Quinones 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. 

The treatment of glutarimide (586) with two equivalents of r-butyldimethylsilyl triflate (587) in the presence of Et3N gives rise to 2,6-bis(t-butyldimethylsiloxy)-3,4-dihydropyridine (588) (equation 297)330. Quinone (589) and hexamethyldisilazane (405) in the presence of iodine as catalyst form l,4-bis(TMS)-hydroquinone (590) (equation 298)331. 

The synthesis is easier than expected as heating together a mixture of acetoacetate ester, formaldehyde, and ammonium acetate gives dihydropyridine (57). Oxidation with a quinone such as DDQ (Chapter 36) gives the pyridine. 

The reaction of l-Boc-2-lithio-l,4-dihydropyridines with 3,4-disubstituted cyclobutadienes provides the quinoline quinone upon heating and treatment with acetic acid... 

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