ChemInform Abstract: First Example of [3,3]‐Sigmatropic Rearrangement in the Series of 2‐(Prop‐2‐yn‐1‐ylsulfanyl)‐1,4,5,6,7,8‐hexahydroquinolines.

Abstract

We previously revealed [3,3]-sigmatropic rearrangement of 2-allylsulfanyl(selanyl)-substituted 1,4-dihydropyridines and 1,4,5,6,7,8-hexahydroquinolines into 3-allyl-2-thioxo(selenoxo)-1,2,3,4-hexahydropyridines and 3-allyl-2-thioxo-1,2,3,4,5,6,7,8-octahydroquinolines [1]. [3,3]-Sigmatropic rearrangement of 3-(prop-2-yn-1-ylsulfanyl)-substituted carboand heterocycles usually results in formation of fused 2-methylthiophene or thiopyran derivatives [2]. In the present communication we report for the first time on the alkylation of morpholinium 4-aryl-3cyano-7,7-dimethyl-5-oxo-1,4,5,6,7,8-hexahydroquinoline-2-thiolates Ia and Ib with prop-2-yn-1-yl bromide (II) with formation of 4-aryl-7,7-dimethyl-5-oxo2-(prop-2-yn-1-ylsulfanyl)-1,4,5,6,7,8-hexahydroquinoline-3-carbonitriles IIIa and IIIb which underwent regioselective [3,3]-sigmatropic rearrangement into 4-aryl-7,7-dimethyl-5-oxo-3-(propa-1,2-dien-1-yl)-2thioxo-1,2,3,4,5,6,7,8-octahydroquinoline-3-carbonitriles IVa and IVb on heating in boiling ethanol. The structure of compound IVa was determined by X-ray analysis, which will be reported elsewhere. Morpholinium 3-cyano-7,7-dimethyl-4-(2-nitrophenyl)-5-oxo-1,4,5,6,7,8-hexahydroquinoline-2thiolate (Ia) and morpholinium 4-(4-chlorophenyl)-3cyano-7,7-dimethyl-5-oxo-1,4,5,6,7,8-hexahydroquinoline-2-thiolate (Ib) were synthesized according to the procedure described in [3]. 7,7-Dimethyl-4-(2-nitrophenyl)-5-oxo-2-(prop-2yn-1-ylsulfanyl)-1,4,5,6,7,8-hexahydroquinoline-3carbonitrile (IIIa). Prop-2-yn-1-yl bromide (II), 0.09 ml (1.2 mmol), was added at 25°C to a suspension of 0.5 g (1.13 mmol) of morpholinium salt Ia in 10 ml of ethanol. The mixture was stirred for 3 h, and the precipitate was filtered off and washed with ethanol and hexane. Yield 0.36g (81%), yellow powder, mp 133°C. IR spectrum, ν, cm: 3442 (NH), 2209 (C≡N), 1614 (C=O). H NMR spectrum, δ, ppm: 0.80 s and 0.98 s (3H each, Me), 1.92 d and 2.14 d (1H each, 6-H, J = 16.0 Hz), 2.36 d and 2.41 d (1H each, 8-H, J = 16.0 Hz), 3.41 s (1H, ≡CH), 3.97 s (2H, SCH2), 5.28 s (1H, 4-H), 7.44 t (1H, Harom, J = 8.0 Hz), 7.54 d (1H, Harom, J = 8.0 Hz), 7.70 t (1H, Harom, J = 8.0 Hz), 7.80 d (1H, Harom, J = 8.0 Hz), 9.86 br.s (1H, NH).