Synthesis of Optically Active Orgnoantimony Compounds and Their Application for Asymmetric Reactions

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Transition metal-catalyzed asymmetric reactions with enantiopure ligands have been of much interest for synthetic chemists because of their wide applicability in the synthesis of a variety of biologically active compounds. Despite remarkable usefulness as a chiral inducer of phosphorous and arsenic ligands in asymmetric synthesis, however, asymmetric reactions with optically active organoantimony ligands have not been reported so far due to the limited access to this class of compounds. In these points of view, we planed to establish a versatile route for the synthesis of optically active organoantimony compounds and to investigate their potential for chiral inducer in asymmetric reactions.1.Synthesis of Optically Active C_2-Chiral Organoantimony Compounds and Their Use for Asymmetric ReactionsRacemic C_2-Symmetrical 2,2'-diarylstibano-1,1'-binaphthyl (BINASb:1), C_2-unymmetrical 2-diarylstibano-2'-dipheny phosphano-1,1'-binaphthyl (BINAPSb:2), 2-diarylstibano-2'-dimethylamino-1,1'-bin … More aphthyl (MASb:3) has been prepared from (±)-2,2'-dibromo-1,1'-binaphthyl and they could be successfully resolved in enantiopure form via separation of diastereomeric mixture of the Pd-complex arose from the reaction with optically active palladium reagent such as di-μ-chlorobis{(S)-2-[1-(dimethylamino)ethyl]phenyl-C^1,N}dipalladium(II). Research on several asymmetric reactions, such as asymmetric reduction of prochiral ketones (Reaction 1), allylic alkylation of allyl acetate (Reaction 2), and hydrosilylation of styrene (Reaction 3) by use of these organoantimony ligands as chiral auxiliaries revealed that BINASb (1) was a useful ligand for the Reaction 2 and BINAPSb (2) had high potential for the reaction 3. In the latter reaction, BINAPSb (2) should function as bidentate ligand at the early stage of the reaction and as monodentate ligand at the last stage.2.Synthesis of Optically Active C-Chiral and Sb-Chiral Organoantimony Compounds Bearing Benzylamine and Oxazoline Moieties and Their Use for Asymmetric ReactionsThe title compounds, C-chiral (S)-(α-methyl-2-di-p-tolylstibanobenzyl)dimethylamine (AMSb:4) and its chromium complex (AMSb-Cr:5), and C- and Sb-chiral Sb(R/S)-(aryl)[2-(S)-(1-dimethylaminoethyl)phenyl](p-Tolyl)stibane (6) has been synthesized from common (S)-(α-methylbenzyl)dimethylamine. Similar synthetic route could be applied to the synthesis of C(S),Sb(R/S)-aryl[2-(2-oxazolino)phenyl](p-tolyl)stibane (7) from (S)-4-isopropyl-2-phenyl-2-oxazoline. The asymmetric reactions by use of these ligands showed that the compound 7 was effective for the Reaction 2, although the other ligands (4〜6) had modest ability as chiral auxiliary for these asymmetric reactions. Less