Versatile Asymmetric Synthesis of the Kavalactones: First Synthesis of (+)-Kavain
摘要:
Three asymmetric pathways to the kavalactones have been developed. The first method is chiral auxiliary-based and utilizes aldol reactions of N-acetyl thiazolidinethiones followed by a malonate displacement/decarboxylation reaction. The second approach uses the asymmetric catalytic Mukaiyama additions of dienolate nucleophile equivalents developed by Carreira and Sato. Finally, tin-substituted intermediates, prepared by either of these routes, can serve as advanced general precursors of kavalactone derivatives via Pd(0)-catalyzed Stille couplings with aryl halides.
Stereoselective aldol additions of titanium enolates of N-acetyl-4-isopropyl-thiazolidinethione
摘要:
The addition of chlorotitanium enolates of N-acetyl isopropyl thiazolidine-2-thione to aldehydes was investigated. The stereoselectivity of the aldol products was controlled by the number of equivalents of base added. The syn aldol product was obtained preferentially when 2 equiv of Lewis acid and 1 equiv of base were employed. The anti aldol product was obtained preferentially when 1 equiv of Lewis acid and 2 equiv of base were employed for unsaturated aldehydes. Unexpected results were found with hindered aldehydes when 2 equiv of base were employed. (C) 2004 Elsevier Ltd. All rights reserved.