Asymmetric acetate aldol reactions in connection with an enantioselective total synthesis of macrolactin A

Asymmetric aldol-like reactions of cinnamaldehyde, dienal 3 (fragment C7-C12 of macrolactin A), and dienal 4 (fragment C15-C24) with (i) chiral acetylthiazolidinethione-derived enolates, (ii) chiral boron enolates, and (iii) silyl enolates in the presence of chiral titanium-2,2′-dinaphthol complexes are compared. Use of the thiazolidinethione auxiliary and TiCl 4 shows practical advantages; e.g., C5-C12 fragment 7 has been isolated enantiomerically pure in 74% yield.