Novel Synthesis of 4H‐Quinolizine Derivatives Using Sulfonyl Ketene Dithioacetals

Abstract

AbstractIn the synthesis of 4H‐quinolizine derivatives involving the use of a sulfonyl ketene dithioacetal, we found a novel reaction in which the remaining methylsulfanyl group was replaced with a proton after the ring‐closure reaction in the quinolizine skeleton under mild conditions, without the use of any metallic reagent. The reaction of 3,3‐bis(methylsulfanyl)‐2‐phenylsulfonylacrylonitriles (1a,b) with 2‐pyridylacetonitrile (2a) in the presence of potassium carbonate as a base in DMSO afforded 4‐imino‐2‐methylsulfanyl‐3‐phenylsulfonyl‐4H‐quinolizine‐1‐carbonitriles (3a,b). The methylsulfanyl group at the 2‐position of 3a,b was readily removed under methanol reflux conditions to afford 4‐imino‐3‐phenylsulfonyl‐4H‐quinolizine‐1‐carbonitriles (4a,b) in good yields. Alkyl 3‐phenylsulfonyl‐4H‐quinolizine‐1‐carboxylates (4c–f) were directly synthesized from sulfonyl ketene dithioacetal (1a,b) with alkyl 2‐pyridylacetates (2b,c) and involved desulfanylation by simple hydrolysis. In addition, the fluorescent properties of these compounds were investigated. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2009)