LiGaH4, in combination with the S,O-chelate 2-hydroxy-2'-mercapto-1,1'-binaphthyl (MTBH2), forms an active catalyst for the asymmetric reduction of prochiral ketones, with catecholborane as the hydride source. Enantioface differentiation is on the basis of the steric requirements of the ketone substituents. Aryl/ n-alkyl ketones are reduced in 90-93% ee and RC(O)Me (e.g. R = iPr, cycloC6H11, tBu) in 60-72% ee. Other borane sources and alternative catalyst structures based on indium do not form enantioselective catalysts.
In the presence of enantiopure MTBH(2)(monothiobinaphthol, 2-hydroxy-2[prime or minute]mercapto-1,1[prime or minute]-binaphthyl; 0.2 eq.) quantitative allylation of ArC([double bond]O)Me takes place with impure Sn(CH(2)CH[double bond]CH(2))(4)(prepared from allyl chloride, air-oxidised magnesium and SnCl(4)) to yield tert-homoallylic alcohols in 85-92% ee. In the same process highly purified, or commercial, Sn(CH(2)CH[double bond]CH(2))(4) yields material of only 35-50% ee. The origin of these effects is the presence of small amounts of the compounds, EtSn(CH(2)CH[double bond]CH(2))(3), ClSn(CH(2)CH[double bond]CH(2))(3) ClSnEt(CH(2)CH[double bond]CH(2))(2) in the tetraallyltin sample and the presence of traces of water (which inhibits achiral background reactions). All the triallyl and diallyl species enhance the stereoselectivity in the catalytic allylation reaction, the chlorides more so than the ethyl compound. Hydrolysis of ClSnEt(CH(2)CH[double bond]CH(2))(2) affords crystallographically characterised Sn(4)(mu(3)-O)(mu(2)-Cl)(2)Cl(2)Et(4)(CH(2)CH[double bond]CH(2))(4). Reaction of this latter compound with MTBH(2) leads to the most potent catalyst.
In the presence of the monothiobinaphthol (MTB) ligand aryl ketones are allylated by mixtures of Sn(CH 2 CH=CH 2 ) 4 / RSn(CH 2 CH=CH 2 ) 3 (R = Et, Bu) in high e.e. The presence of water suppresses racemic background allylation.
Reaction of (R a ) or (S a )-2-(N,N-dialkylcarbamoyloxy)-2Ј-hydroxy-1,1Ј-binaphthyls (diethyl and diisopropyl derivatives) with α,ω-I(CH 2 ) n I (n = 6, 8) in the presence of K 2 CO 3 leads to the formation 1,n-bis{2Ј-[2-(N,Ndialkylcarbamoyloxy)-1,1Ј-binaphthyl]oxy}alkanes. These diethers when treated with Bu s Li-TMEDA fashion 1,n-bis{2Ј-[2-hydroxy-3-(N,N-dialkylamido)-1,1Ј-binaphthyl]oxy}alkanes, the products of double anionic Fries rearrangement.
New C2-Chiral Bidentate Ligands Bridging the Gap Between Donor Phosphine and Acceptor Carbonyl Ligands. -Starting from the enantiomerically pure cyclopentanediol (+)-(I) the new C2 chiral bidentate phosphorus ligands (III) and (V) are prepared. Their enantiomers are analogously obtained from (-)-(I). Photolysis of η6-benzene-tricarbonyl-chromium in the presence of the two new ligands affords the complexes (VI) which show the new ligands to be intermediates in their bonding properties between alkyl phosphites and CO. -(KUENDIG, E. P.; DUPRE, C.; BOURDIN, B.; CUNNINGHAM, A. JUN.; PONS, D.; Helv. Chim. Acta 77 (1994) 3, 421-428; Dep. Org. Chem., Univ. Geneva, CH-1211 Geneva 4, Switz.; EN)
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