An unusual formal migrative cycloaddition of aurone-derived azadienes: synthesis of benzofuran-fused nitrogen heterocycles

Qiang Feng; An Wu; Xinhao Zhang; Lijuan Song; Jianwei Sun

doi:10.1039/d1sc00941a

An unusual formal migrative cycloaddition of aurone-derived azadienes: synthesis of benzofuran-fused nitrogen heterocycles

Chem Sci. 2021 May 4;12(22):7953-7957. doi: 10.1039/d1sc00941a.

Authors

Qiang Feng¹, An Wu¹, Xinhao Zhang², Lijuan Song³, Jianwei Sun^{1

4}

Affiliations

¹ Department of Chemistry, Shenzhen Research Institute, The Hong Kong University of Science and Technology Clear Water Bay Kowloon Hong Kong SAR China sunjw@ust.hk.
² Shenzhen Bay Laboratory, State Key Laboratory of Chemical Oncogenomics, Peking University Shenzhen Graduate School Shenzhen China.
³ School of Science, Harbin Institute of Technology (Shenzhen) Shenzhen 518055 China songlijuan@hit.edu.cn.
⁴ The Hong Kong Branch of Chinese National Engineering Research Centre for Tissue Restoration & Reconstruction Clear Water Bay Kowloon Hong Kong SAR China.

Abstract

Aurone-derived azadienes are well-known four-atom synthons for direct [4 + n] cycloadditions owing to their s-cis conformation as well as the thermodynamically favored aromatization nature of these processes. However, distinct from this common reactivity, herein we report an unusual formal migrative annulation with siloxy alkynes initiated by [2 + 2] cycloaddition. Unexpectedly, this process generates benzofuran-fused nitrogen heterocyclic products with formal substituent migration. This observation is rationalized by less common [2 + 2] cycloaddition followed by 4π and 6π electrocyclic events. DFT calculations provided support to the proposed mechanism.