Polarized ketene dithioacetals. Part 65. Studies on additions of 2-aroyl-3-cyano-1,1-bis(methylthio)propenide anions to hetero-multiple bonds

Abstract

2-Aroyl-3-cyano-1,1-bis(methylthio)propenide anions (2a and b) undergo stepwise [3 + 2] cyclocondensation with aryl isothiocyanates followed by elimination of a methylthio group to give the corresponding 4-aroyl-2-arylamino-5-(methylthio)thiophene-3-carbonitriles (5a–c). Addition of the anion (2a)(Ar = Ph) to 4-chlorobenzaldehyde under similar conditions yielded the cyclic hemiacetal (8), which in the presence of BF₃· Et₂O and methanol afforded the O-methyl derivative (12) and 2-(4-chlorophenyl-3-bis(methylthio)methyl-5-phenylfuran-3-carbonitrile (13). Addition of the propenide anions (2a and c) to benzonitrile gave only dimeric products (14a and b), respectively. Mechanisms for these reactions are suggested.