Enantiomericallypure P-tolyl sulphinyl-N,N-dimethylthioacetamide (1) was prepared starting from (-)-(S)-menthyl toluene-p-sulphinate. Aldol-type condensation of (1) and subsequent removal of the Sulphinyl group open an entry to optically active β-hydroxy thioacetamides in 40–90% e.e.
under conventional basic conditions. A hard Lewis basic phosphine oxide has emerged as an effective additive to constitute a highly active ternary soft Lewisacid/hard Brønsted base/hard Lewis base cooperative catalyst, enabling a direct enantio- and diastereoselective aldol reaction of thiopropionamides. Strict control of the amount of the hard Lewis base was essential to drive the catalytic cycle
A directcatalyticasymmetricaldolreaction of thioamides with a soft Lewis acid/hard Brønsted base cooperative catalytic system comprising (R,R)-Ph-BPE/[Cu(CH(3)CN)(4)]PF(6)/LiOAr is described. Highly chemoselective deprotonative activation of thioamides allows for a directaldolreaction of alpha-nonbranched aliphatic aldehydes, which are susceptible to self-condensation. Facile reduction of the