Alcohols, configuration enantiomeric excess, determination

Enzymatic reduction of 23a with recLBADH and CPCR resulted in unsatisfactory results (60% and 49% ee) as well. The results mentioned above indicate that a bulky substituent at the alkyne moiety results in a higher selectivity of the reduction. Furthermore, Bradshaw et al. reported that Lactobacillus kefir ADH, an enzyme highly homologous to LB ADH, affords (R)-4-trimethylsilyl-3-butyn-2-ol [(R)-25j with an ee of 94% in 25% yield [39bj. In our investigations ketone 23b was reduced by recLBADH with almost quantitative conversion. The enantiomeric excess and absolute configuration of the product were determined by desi-lylation with borax converting alcohol (R)-25 into enantiopure (R)-3-butyn-2-ol [(R)-24j (Scheme 2.2.7.14). 

When allylic and homoallylic alcohols are subjected to hydroformylation, the product was obtained as a lactol, e.g., 3-phenyl-2-hydroxytetrahydrofuran (Scheme 12) [96]. Due to the relative configuration between the C-2 and C-3 carbons, it was formed as a 1 1 diastereomeric mixture. The enantiomeric excesses were determined by oxidizing the lactols into the corresponding lactones. 

To a solution of [Rh(cod)2]Bp4 (5.0 mg, 0.012 mmol) in MeOH (10 mL) in a glove box was added (, 5, 7 ,5)-Me-PennPhos (125) (0.15 mL of a 0.1-M solution in MeOH, 0.015 mmol). After the mixture was stirred for 30 min, the enol acetate 172 (1.2 mmol) was added. The hydrogenation was performed at room temperature under 1.7 atm of hydrogen for 24 h. After the hydrogen was released, the reaction mixture was passed through a short silica gel column to remove the catalyst. The enantiomeric excess of 173 was measured by capillary GC without any further purification. The absolute configurations of the product was determined by comparing the observed optical rotation with that of chiral acetate made from a readily available secondary alcohol. ... 

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