Kinugasareactions between chiral acetylenes and five-membered nitrones, achiral and bearing a stereogenic center in both enantiomeric forms, proceed in moderate to good yield with high diastereoselectivity affording mostly one dominant product. The first step of the reaction is controlled by the configuration of the nitrone, whereas the protonation of intermediate enolate in the second step depends
An expedient method for the stereoselective preparation of alk-2-yne-1,4-diols has been achieved, based on the addition of chiral alk-1-yn-3-ols (or their protected derivatives) to aldehydes mediated by zinc triflate, Et3N, and (+)- or (–)-N-methylephedrine. In general, the configuration observed at the emergent stereocenter depends on the N-methylephedrine employed resulting in good to excellent
Enantioselective hydrogenation of alkynyl ketones catalyzed by Ru(OTf)(TsDPEN)(eta(6)-p-cymene) (TsDPEN = N-(p-toluenesulfonyl)-1,2-diphenylethylenediamine) affords the propargylic alcohols in up to 97% ee. The alkynyl moieties are left intact In most cases. The reaction can be conducted with a substrate-to-catalyst molar ratio as high as 5000 under 10 atm of H-2. The mode of enantioselection is elucidated with the transition state models directed by the CH/pi attractive interaction between the substrate and the catalytic species.