Use of Aryl Chlorides as Electrophiles in Pd-Catalyzed Alkene Difunctionalization Reactions
作者:Brandon R. Rosen、Joshua E. Ney、John P. Wolfe
DOI:10.1021/jo100344k
日期:2010.4.16
The development of conditions that allow use of inexpensive aryl chlorides as electrophiles in Pd-catalyzedalkenecarboamination and carboetherification reactions is described. A catalyst composed of Pd(OAc)2 and S-Phos minimizes N-arylation of the substrate and prevents formation of mixtures of regioisomeric products. A number of heterocycles, including pyrrolidines, isoxazolidines, tetrahydrofurans
Iminium ions generated from isoxazolidines and tetrahydro-1,2-oxazines undergo allylation under Sakurai conditions. Allylated isoxazolidines are formed predominantly as the trans isomer, while oxazines are formed exclusively as the cis isomer.
Synthesis of N,O-Heterocycles by Intramolecular Conjugate Addition of a Hydroxylamine
作者:Roderick Bates、Robert Snell、SusAnn Winbush
DOI:10.1055/s-2008-1072650
日期:——
Isoxazolidines and tetrahydro-1,2-oxazines were produced by a tandem deprotection-intramolecular Michael addition of hydroxylamines. For tetrahydrooxazine formation, high stereoselectivity was observed, even when a quaternary centre was formed.
Influence of Hydroxylamine Conformation on Stereocontrol in Pd-Catalyzed Isoxazolidine-Forming Reactions
作者:Georgia S. Lemen、Natalie C. Giampietro、Michael B. Hay、John P. Wolfe
DOI:10.1021/jo8027399
日期:2009.3.20
Palladium-catalyzed carboamination reactions between N-Boc-O-(but-3-enyl)hydroxylamine derivatives and aryl or alkenyl bromides afford cis-3,5- and trans-4,5-disubstituted isoxazolidines in good yield with up to >20:1 dr. The diastercoselectivity observed in the formation of cis-3,5-disubstituted isoxazolidines is superior to selectivities typically obtained in other transformations, such as 1,3-dipolar cycloaddition reactions, that provide these products. In addition, the stereocontrol in the C-N bond-forming Pd-catalyzed carboamination reactions of N-Boc-O-(but-3-enyl)hydroxylamines is significantly higher than that of related C-O bond-forming carboetherification reactions of N-benzyl-N-(but-3-enyl)hydroxylamine derivatives. This is likely due to a stereoelectronic preference for cyclization via transition states in which the Boc group is placed in a perpendicular orientation relative to the plane of the developing ring, which derives from the conformational equilibria of substituted hydroxylamines.
Palladium-Catalyzed Ring-Forming Alkene Aminoaroylation of Unsaturated Hydrazones and Sulfonamides
The first example of a Pd(OAc)(2)-catalyzed ring-forming alkene aminoaroylation of unsaturated hydrazones and sulfonamides is described. This protocol features the use of diaryliodonium salts as both oxidants and aryl sources, thus enabling mild reaction conditions, good chemoselectivity, a broad substrate scope, and high functional group tolerance. A wide range of synthetically and biologically important functionalized dihydropyrazoles and isoxazolidines have been obtained in good yields.