Polarized ketene dithioacetals. Part 26. Studies on base-catalysed rearrangements of 3,3-bis(alkylthio)-2-methyl-1-arylprop-2-en-1-ones and 3,3-bis(methylthio)-2-benzyl-1-phenylprop-2-en-1-one

Abstract

3,3-Bis(alkylthio)-2-methyl-1-arylprop-2-en-1-ones (1a-e) undergo facile rearrangement in the presence of sodium hydride in dimethylformamide to give the corresponding 3-alkylthio-2-alkylthiomethylacrylophenones (2a-e), respectively. Similarly 3,3-bis(methylthio)-2-benzyl-1-phenylprop-2-en-1-one (13) under similar conditions yielded the rearranged product, the chalcone (14) and the acrylophenone (15), in addition to two more products, β-methylthiochalcone (16) and the propenone (17). The mechanisms governing these transformations have been studied and it has been shown that the 1,3-RS shift in the dithioacetal intermediate (19) involves intermolecular participation of thiolate anion rather than a concerted process. A probable mechanism involving the solvent equilibrated enolate anion (27) formed by Michael addition of thiolate anion to (19) or the phenyl derivative (26) has been suggested for the rearrangement of (19) to the products (2) and of (26) to either compound (14) or (15). Also, the formation of products (16) and (17) is explained through oxidative cleavage of the carbanions (28) and (31) respectively.