Acylthiazolidinethiones, chiral

Acyliminium ions can be used in enantioselective additions with enolates having chiral auxiliaries, such as A-acyloxazolidi nones or A-acylthiazolidinethiones. 

Chiral acylthiazolidinethiones such as 26 can readily be prepared from commercially available amino acids in three steps12 (Scheme 2.2k). They have been employed as a synthetically useful auxiliary in diastereoselective aldol reactions.13 The magnesium-catalyzed aldol reaction of the thiazolidinethione 26.S with cin-namaldehyde afforded 27 as a major diastereomer in 87% yield. Interestingly, compound 27 is the opposite anti-aldol diastereomer to that seen with the oxa-zolidinone 23S. 

Similarly, MgBr2-Et20 was proved to be an effective catalyst in the di-astereoselective direct anti-aldol reaction of chiral AT-acylthiazolidinethiones in the presence of triethylamine and chlorotrimethylsilane. Grood yields (56-93%) and diastereoselectivities (up to 19 1) were obtained for a variety of N-acylthiazolidinethiones and unsaturated aldehydes (140). 

---