Utilization of industrial waste materials, 5. Synthesis of new, chiral 1,3,2‐oxazaphospholidine‐borane complexes and attempts to apply them in the stereoselective synthesis

Abstract

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.

P(III)-Chirogenic Phosphinite Building Blocks by Stereospecific N→O Phosphinyl Migration

“…When oxazaphospholidine-borane complexes 10 reacted with organolithium reagents (R 2 Li), the corresponding aminophosphine-boranes 7 were obtained by ring opening reaction upon P–O bond cleavage and were isolated as air-stable and storable diastereomerically pure compounds. ,− The reagents, structures, 31 P NMR chemical shifts, and isolated yields of the aminophosphine-boranes 7 are summarized in Table . Thus, the reaction of alkyl or aryllithium reagents with the oxazaphospholidine-borane complexes 10a – d leads to the diastereomerically pure aminophosphine-boranes 7a – s with yields reaching 97% (Table , entries 1–19).…”

l‐Menthol‐Assisted Synthesis of P‐Stereogenic Phosphinous Acid Amides and Phosphine‐Boranes

“…It is known that P–O bond cleavage in phosphinous acid‐borane esters proceeds with retention of configuration at the phosphorus atom when the reaction is carried at low temperature . Based on this, the absolute configuration at phosphorus for compounds 19a – 19g was assigned as R P , and for compound 19h as S P .…”

Phosphinous Acid-Boranes

“…The assignment of the absolute configuration to the resolved enantiomers of 2k was based on a chemical correlation [13], and was also unequivocally confirmed by a single-crystal X-ray diffraction study of the cinchonine salt [10,18]. The other resolved phosphinous acid-boranes 2b,c,n were assigned their absolute configurations as (S), by chemical correlations with the respective methyl phosphiniteboranes of known configurations [20][21][22][23] (eq. 37).…”