Functionalized esters hydroxyesters

A very useful method for generating 3 (2H)- dihydrofuranones is based on the Michael addition of anions derived from a-hydroxyesters to a,/3-unsaturated substrates (Scheme 82). The intermediate anion attacks the adjacent ester moiety via a Dieckmann condensation reaction to produce a substituted furanone ring which usually bears useful functionality. Overall yields of 45-60% have been obtained for this reaction. 

Vindoline belongs to the vinca alkaloids, an important class of indole alkaloids whose dimers (such as vincadifformine) are anti-cancer compounds. The most difficult functionality in this compound is the tertiary a-hydroxyester and Langlois37 proposed to make this by hydroxylation of the related keto-ester 238. 

The explosion in novel reactions catalyzed by NHCs began with the 2004 disclosure of the first internal redox reactions of a-functionalized aldehydes by NHCs. The Bode group reported the thiazolium-catalyzed conversion of a,p-epoxyaldehydes to p-hydroxyesters (Scheme 14.5). This reaction produced esters without the need for stoichiometric coupling reagents, and... 

---