Investigating the different mechanisms involved in a silane-alkoxide system

  • Andrew Smith

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)

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