A versatile synthetic route to 1,5-dithiocins from <i>o</i>-mercapto aromatic aldehydes

An earlier procedure for the facile preparation of benzo-fused 1,5-dithiocins 2a-2c from o-mercapto- benzaldehydes has been improved and shown to be capable of extension to the preparation of several naphthalene-derived analogues. The general method also afforded several N-alkylated 1,5-dithiocins 4, 5 by replacing NH 3 with the appropriate primary amine. It was found that N-acylation of the 1,5-dithiocins was successful only with methyl chloroformate. Attempted N-phenylation met with limited success but was shown to be unnecessary since even the less reactive aniline readily undergoes the general reaction of primary amines. When simple α-amino acids, or their methyl esters, were employed as the primary amine in the reaction with o-mercaptobenzaldehyde, the formation of the N-alkylated 1,5-dithiocins 4a, 17a,17b with accompanying loss of -COOH or -COOMe was observed, in preparatively useful yields. A mechanism is proposed for this interesting transformation.Key words: 1,5-dithiocins, α-amino acids, N-acylation, decarboxylation.