ISSN:
0947-3440
Keywords:
Phosphonates, α-hydroxyarylmethyl, α-, β- and γ-Hydroxyalkyl-
;
2-n-Butyloxazaborolidine catalysis
;
Enantioselective reduction
;
Keto phosphonates
;
Chemistry
;
Organic Chemistry
Source:
Wiley InterScience Backfile Collection 1832-2000
Topics:
Chemistry and Pharmacology
Notes:
The enantioselective synthesis of α-hydroxyarylmethylphosphonates 2a-p by the oxazaborolidine-catalyzed reduction of α-keto phosphonates 1a-p using different boranes 4a-c was studied in detail. Moderate to good enantioselectivities are found (up to 80% ee) by using the borane-dimethyl sulfide complex 4a as reducing reagent and the 2-n-butyl derivative of the (S)-5,5-diphenyl-3,4-trimethylene-1,3,2-oxazaborolidine catalyst 3b. In contrast, excellent enantiomeric excesses (up to 99% ee) as well as high chemical yields are obtained when catecholborane 4c in combination with low temperature is introduced. Substituent effects on the starting material 1 are discussed with the help of structural information obtained by X-ray analyses of the benzoylphosphonates 11fγ, 1jγ, and 1nγ. A slight decrease in enantioselectivity was found within the series of α-, β-, and γ-hydroxyalkylphosphonates 6, 8, and 10, respectively. Nevertheless, even these compounds are reduced with enantioselectivities ranging from 68% (10) to 95% (6) by using catecholborane 4c and catalyst 3b. On the other hand, we synthesized the allylic α-hydroxyphosphonate 12 in 75% chemical yield and with 56% enantiomeric excess by means of this methodology. The reaction has subsequently been applied to the synthesis of α-hydroxyalkylphosphonates 14a-c, which were obtained with ee values up to 90%. Compounds 14 are useful precursors for the synthesis of the P-amino acids 15.
Additional Material:
6 Tab.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1002/jlac.1995199511276
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