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Please login to access the full content or check if you have access via Variation 4: By Reaction of a Tin Enolate with Nitrosobenzene

DOI: 10.1055/sos-SD-026-00761

Suffert, J.Science of Synthesis, (200526937.

The catalytic enantioselective introduction of an α-hydroxy group to a tin ketone enolate can be efficiently realized using nitrosobenzene in the presence of a Lewis acid catalyst (Scheme 98).[‌200‌] Chiral R-hydroxy ketones in up to 97% ee are obtained in high yields (6495%). The reaction is performed in the presence of 2,2-bis(diphenylphosphino)-1,1-binaphthyl or 2,2-bis(di-4-tolylphosphino)-1,1-binaphthyl [(R)-Tol-BINAP] and silver(I) trifluoromethanesulfonate to furnish the aminooxy ketone 211 with high O-selectivity. A small amount of the N-adduct is observed in some cases (119%) but generally the reaction is very selective, giving more than 99% of the O-adduct. Of the various silver salts surveyed, the trifluoromethanesulfonate and perchlorate provide superior levels in both asymmetric induction and regioselection. The transformation of R-aminooxy ketones 211 into the corresponding R-hydroxy ketones 212 is smooth and facile. For example, after reaction of nitrosobenzene with a cyclohexanone-derived tin enol ether, and the cleavage of the NO bond using a catalytic amount of copper(II) sulfate and excess methanol, (R)-2-hydroxycyclohexanone is obtained in 93% yield and 97% ee.

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