Arylboronic acid-catalysed dehydrative substitution of alcohols

Abstract

This thesis is focused on the investigation of new procedures for the activation of alcohols towards dehydrative nucleophilic substitution reaction that release water as the sole by- product using commercially available arylboronic acids as catalysts.

First, in Chapter I, the concept and background of dehydrative nucleophilic substitution reactions using Lewis or Brønsted acid catalysis is detailed. The use of boron-based catalyst for the activation of alcohols towards different reactions is described, with the intention of placing the work of this thesis in the context of the literature.

In Chapter II, the development of a new system for the catalytic activation of benzylic alcohols towards dehydrative substitution using a second alcohol as the nucleophile is described. A commercially available arylboronic acid catalyst in combination with oxalic acid as a ligand can be used for the synthesis of symmetrical, cyclic, and unsymmetrical ethers. Mechanistic control experiments have identified a possible active catalytic species in the reaction media and a plausible reaction mechanism is discussed.

Chapter III focuses on the application of the newly developed catalyst system for the dehydrative substitution of benzylic alcohols using carbon-based nucleophiles. The procedure has been demonstrated for a range of C-C bond forming reactions using either 1,3-diketone derivatives or allyltrimethylsilane as the nucleophile.

Finally, in Chapter IV, a new protocol for the dehydrative Nazarov electrocyclization of allylic alcohols to form substituted furans is investigated. The optimised procedure uses a readily available arylboronic acid catalyst under mild conditions to promote the dehydrative cyclisation. Preliminary control experiments detailing the preparation of the possible active catalytic species are also described.