Acyclic stereoselection. 11. Double stereodifferentiation as a method for achieving superior Cram's rule selectivity in aldol condensations with chiral aldehydes

Article abstract of DOI:10.1021/jo00320a014

Double Stereodifferentiation (double asymmetric induction) can be used to alter the effective diastereoface selectivity (Cram's rule selectivity) in additions to chiral aldehydes. The method has been demonstrated by the reactions of ketones 5 and 6 with the two enantiomers of glyceraldehyde acetonide (46 and 47) and also by the reaction of ketone 65 with aldehyde 46 with the two enantiomeric 1,2,3,4-tetramethoxybutanes 63 and 64 as solvents. In the former case, significant alteration of the Cram's rule selectivity is observed. With ketone 5, the two erythro aldols are produced in a ratio of 1:1 with aldehyde 46 and 7:1 with aldehyde 47. With ketone 6, the double Stereodifferentiation effect is greater; the two erythro aldols are formed in a ratio of 2:1 from aldehyde 46 and in a ratio of >30:1 from aldehyde 47. Double Stereodifferentiation with the chiral solvents 63 and 64 is more modest. However, the effect is still observed, and 65 and 46 react to give the two erythro aldols in ratios of 5.0:1 or 3.6:1 when 63 or 64 is employed as solvent.