Stereoselective one-pot synthesis of multi-substituted (2Z,4E)-2,4-dienamides from ketene dithioacetal and their solid-state fluorescence

Multi-substituted conjugated dienes are useful intermediates for the synthesis of various biologically active compounds and functional materials. In this study, one-pot synthesis of multi-substituted 2,4-butadienes was achieved via the reaction of ketene dithioacetal, 3,3-bis(methylsulfanyl)methylenemalononitrile ( 1 ), with a variety of aromatic ketone compounds. Complete stereoselective (2 Z ,4 E )-2,4-dienamide ( 3a ) was obtained from 1 with 4-methoxyacetophenone ( 2a ) in the presence of sodium hydroxide as a base in DMSO. Similarly, the reaction of 1 with electron-rich aromatic ketones or heterocyclic aromatic ketones gave (2 Z ,4 E )-2,4-dienamide compounds as the sole product in 31–61 yields. In the proposed synthetic sequence, the process consists of a cascade reaction involving the addition of 1 to ketone compound, elimination of methylthiolate anion from 1 , subsequent intramolecular cyclization and ring opening reaction by readdition of methylthiolate anion. Moreover, all the (2 Z ,4 E )-2,4-dienamide compounds ( 3a – j ) obtained in this study exhibited blue-green fluorescence in the solid state, which suggested the possibility of obtaining functional conjugated dienes by this novel one-pot synthetic method.