Dipolarophiles ethyl vinyl ketone

Facile reaction of electron-deficient olefins (dipolarophiles) such as rra/i5-dibenzoylethylene, dimethyl fumarate, furanonitrile, methyl vinyl ketone, ethyl crotonate, ethyl acrylate, ethyl methacrylate, and dimethyl maleate with a mesoionic compound containing a masked thiocarbonyl ylide skeleton gives stable 1 1 cycloadducts. The structure of the cycloadduct was established by its carbonyl absorption in IR spectra and the molecular ion peak [M]. The stereochemistry of the cycloadducts was, however, secured by NMR spectra (74JOC3631) (Scheme 100). 

Pyrido[l,2-c]quinazolin-8-ones (215) were obtained from the cycloadducts (214) of anhydro 3-hydroxythiazolo[3,2-c]quinazolin-4-ium hydroxides (213) and alkynic (dimethyl acetylenedicarboxylate and ethyl propio-late) and alkenic dipolarophiles (fumaronitrile and methyl vinyl ketone) by extrusion of S or H2S (85JOC1666). A better yield could sometimes be... 

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