195433-98-8Relevant articles and documents
A General Strategy to Enantiomerically Pure Aliphatic and Olefinic Ketone Cyanohydrins by Stereoselective Alkylation of Umpoled Aldehyde Derivatives
Kirsten, Christian N.,Herrn, Michael,Schrader, Thomas H.
, p. 6882 - 6887 (2007/10/03)
We present the first general synthesis of optically pure (R)- and (S)-ketone cyanohydrins with olefinic and aliphatic substituents. Consecutive condensations of POCl3 with pseudoephedrine (1) and racemic crotonaldehyde cyanohydrin (3, R = 1-propenyl) lead to the respective cyanohydrin phosphate 4c. Deprotonation, followed by highly stereoselective alkylation and a single Chromatographic purification step, afford diastereomerically pure ketone cyanohydrin phosphates 5a-e. From these, enantiomerically pure tertiary cyanohydrins 6a-e can be obtained by mild Lewis acid-assisted hydrolysis. Pseudoephedrine is simultaneously recovered without loss of optical purity. The unsaturated alkylation products 5a-d are readily hydrogenated with diimide to aliphatic cyanohydrin phosphates 5f- i, which can be cleaved to furnish the free optically pure cyanohydrins 6f-i. Thus a broad variety of both saturated and unsaturated ketone cyanohydrins with R > Et becomes accessible in optically pure form for the first time. The free cyanohydrins are easily converted to optically pure α-branched α-hydroxy acids.
