Biaryl hydroxy aldehydes as intermediates in the metal-assisted atropo-enantioselective reduction of biaryl lactones: Structures and aldehyde-lactol equilibria
作者:Gerhard Bringmann、Matthias Breuning、Heike Endress、Daniel Vitt、Karl Peters、Eva-Maria Peters
DOI:10.1016/s0040-4020(98)00618-8
日期:1998.9
The synthesis of substituted 1-(2'-hydroxyphenyl)naphthalene-2-carbaldehydes 4 and 6-alkoxy-6H-pyrans 7 and 8, analogs of the postulated metallated intermediates in the atropo-enantioselective ring cleavage of configuratively unstable biaryl lactones 2, is described. While the equilibria between the open hydroxy aldehydes 4 and the cyclic lactol structures 3 are completely shifted towards 4 for the derivatives 4c-g with substituents ortho to the biaryl axis, the lactol forms are the dominating structures (ca. 50-100%) for the ortho-unsubstituted compounds. For the lactols 3 and their acetalic analogs 6, 7, and 8, those diastereomeric conformations are preferred (77-100%) that have the exo-oxygen function axial. (C) 1998 Elsevier Science Ltd. All rights reserved.