| Research Abstract |
This study was performed to synthesize new Sb-chiral and C_2-symmetric optically active organoantimony (Sb) compounds and to clucidate their chemical propertics such as structural fcature, reactivity, and applicability as a chiral ligand to asymmetric syntheses.
1. Syntheses and resolutions of Sb-chiral and C_2-symmetric optically active organoantimony (III) compounds : (a) The most straightforward method for the preparation of group 15 organometallic compounds is the nucleophilic displacement of the halogen group on appropriate metal halides (R_nMX_<3-n, > M=P.As.Sb.and Bi) by treatment with Grignard or organolithium reagents. However, this method has been proved to be unsatisfactory for the preparation of M-chiral compounds, because the halogen moiety on R_nMX_<3-n> is highly reactive as leaving groups. To solve this problem, we used ethynyl groups instead of halogen groups, and found a new general method for the preparation of Sb-Chiral organoantimony compounds by stepwise nucleophil
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ic displacement of tribromostibane via a bisethynyl stibane intermediate. (b) Althought, the atropisomeric 1, 1-naphthyl core is the parent framework of a steadily increasing family of C_2-symmetric chiral auxiliaries of high efficiency and a variety of phosphorous and arsenic compounds, such as BINAP, MOP, BINAs, and BINAPAs have been reported, no optically active bismuth analogues have been known. We demonstrated that the reaction of 2, 2'-dilithio-1, 1'-binaphthyl intermediate, prepared from 2, 2'-dibromo derivative by treatment with t-BuLi, with metal dihalides (ArSbBr_2, ArBiBr_2) afforded the corresponding binaphthyl dedivatives (BINASb and BINABi) which can be resolved by use of optically active Pd-complex as a resolving agent. Otherwise, treatment of the optically active 2, 2'-dilithio-1, 1'-binaphthyl intermediate with ArSbBr_2 resulted in ring closure to afford optically active 7-aryldinaphtho[2, 1-b, 1', 2'-d] stiboles which is the first isolated example of optically active dinaphthoheterols.
2. Evaluation of optically active organoantimony (III) compounds for asvmmetric syntheses : Evaluation of the optically active organoantimony ligands obtained above for asymmetric reactions was made. The results show that the optically active organoantimony compounds were effective ligands for asymmetric reactions. such as transition metal catalyzed enantioselective reduction of prochiral ketones and asymmetric allylic substitution reaction of rac-1, 3-diphenyl-2-propenyl acetate with dimethyl malonate. Less
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