New, chiral 1,3,2-oxazaphospholidine-borane complexes rane complexes 5a-c. This is a further example of the utiliza3a-b and 8a-d were synthesized from the p-amino alcohols tion of the industrial waste material (all-R)-2-azabicyclola-b and 6a-d. The borane complexes 3, 8a, 8c, and 8d [3.3.0]octane-3-carboxylic acid. The catalytic efficiency of were allowed to react with different organolithium com-the chiral 1,3,2-oxazaphospholidine-borane complexes 3a, pounds and afforded the corresponding aminophosphane3b, and 8c was examined in the enantioselective borane reborane complexes 4a-c and 9a-g. Acid methanolysis of duction of some ketones.those complexes led to the formation of the phosphinite-boRhodium complexes of chiral phosphanes are important catalysts in the enantioselective homogeneous hydrogenation of C=C, C=N, and C=O bonds. Thus, rhodium-DI-PAMP catalysts are used for the technical synthesis of the pharmarcon (S)-Dopa [2]. Optically active phosphane ligands such as (o-methoxypheny1)methylphenylphosphane (PAMP) and 1,2-ethandiylbis[(o-methoxyphenyl)phenylphosphane] (DIPAMP) could easily be synthesized from the chiral methoxyphosphane-borane These enantiomerically pure alkoxyphosphane boranes could be prepared by diastereoselective synthesis of the 1,3,2-0xazapho-spholidine-borane complexes and their regio-and stereoselective ring opening with organolithium compounds.The application of an 1,3,2-oxazaphospholidine-borane complex as catalyst in the enantioselective borane reduction of prochiral ketones is known [4].In context with our studies of the utilization of industrial waste materials['], we used the enantiomerically pure P-aminoalcohol (all-R)-l[lal for the synthesis of the chiral methoxyphosphane-borane complexes 5a-b. This alcohol was prepared by the reduction of the nonutilizable enantiomerically pure (aZZ-R)-2-azabicyclo[3.3.0]octane-3-carboxylic acid benzyl ester, a waste material which was obtained in the synthesis of the ACE inhibitor ramiprilrSl by Hoechst AG.The diastereomerically pure 1,3,2-0xazaphospholidine (3S,4aR,6aR,7aR)-2 was prepared by the reaction of bis(diethy1amino)phenylphosphane with the bicyclic, rigid, proline-analogous p-amino alcohol. Treatment of (3S,4aR,6a-R,7aR)-2 with a solution of borane-THF complex afforded the diastereomerically pure 1,3,2-oxazaphospholidine-borane complex (3S,4aR,6aR,7aR)-3 which crystallized from methanol as colourless crystals.

New optically active p-amino alcohols, derived from various acyclic and cyclic amino acids with alkyl groups on the carbino1 carbon atom, were used in the enantioselective reduction of prochiral ketones. The attachment of alkyl groups to the nitrogen atom of the catalyst (R)-lb was shown to influence favorably the enantioselectivity of the addition of diethylzinc to benzaldehyde. In both cases the resulting secondary alcohols were obtained in moderate to high optical yields.The enantioselective reduction of carbonyl groups with a variety of ligands, modified by boron and aluminum hydridescl] and the nucleophilic addition of chelated organometallics to carbonyl compounds [2], are two of the most important asymmetric reactions.Recently, much attention was focused on the preparation of catalysts with a p-amino alcohol structural unit. Both functionalities of the p-amino alcohol react with the hydride to give the corresponding 0xazaborolidine[~1. Remarkably, most of the p-amino alcohols employed in the literature bear aromatic groups, especially on the carbinol carbon atom. Therefore, we investigated enantioselective reactions with p-amino alcohols bearing various alkyl groups on the carbinol carbon atom. The p-amino alcohols employed in this paper derive from (R)-phenylglycine [for (R)-la-g], (9-phenylalanine [for (S)-21, (59-homophenylalanine [for (9-31, (9-teut-leucine [for (S)-4b], and (9-indolinecarboxylic acid [for (S)-5b]. Remarkably, the catalyst (S)-4b is a purely aliphatic Acetophenone and a-chloroacetophenone were used as model substrates for the enantioselective catalytic reduction with borane.The reductions of these prochiral ketones with borane were catalyzed by the oxazaborolidines formed in situ from (R)-la-e to (59-5b and gave the secondary alcohols in chemical yields between 65 and 93%. The oxazaborolidines were not isolated.The results of the reduction of the model ketones with the oxazaborolidines generated from the p-amino alcohols (R)-la-e to (S)-5b are summarized in Table 1. The catalysts (R)-la-e afforded alcohols with (S) configuration and the ligands (S)-2 to (S)-Sb gave alcohols with (R) configuration. The reductions of acetophenone were carried out by using 2 or 10 mol-% of the catalysts mentioned above. In all cases the enantioselectivity increased by increasing the amount of the catalyst. The most satisfactory results were obtained with (R)-lb as catalyst for the reduction of aceto- phenone with borane (88% ee with 2 mol-% and 92% ee with 10 mol-% of catalyst). It is noteworthy that the reduction of acetophenone with borane with 2 mol-% of the p-amino alcohol (R)-ld bearing a phenyl group at the stereogenic center afforded the (S) alcohol with 86% ee. The same reaction with 2 mol-% of the benzyl-substituted pamino alcohol (59-2 gave the (R) alcohol with 78% ee.

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ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.