NMR Studies on 1,3-Dipolar Cycloaddition of Nitrile Oxides to Norbornenes

Mirosław Gucma,W Marek Gołębiewski,Maria Krawczyk

doi:10.5935/0103-5053.20130106

Abstract

The 1,3-dipolar cycloaddition reaction of nitrile oxides to norbornenes substituted with an acrylate-derived moiety was examined. Only adducts to norbornene system were formed with a good exo selectivity and complete site-selectivity. Structures of the products were elucidated by an extensive application of electrospray ionization-mass spectrometry (ESI-MS) and 2D 1H and 13C nuclear magnetic resonance (NMR).

Highlights

The 1,3-dipolar cycloaddition of nitrile oxides to alkenes is the most convenient method for the preparation of 2-isoxazolines[1] which can be reduced to several synthetically important compounds such as b-hydroxy ketones, b-hydroxy esters, a,b-unsaturated carbonyl compounds or iminoketones.[2]
Reaction of nitrile oxides with norbornadienes substituted with electron deficient groups in 2,3-positions afforded only adducts to the more electron-rich unsubstituted double bond.[5]
The 1,3-dipolar cycloaddition of 4-(trifluoromethyl) benzonitrile oxide (6) to norbornenes substituted with the acrylate group 3, 4 and an unsaturated urea derivative 5 was examined

Summary

Introduction

The 1,3-dipolar cycloaddition of nitrile oxides to alkenes is the most convenient method for the preparation of 2-isoxazolines[1] which can be reduced to several synthetically important compounds such as b-hydroxy ketones, b-hydroxy esters, a,b-unsaturated carbonyl compounds or iminoketones.[2]. Reaction of nitrile oxides with norbornadienes substituted with electron deficient groups in 2,3-positions afforded only adducts to the more electron-rich unsubstituted double bond.[5] On the other hand, 1,3-dipolar cycloaddition to norbornenes follows In reactions of nitrile oxides with dimethyl 7-(diphenylmethylene)bicyclo[2.2.1]hept-2-ene5,6‐dicarboxylate, only disubstitured norbornene double bond partcipated affording exclusively exo cycloadducts.[8]

Results

Conclusion