A Facile Method for the Synthesis of Oxoketene-N,S- and -N,N-acetals from Reactions of Amino Compounds

2-Aroyl-3,3-bis(alkylsulfanyl)acrylaldehydes reacted with various primary amines, namely, o-phenylenediamine, ethylenediamine, and anilines to produce functionalized oxoketene-N,S-acetals and N,N-acetals in good yields. Imidazolo derivatives synthesized with o-phenylenediamine and ethylenediamine containing a formyl group could act as valuable starting materials for a variety of substituted heterocyclic compounds. 1. Introduction Oxoketene-N,S- and -N,N-acetals are highly versatile synthons for heterocyclic synthesis [1–3]. They are quite stable and can be stored indefinitely without any decomposition. They exhibit the nucleophilic displacement reactions by various binucleophiles followed by intramolecular cyclisation leading to the formation of cyclic compounds, and such reactions are characteristics of enamines [1–3]. Junjappa and coworkers prepared a series of functionalized heterocycles by treating them with binucleophiles like hydrazines, hydroxylamines, guanidines, cyanoacetamides, and so forth, [4–6]. They have also prepared functionalized quinolines from α-oxoketene-N,S-acetals employing Vilsmeier-Haack reaction [7]. A similar strategy was reported for the synthesis of quinoxalines from nitroketene-N,S-acetals, important benzoheterocycles displaying a broad spectrum of biological activities [8]. Our research group has also made attempts to explore the synthetic utility of oxoketene-N,S-acetals derived from thioamides [9]. We have shown that their reactions with α-halo ketones or ethyl bromoacetates afford amino thiophenes [10]. The α-oxoketene-N,S-acetals are generally prepared by the direct amination reactions of oxoketene-S,S-acetals by appropriate amines which resulted in a mixture of oxoketene-N,S-acetals and -N,N-acetals in most of the cases. They have also been synthesized directly from active methylene ketones by treating them with phenyl isothiocyanate followed by alkylation. We envisioned that the 2-aroyl-3,3-bis(alkylsulfanyl)acrylaldehydes 2 which we had reported recently could be transformed into aroyl formyl ketene-N,S-acetals or aroyl formyl ketene-N,N-acetals by direct amination reaction. The literature survey shows that such formyl ketene-N,S-acetals and formyl ketene-N,N-acetals have not been reported so far, and such compounds will be established in near future as valuable pivot for a variety of amino substituted heterocyclic compounds. Therefore, it appeared worthwhile to utilize 2-aroyl-3,3-bis(alkylsulfanyl)acrylaldehydes for the synthesis of those synthons. In this paper, we report the reactions of 2-aroyl-3,