GWC2 Wednesday Afternoon Research Seminars: Adrian Schwan

Adrian Schwan
Department of Chemistry
University of Guelph

Wednesday, November 13, 2019
2:30 p.m.
Main Link Room (EIT-2053/MacN-101)

Coffee and treats will be served.
All are welcome to attend this weekly seminar series.

Abstract:
Sulfenic acid anions (RSO^-M⁺)¹ represent a means of introducing nucleophilic sulfur entities already possessing a single oxygen. These species are prochiral and their alkylation chemistry results in the direct formation of a sulfoxide while providing possibilities for stereoselectivity, since the sulfoxide is a stereogenic centre. The Schwan group has demonstrated a number of diastereoselective alkylation reactions and has suggested various internal coordination structures involving the sulfenate counterion to account for the observed stereoselectivity.^2,3

We have achieved diastereoselective alkylation chemistry, using both sulfenates and electrophiles which hold internal carbon chirality. In one case, the products have been further elaborated to provide a preparation of isomeric dialkyl pyrrolidines, known constituents of ant venom.⁴

We have also established that benzylation of a protected cysteinesulfenate occurs with dr’s ranging from 89:11 to 95:5.² Recently, we have initiated model computational studies to assist in determining the origins of the diastereoselection. Our findings identify the relative importance of lithium counterion coordination and sulfenate oxygen hydrogen bonding.⁵ We have also modelled substrates that possess an asymmetric b-(protected)amino group with varied protection groups.

The talk will outline some fundamentals of sulfenate chemistry, our contributions to diastereoselective alkylations, the preparation of the pyrrolidine alkaloids and the computational work which identifies sulfenate structures that may be responsible for the stereochemical outcomes.

1. O’Donnell, J. S.; Schwan, A. L. J. Sulfur Chem. 2004, 25, 183− 21
2. Schwan, A. L.; Verdu, M. J.; Singh, S. P.; O’Donnell, J. S.; Ahmadi, A. N. J. Org. Chem. 2009, 74, 6851−6854.
3. Soderman, S.C.; Schwan, A.L. J. Org. Chem. 2013, 78, 1638−1649.
4. Soderman, S.C.; Schwan, A.L. Org. Lett.  2013, 15, 4434–4437
5. Schwan, A.L.  Eur. J. Org. Chem. 2019, 519–526.

Upcoming (GWC)² Wednesday Afternoon Research Seminars – Fall 2019