Facile isomerization of silyl enol ethers catalyzed by triflic imide and its application to one-pot isomerization–(2 + 2) cycloaddition

Kazato Inanaga,Yu Ogawa,Akihiro Daigaku,Kiyosei Takasu,Yoshiji Takemoto,Hidetoshi Tokuyama,Yuuki Nagamoto

doi:10.3762/bjoc.8.73

Abstract

A triflic imide (Tf2NH) catalyzed isomerization of kinetically favourable silyl enol ethers into thermodynamically stable ones was developed. We also demonstrated a one-pot catalytic reaction consisting of (2 + 2) cycloaddition and isomerization. In the reaction sequence, Tf2NH catalyzes both of the reactions.

Highlights

Silyl enol ethers, which are isolable equivalents of metal enolates, are useful and important intermediates in synthetic chemistry [1,2,3]
During our research on triflic imide (Tf2NH)-catalyzed reactions [8], we accidentally found that the isomerization of kinetically favourable silyl enol ethers into thermodynamically stable ones occurs smoothly in the presence of Tf2NH
The catalytic isomerization reaction proceeded in toluene, but no isomerization occurred in CH3CN

Summary

Introduction

Silyl enol ethers, which are isolable equivalents of metal enolates, are useful and important intermediates in synthetic chemistry [1,2,3]. During our research on triflic imide (Tf2NH)-catalyzed reactions [8], we accidentally found that the isomerization of kinetically favourable silyl enol ethers into thermodynamically stable ones occurs smoothly in the presence of Tf2NH. When the TBS enol ether 1a was treated with a catalytic amount of Tf2NH (1.0 mol %) in CH2Cl2 at ambient temperature, isomerization resulted in the thermodynamically stable 2a in 92% yield along with the recovered 1a and ketone 3 (Table 1, entry 1). The reaction using 20 mol % of Tf2NH resulted in an increase of decomposition into 3 (entry 2).

Results

Conclusion