Highly regioselective nitrile oxide dipolar cycloadditions with ortho-nitrophenyl alkynes
作者:Melissa L. McIntosh、Michael R. Naffziger、Bradley O. Ashburn、Lev N. Zakharov、Rich G. Carter
DOI:10.1039/c2ob26267c
日期:——
The dipolar cycloadditions of ortho-nitrophenyl alkynes with aryl nitrileoxides has been demonstrated. A range of substituents are tolerated on the alkyne. These reactions proceed with excellent levels of regioselectivity. Subsequent functionalization of the isoxazole scaffold has been demonstrated.
Conventional methods generate nitrile oxides from oxime halides in organic solvents under basic conditions. However, the present work revealed that water‐assisted generation of nitrile oxides proceeds under mild acidic conditions (pH 4–5). Cycloadditions of nitrile oxides with alkynes and alkenes easily occurred in water without using catalysts, thus yielding isoxazoles and isoxazolines, respectively
Nitrile oxides are oxidized by tertiary amine N-oxides in different solvents at room temperature to afford in the presence of dienes nitrosocarbonyl adducts in fair yields. The mild conditions used in oxidizing a variety of nitrile oxides promise a wide application of this method in synthetic processes.
Enolate-mediated 1,3-dipolar cycloaddition reaction of β-functionalized ketones with nitrile oxides: direct access to 3,4,5-trisubstituted isoxazoles
作者:Xiao Zhou、Xianhong Xu、Zhenyan Shi、Kun Liu、Hua Gao、Wenjun Li
DOI:10.1039/c6ob00717a
日期:——
TMG-catalyzed [3 + 2] organocatalytic 1,3-dipolarcycloaddition reactions of β-functionalized ketones with nitrileoxides have been developed. This strategy could generate 3,4,5-trisubstituted isoxazoles in high yields and regioselectivities.