Direct synthesis of dithioketals from N,N-dialkylhydrazones

Direct dithioketalisation of N,N-dialkylhydrazones promoted by BF3. Et2O or p-TsOH and 1,2-ethanedithiol in dry medium affords the corresponding dithiolanes in nearly quantitative yields. A variety of hydrazones derived from several kinds of aldehydes (aliphatic, aromatic, and alpha,beta-unsaturated) and hydrazines [N, N-dimethylhydrazine, 1-aminopyrrolidine, and (S)-1-amino-2- (methoxymethyl)pyrrolidine (SAMP)] were reacted, indicating the generality of the method. The reaction was demonstrated to proceed without racemization of a particularly sensitive chiral substrate. (C) 1998 Elsevier Science Ltd. All rights reserved.