Chemistry Weekly Seminar - PhD Candidate Vankata Garapati

Title:

Synthesis and Study of Oxazolium Salts as Organocatalysts

Abstract:

N-Heterocyclic carbene (NHC) catalysis is an emerging field in organic synthesis. Imidazolium, thiazolium, and triazolium salts are typically employed as NHC pre-catalysts, which can catalyze the benzoin, Stetter, cross-benzoin, aza-benzoin, extended enolates, and acyl anion reactions. Oxazolium salts are another type of NHCs; however, these were unable to catalyze the homo-benzoin reaction of benzaldehyde due to their sensitive nature towards basic alcoholic solution and oxygen. To overcome these issues, we prepared various N-substituted oxazolium salts and tested them in anhydrous aprotic solvents and oxygen-free reaction conditions. These are efficient catalysts, sometimes even better than traditional azolium salts. For instance, an N-mesityl oxazolium salt catalyzes the Stetter reaction of β-alkyl-α,b-unsaturated ketones and electron rich aldehydes with good yields. Moreover, known chiral thiazolium salts suffered from low yields, and enantioselectivities in NHC catalyzed transformations. Hence, to address these problems, we prepared more sterically hindered chiral thiazolium and oxazolium salts and explored them with promising results in the Stetter reaction.

Date:            Tuesday, April 23, 2019

Time:            10:30 a.m.

Location:    Thorvaldson 159