Date/Time
Date(s) - 26/11/2020
1:30 pm - 2:30 pm

Homologationof Aldehydes using Wittig Reagents as a Platform for Organocatalysis andMeroterpene Total Synthesis  

Date:    Thursday, November 26, 2020 

Time:    1:30 p.m.   

Zoom:                    contact sprucel@mcmaster for details 

Supervisor:          Dr. Jim McNulty 

Abstract:             

 Quaternary alkyl phosphonium salts were investigatedas four-carbon aldehyde homologating reagents to generate functionalizedolefins containing a latent methyl ketone moiety in the form of a cyclicacetal. The directing effect of the acetal on selective ylid formation wasinvestigated. Decreasing chelating power of the reaction solvent correlated toincreased chemoselectivity in ylid formation with lithium-containing bases,which suggested that lithium complexation by the acetal functionality may playa role in directing deprotonation.

Stabilized ylids derived from chloroacetone andtripropyl phosphonium salts were investigated as two-carbon homologatingreagents for the synthesis of methyl vinyl ketones (MVKs). A substrate scopewas established for a variety of aromatic and aliphatic aldehydes. The MVKsserved as a platform for organocatalytic Michael reactions, while aMichael-Claisen sequence provided entry to the synthesis of olivetol togetherwith methyl ether-, methyl ester- and ethanolamide-containing derivatives.Furthermore, a linear synthesis of cannabichromene methyl ester and cannabinolwas executed via the organocatalyzed condensation of citral andconcomitant 6?-electrocyclization.