Functionalized spirolactones by photoinduced dearomatization of biaryl compounds.

Hongji Li,Anon Bunrit,Joseph S M Samec,Feng Wang,Elena Subbotina

doi:10.1039/c8sc05476b

Abstract

The idea of using biaryl structures to generate synthetic building blocks such as spirolactones is attractive because biaryl structures are abundant in biomass waste streams. However, the inertness of aromatic rings of biaryls makes it challenging to transform them into functionalized structures. In this work, we developed photoinduced dearomatization of nonphenolic biaryl compounds to generate spirolactones. We demonstrate that dearomatization can be performed via either aerobic photocatalysis or anaerobic photooxidation to tolerate specific synthetic conditions. In both pathways, dearomatization is induced by electrophilic attack of the carboxyl radical. The resulting spirodiene radical is captured by either oxygen or water in aerobic and anaerobic systems, respectively, to generate the spirodienone. These methods represent novel routes to synthesize spirolactones from the biaryl motif.

Highlights

Biaryl compounds are abundant in biomass waste streams from pulping of lignocellulose.[1,2,3,4] In the lignin structure, the biphenyl linkage is known as the 5–50 bond which is inert and preserved during the pulping of biomass (Fig. 1)
The idea of using biaryl structures to generate synthetic building blocks such as spirolactones is attractive because biaryl structures are abundant in biomass waste streams
The resulting spirodiene radical is captured by either oxygen or water in aerobic and anaerobic systems, respectively, to generate the spirodienone

Summary

Introduction

Biaryl compounds are abundant in biomass waste streams from pulping of lignocellulose.[1,2,3,4] In the lignin structure, the biphenyl linkage is known as the 5–50 bond which is inert and preserved during the pulping of biomass (Fig. 1). To investigate the feasibility of our two methods and reveal the differences between the aerobic and anaerobic systems, a range of different 1,10-biaryl-2-carboxylic acids were tested using the two reaction conditions (Fig. 2).

Results

Conclusion