Catalytic asymmetric synthesis of protected α-hydroxy aldehydes and related 1,2-difunctional chiral building blocks. An enantioselective synthesis of (−)-exo- and (−)-endo-brevicomin
摘要:
Chiral allylic alcohols which were prepared by the addition of functionalized dialkylzincs to alpha,beta-unsaturated aldehydes in good to excellent enantioselectivity, were converted to protected alpha-hydroxy aldehydes and 1,2-amino alcohols without loss of enantiomeric purity. Syn- or anti-1,2-diols can be obtained stereoselectively by a second asymmetric addition to alpha-silyloxy aldehydes. Functionalized 1,2-diols prepared in this way were converted to enantiomerically pure (-)-exo- and (-)-endo-brevicomin (>99% ee). (C) 1997 Elsevier Science Ltd.
A new strategy has been established for the kineticresolution of racemic allylic alcohols through a palladium/sulfonyl‐hydrazide‐catalyzed asymmetric OH‐substitution under mild conditions. In the presence of 1 mol % [Pd(allyl)Cl]2, 4 mol % (S)‐SegPhos, and 10 mol % 2,5‐dichlorobenzenesulfonyl hydrazide, a range of racemic allylic alcohols were smoothly resolved with selectivity factors of more than
Nickel-Catalyzed Preparations of Functionalized Organozincs
作者:Stephan Vettel、Andrea Vaupel、Paul Knochel
DOI:10.1021/jo960808v
日期:1996.1.1
(X = Br, Cl) via a halogen-zinc exchange reaction. The treatment of terminal alkenes with diethylzinc (neat, 25-60 degrees C) in the presence of Ni(acac)(2) as a catalyst (1-5 mol %) and 1,5-cyclooctadiene (COD) affords the corresponding dialkylzincs via a hydrozincation reaction. Whereas the conversion for simple alkenes bearing a remote functionality reaches 40 to 63%, the hydrozincation of allylic
A new preparation of diorganozincs from olefins via a nickel catalyzed hydrozincation
作者:Stephan Vettel、Andrea Vaupel、Paul Knochel
DOI:10.1016/0040-4039(94)02438-h
日期:1995.2
The reaction of olefins with diethylzinc in the presence of catalytic amounts of Ni(acac)2 provides dialkylzincs (neat, 40–50 °C, 2–6 h). These zinc reagents can be trapped by various electrophiles or used for the catalyticasymmetricaddition to aldehydes (> 85 % ee). Allylic and homoallylic alcohols are especially good substrates for the reaction.