Manganese-Catalyzed 5-<i>Endo</i>-trig Oxygenative Cyclization of α,β-Unsaturated Oximes under Air and Ambient Conditions for the Synthesis of 4,5-Dihydroisoxazoles
The stereoselective 5-endo-trig oxygenativecyclization of α,β-unsaturatedoximes was achieved using molecular oxygen (O2) and a manganese catalyst. Several 4-hydroxy-4,5-dihydroisoxazoles were obtained in high yields by directly incorporating O2 from the atmosphere (eliminating the necessity for a pure oxygen environment) and using an unprecedentedly low loading of Mn(acac)3 (as little as 0.020 mol
Cooperativity of Regiochemistry Control Strategies in Reductive Couplings of Propargyl Alcohols and Aldehydes
作者:Hasnain A. Malik、Mani Raj Chaulagain、John Montgomery
DOI:10.1021/ol902561r
日期:2009.12.17
The nickel-catalyzed reductive coupling of propargyl alcohols and alkynes proceeds with excellent regiochemical control with an underlying electronic preference that can be supplemented by ligand size effects. The products obtained may be readily converted to substructures that are not directly available by an aldehyde-alkyne reductive coupling. A simple model for how steric and electronic factors are both important in governing regiochemistry in couplings of this type is presented, along with examples of how the effects can combine in either a constructive or destructive manner.
Stereochemical aspects of the asymmetric synthesis of chiral α,β-dihydroxy phosphonates. Synthesis of α,β-dihydroxy phosphonic acids
The nature of the O-protecting group is crucial to obtain, in terms of diastereoselectivity and chemical yields, the best results. An abinitiomolecularorbitalstudy on 2-silyloxy propanal and MM2 studies on 2-alkoxy propanal show the existence of stable cyclic and acyclic conformers, which are presumably responsible for the high syn diastereoselectivity observed in the addition of non-metal carrying