| 19555058 |
Weir ML, Cade IA, Kilah NL, Zhou X, Wild SB: Asymmetric synthesis of bis (tertiary arsines): highly stereoselective alkylations of diastereomers of a chiral phosphine-stabilized bis (arsenium triflate). Inorg Chem. 2009 Aug 3;48(15):7482-90.
The addition of organolithium reagents to an equilibrating mixture of diastereomers of a phosphine-stabilized 1,2-ethanediylbis (phenylarsenium triflate) containing chiral arsenic stereocenters and an enantiomerically pure, atropisomeric tertiary phosphepine derived from lithiated (aR)-2,2'-dimethyl-1,1'-binaphthalene generates unequal mixtures of diastereomers and enantiomers of chelating 1,2-ethanediylbis (tertiary arsines), chiral at arsenic, with liberation of the (aR (P))-phosphepine. Thus, the addition of methyllithium in diethyl ether at -95 degrees C to a dichloromethane solution of the complex (R*(As),R*(As))-(+/-)/(R*(As),S*(As))-1,2-[(R (3) P) PhAsCH (2) CH (2) AsPh (PR (3) )](OTf)(2), where R (3) P is (aR (P))-[2-(methoxymethyl) phenyl] phosphepine, generates (R*(As),R*(As))-(+/-)-1,2-ethanediylbis (methylphenylarsine) in 78% diastereoselectivity and 95% enantioselectivity in favor of the (R (As),R (As)) enantiomer. Under similar conditions, the addition of n-butyllithium in hexanes to a solution of the bis (phosphepine-stabilized)-diarsenium triflate at -95 degrees C gives the corresponding (R*(As),R*(As))-(+/-)-1,2-ethanediylbis [(n-butyl) phenylarsine) in 77% diastereoselectivity and 93% enantioselectivity in favor of the (R (As),R (As)) enantiomer. |
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