85392-39-8Relevant articles and documents
THE ALDOL-TYPE CONDENSATION OF LITHIUM, BORON AND TITANIUM ENOLATES OF ISOCARANYL ACETATES WITH BENZALDEHYDE. THE METAL AND CHIRAL AUXILIARY EFFECTS
Fringuelli, Francesco,Piermatti, Oriana,Pizzo, Ferdinando,Scappini, Anna Maria
, p. 195 - 200 (2007/10/02)
A new approach to chiral enolates by using a chiral ester (isocaranyl acetates) and a chiral organometallic reagent (boranes and titanates) is reported.The effect of this double enantiodifferentiation and the effects of the isomerism of chiral auxiliary (2- and 4-isocaranyl) and that of the metal (Li, B, Ti) on the enantioselectivity of aldol condensation of 2- and 4-isocaranyl acetates with benzaldehyde are discussed.Lithium and boron enolates of isocaranyl acetates add preferentially to the si-face of benzaldehyde while the addition of analogous titanium enolates occurs preferably on the re-face of the aldehyde.The enolborinate which gives the highest ee value is that obtained by transmetallation reaction of the lithium enolate of (+)-2-isocaranyl acetate with (-)-di-4-isocaranylchloroborane.Obversely the enoltitanate prepared from (-)-4-isocaranyl acetate and the LDA-(+)-di-2-isocaranoxy(chloro)cyclopentadienyl titanate system is that which gives the highest enantiofacial discrimination.The chiral auxiliary effect has been used to plan the synthesis of (+)-4α-acetoxy-3β-trimethylsilyloxy-trans-carane, the titanium enolate of which gives (R)-(+)-β-hydroxy-β-phenylpropionic acid in high enantiomeric excess.
