Maleic acid with 1,4-dihydropyridines

In general only very electron-deficient double bonds will react spontaneously with 1,4-dihydropyr-idines. (This statement applies to nonenzymic chemistry enzymatically, as in LAD, NAD(P)H, with a lesser reduction potential than many of the 1,4-dihydropyridines used in abiotic reactions, reduces unactivated carbonyl groups.) Thiobenzophenone, quinone, maleic acid, and hexachloroacetone react spontaneously with simple dihydropyridines and undergo reduction (the carbon-carbon double bond of maleic anhydride is reduced). Trifluoroacetophenone will also often react spontaneously with 1,4-dihydro-pyridines. 

Much more work has involved N-protected 1,2-dihydropyridines thus, DielsAlder reactions between dihydropyridine 533 and many acrylic acid esters or dimethyl maleate have been described, though variable yields of endo 543 and exo 544 2-azabicyclo[2.2.2]octene products are obtained. The reaction with maleic anhydride yielded only the endo product 545 <2003T7555>. Chiral catalysts have been developed to allow the enantioselective DielsAlder reactions of 1,2-dihydropyridines <2002T8299>. 

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