Influence of Hydroxylamine Conformation on Stereocontrol in Pd-Catalyzed Isoxazolidine-Forming Reactions
摘要:
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.
Microwave-induced organometallic reactions in aqueous media. Use of Ga and Bi for the allylation of aromatic N-oxides and hydrazones
作者:Dhrubojyoti D. Laskar、Mukut Gohain、Dipak Prajapati、Jagir S. Sandhu
DOI:10.1039/b108525p
日期:2002.2.11
Homoallylic hydroxylamines and homoallylic hydrazides were synthesised in excellent yields by the reaction of allylgallium or allylbismuth reagent, generated in situ in the presence of 0.1 equivalent of NH4Cl–Bu4NBr, with aldonitrones and hydrazones in aqueous media. The reaction rate can be increased dramatically under microwave activation.
Organometallic reaction in aqueous media. A samarium induced, efficient, synthesis of homoallyl hydroxylamines and hydrazides
作者:Dhrubojyoti D Laskar、Dipak Prajapati、Jagir S Sandhu
DOI:10.1016/s0040-4039(01)01637-9
日期:2001.10
Samarium can be used directly for the allylation of aldonitrones and hydrazones in aqueous media in the presence of Bu4NBr. (C) 2001 Elsevier Science Ltd. All rights reserved.
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.
Hydroxylamine Oxygen as Nucleophile in Palladium(0)- and Palladium(II)-Catalyzed Allylic Alkylation: A Novel Access to Isoxazolidines
In search for novel heterocyclization processes, the intramolecular Pd-mediated allylic alkylation of homoallyl hydroxyl-amines is described. Depending on both the reaction conditions and the substrates, CIS- or TRANS-3-substituted-5-vinyl isoxazolidines are preferentially obtained. The corresponding starting materials for the cyclization step are readily obtained through cross-metathesis of the easily