Chloral, Diels-Alder reaction

The carbonyl ene reaction is between a similarly reactive aldehyde and an alkene rather than aketene. Glyoxalate esters and chloral are typical of the carbonyl compounds involved. Asymmetric versions rely on Lewis acid catalysts similar to those used in Diels-Alder reactions based on Ti and A1 among other metals.43 A simple example is the formation of 190 from methyl glyoxalate and an alkene 189 catalysed by 0.5mol% of a BINOL-Ti complex 191. Other alkenes that react well are 192 -195. 

It has been recognized for many years that chloral will react with simple 1,3-dienes to afford reasonable yields of [4 + 2] adducts.6 7 The stereochemistry of the Diels-Alder reaction of cyclohexadiene and chloral7 has been reinvestigated and was unambiguously established to give the endo adduct [Eq. (2)].8... 

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