Regioselective Hydrolysis of Alkynes Via Organosulfur Intermediates

Abstract

Many known synthetic methods enable the hydrolysis of alkynes with Markovnikov regioselectivity. In contrast, the synthetic chemist’s toolbox lacks broadly effective processes for the hydrolysis of alkynes with anti-Markovnikov regioselectivity. This thesis describes the development of new synthetic method that will help address this deficiency. This document begins with a review of the concepts of Markovnikov and anti-Markovnikov regioselectivity and an explanation of the broad extension of this terminology that is applied throughout the remainder of this thesis to encompass all alkyne substrates. Next, a review of the published methods of alkyne hydrolysis is presented, with emphasis on the internal alkyne substrates. The remainder, and bulk, of this thesis details the development of a new synthetic methodology that leverages regioselective radical thiolation chemistry to achieve anti-Markovnikov hydrolysis of alkynes. Internal alkynes are first converted to oxathiolanes or vinyl sulfides with anti-Markovnikov regioselectivity followed by hydrolysis of these moieties to the corresponding anti-Markovnikov ketones. In the case of aryl-alkyl alkyne substrates, complete anti-Markovnikov selectivity is demonstrated with a broad range of examples. Aryl-aryl alkyne substrates offer a mixture of regioisomers favoring anti-Markovnikov products. Finally, the utility of this methodology is demonstrated with its application to the successful first total synthesis of the bioactive natural product isomeranzin.