Titanium enolates of thiazolidinethione chiral auxiliaries: versatile tools for asymmetric aldol additions.
[formula: see text] Asymmetric aldol additions using chlorotitanium enolates of thiazolidinethione propionates proceed with high diastereoselectivity for the "Evans" or "non-Evans" syn product depending on the nature and amount of the base used. With (-)-sparteine as the base, selectivities of 97:3 to > 99:1 were obtained for the Evans syn products with 2 equivalents of base and for the non-Evans syn when 1 equiv of base was employed. The thiazolidinethione auxiliaries are easily removed, and the aldol adducts can be readily transformed to various functional groups. Even direct reduction to the aldehyde with diisobutylaluminum hydride is possible.
Crimmins
M T
MT
Venable and Kenan Laboratories of Chemistry, University of North Carolina, Chapel Hill 27599, USA. crimmins@email.unc.edu
Chaudhary
K
K
D000447:Aldehydes / Q000737:chemistry; D002625:Chemistry, Organic / Q000379:methods; D007202:Indicators and Reagents; D013034:Sparteine / Q000737:chemistry*; D013237:Stereoisomerism; D013844:Thiazoles; D053778:Thiazolidines; D014025:Titanium
D000447:Aldehydes; D007202:Indicators and Reagents; D013844:Thiazoles; D053778:Thiazolidines; D013034:Sparteine; C005104:2-mercaptothiazoline; D014025:Titanium