Remote Stereocontrol in Acyclic Systems. Hydride Addition to 1,5- and 1,6-Hydroxy Ketones Mediated by Metal Chelation.

Acyclic 1,6-hydroxy amino ketones can be reduced to either the anti or syn diols with high 1,6 diastereoselectivity by sequential treatment with a Lewis acid and a borohydride reagent, with the direction of stereocontrol depending on the Lewis acid complexant used. For example, with 1a anti:syn ratios of >100:1 [Ti(OiPr)4/K-Selectride] and 1:7 [Al(OEt)3/K-Selectride] were realized. 1,5-Hydroxy amino ketone 4a was reduced with high syn 1,5 diastereoselectivity [anti:syn = 1:18 with Al(OEt)3/K-Selectride].