Radical addition-polar termination cascade: efficient strategy for photoredox-neutral-catalysed cyclopropanation and Giese-type reactions of alkenyl N-methyliminodiacetyl boronates

Abstract

With radical addition-polar termination (RAPT) cascade as the strategy, efficient cyclopropanation and Giese-type reactions of alkenyl N-methyliminodiacetyl boronates have been realized by means of photoredox catalysis. With chloro- or bromomethyl silicate as the methylene source, a variety of cyclopropyl MIDA boronates as air- and chromatographically stable solids were prepared via photoredox-catalysed cyclopropanation of α-MIDA-boryl styrenes, 2-propenyl-BMIDA, and ethenyl-BMIDA. Moreover, photocatalytic Giese-type reactions of alkyl radicals with α-MIDA-boryl styrenes were also developed. It is essential for the successful radical conjugate addition employing alkyl silicates as the radical precursor. These RAPT cascades are characterized by a redox-neutral and additive-free process.