Et3SiH + KO t Bu provide multiple reactive intermediates that compete in the reactions and rearrangements of benzylnitriles and indolenines.

Andrew J Smith,Jude N Arokianathar,Stuart G Leach,Darren L Poole,Kenneth F Clark,John A Murphy,Daniela Dimitrova

doi:10.1039/d0sc04244g

Abstract

The combination of potassium tert-butoxide and triethylsilane is unusual because it generates multiple different types of reactive intermediates simultaneously that provide access to (i) silyl radical reactions, (ii) hydrogen atom transfer reactions to closed shell molecules and to radicals, (iii) electron transfer reductions and (iv) hydride ion chemistry, giving scope for unprecedented outcomes. Until now, reactions with this reagent pair have generally been explained by reference to one of the intermediates, but we now highlight the interplay and competition between them.

Highlights

A novel reducing system, consisting of the reagent-pair, triethylsilane and potassium tert-butoxide was reported by Stoltz, Grubbs et al in 2013.1 The combination of the two reagents has since been investigated by a number of research groups[2,3,4,5,6,7,8,9,10,11,12,13,14,15] and provides a range of distinctive reaction types, arising through an unprecedented menu of reactive intermediates formed in the reaction, including triethylsilyl radicals 1, silanates 2 as hydrogen atom donors to both closed shell molecules and to radicals, and as potential hydride ion donors, and tert-butoxytriethylsilyl radical anions 3 as a very powerful electron donor
Exposing substrates simultaneously to multiple reactive intermediates is not routinely encountered in organic chemistry, other than in modelling of prebiotic conditions,[16] and so the variety of reactive intermediates produced by this reagent pair provides opportunities to witness unusual outcomes
Murphy et al have reported that N-benzylindoles 9 are deprotected by electron transfer reactions with 3 acting as electron donor.[7]

Summary

Introduction

A novel reducing system, consisting of the reagent-pair, triethylsilane and potassium tert-butoxide was reported by Stoltz, Grubbs et al in 2013.1 The combination of the two reagents has since been investigated by a number of research groups[2,3,4,5,6,7,8,9,10,11,12,13,14,15] and provides a range of distinctive reaction types, arising through an unprecedented menu of reactive intermediates formed in the reaction, including triethylsilyl radicals 1, silanates 2 as hydrogen atom donors to both closed shell molecules and to radicals, and as potential hydride ion donors, and tert-butoxytriethylsilyl radical anions 3 as a very powerful electron donor. Entry 2 shows that when the silane was replaced by the disilane 44 (Scheme 5) in the presence of the electron donor 47,24 the radical anion of di-p-tert-butylbiphenyl, the cyclisation reaction was still observed, affording 24 (19%).

Results

Conclusion