作者:Paul R. Carlier、Kam Moon Lo、Michael M.-C. Lo、Priscilla C.-K. Lo、Cedric W.-S. Lo
DOI:10.1021/jo9702148
日期:1997.9.1
In an effort to further optimize and to define the structural limitations of the nitrile aldol reaction, several studies were undertaken. Lithiated phenylacetonitrile 1 was demonstrated to exhibit diastereoselectivity for addition to benzaldehyde higher than that of other metalated phenylacetonitriles. With a view toward practical lab-scale synthesis of aldols derived from lithiated arylacetonitriles, the effects of reaction concentration and quenching method on isolated yields of the anti-aldols were readdressed. Secondary aldehydes give reasonable recrystallized yields of anti-aldols at reaction concentrations as high as 0.1 M; pivalaldehyde gives good results at concentrations up to 0.3 M. Thirdly, the aldol reaction of lithiated 1 with para-substituted benzaldehydes 6b-g was then studied; increasing electron-withdrawing power of the para substituent was found to cause a marked decrease in diastereaselectivity. Finally, the aldol reactions of two aliphatic nitriles (isovaleronitrile 4 and tert-butylacetonitrile 5, were studied. Suprisingly, aldol diastereoselectivity of aliphatic nitriles is not uniformly anti-selective, and selectivities overall are lower than those afforded by arylacetonitriles.