Highly stereoselective approach to alk-2-yne-1,4-diols by oxazaborolidine-mediated reduction of alk-2-yne-1,4-diones.

We performed the borane-mediated reduction of a series of symmetrical alk-2-yne-1,4-diones (5) in the presence of the oxazaborolidine (R)-6 to afford (R,R)-alk-2-yne-1,4-diols ((R,R)-1) in good yields and high stereoselectivities (up to 99.9% ee). In some cases, the stereochemical purity of 1 was improved by a two-step process: (i) temporary transformation of 1 into its vic-dibromo derivatives 9, which allowed us to remove the minor meso isomer by chromatography, and (ii) regeneration of the enantioenriched diols 1 with SmI2.

2-Piperidino-1,1,2-triphenylethanol: a highly effective catalyst for the enantioselective arylation of aldehydes.

Here we report the use of 2-piperidino-1,2,2-triphenylethanol (5) as an outstanding catalyst for the ligand-catalyzed arylation of aldehydes. The use of 5 and a 2/1 mixture of Et(2)Zn/Ph(2)Zn provided the corresponding chiral diarylcarbinols with enantiomeric excess of up to 99% ee. The effect of temperature on the reaction enantioselectivity was studied and the inversion temperature (T(inv)) was determined to be 10 degrees C for reaction with p-tolylaldehyde.

Addition of diethylzinc to dicobalt hexacarbonyl complexes of alpha,beta-acetylenic aldehydes with virtually complete enantioselectivity. A formal synthesis of (+)-incrustoporin.

[reaction: see text] The addition of diethylzinc to dicobalt hexacarbonyl complexes of acetylenes mediated by (R)-2-piperidino-1,1,2-triphenylethanol takes place with very high enantioselectivity (96-99% ee) to afford the S enantiomers of dicobalt hexacarbonyl complexes of 1-alkynyl-1-propanols. The utility of this process is exemplified by the development of a short, highly enantioselective (99% ee) synthesis of unnatural incrustoporin.