Investigating the different mechanisms involved in a silane-alkoxide system

Student thesis: Doctoral Thesis

Abstract

Recent publications by Grubbs and Stoltz have focussed on the combination of triethylsilane with potassium tert-butoxide to afford a system which is capable of carrying out a number of synthetically useful transformations. This includes i) the reductive cleavage of C-O bonds in ethers, ii) the reductive cleavage of C-S bonds in thioethers, and iii) the regioselective silylation of arenes and heteroarenes. A number of mechanistic studies have been carried out, but so far no conclusive mechanism is known for these transformations.Recent work in the Murphy group has focussed on the combination of small molecules with potassium tert-butoxide to form in situ electron donors. This thesis will focus on mechanistic studies on the combination of triethylsilane with potassium tert-butoxide, which is capable of carrying out the reductive debenzylation of N-benzylindoles (Scheme 1). Experimental and computational studies show that it is likely that this transformation proceeds via single electron transfer.Scheme 1 - Debenzylation of N-Benzylindoles Mediated by Et3SiH/KOtBu [includes graphic]N-arylindoles were shown to undergo ring-opening and subsequent ring-closure to afford 9,10-dihydroacridines (Scheme 2). Mechanistic studies suggest that this transformation may either proceed via single electron transfer or via hydrogen atom transfer.Scheme 2 - Conversion of N-Arylindoles to 9,10-Dihydroacridines Mediated by Et3SiH/KOtBu [includes graphic]Finally, the reduction and subsequent cyclisation of nitriles was shown to proceed via hydride transfer from the Et3SiH/KOtBu system, with the displacement of the methoxide group occurring via a concerted nucleophilic aromatic substitution (i.e. without the formation of a Meisenheimer intermediate, Scheme 3).Scheme 3 - Concerted Nucleophilic Aromatic Substitution to Afford Indolines [includes graphic]
Date of Award5 Mar 2020
Original languageEnglish
Awarding Institution
  • University Of Strathclyde
SponsorsEPSRC (Engineering and Physical Sciences Research Council)
SupervisorJohn Murphy (Supervisor) & David Nelson (Supervisor)

Cite this