N-NMR spectra were also used to characterize new compounds.