Pyridines, acylation

NQR, 2, 125 Pyridines, acetylalkyl-alkyl deacetylation, 2, 301 Pyridines, acetyltrimethyl-synthesis, 2, 470 Pyridines, acyl-conformation, 2, 162 reactions, 2, 337 Pyridines, alkenyl-ozonolysis, 2, 334 reactions, 2, 334 Pyridines, alkenyldihydro-disproportiation, 2, 62 Pyridines, alkyl-... 

Ellipticine quinones have an intrinsic interest as antitumor agents <04JME4958> and are also known intermediates in the synthesis of ellipticines <02CRV4303>. For instance, ellipticine quinones 53b and 53c have been transformed into the alkaloid ellipticine <80JA1457 90J(P1)1319 98H(48)1593>. Hence, these homolytic pyridine acylations by 2-indolylacyl radicals also constitute formal syntheses of the natural product. 

The HCo(CO)4-catalyzed hydrocarboxylation of alkenes has also been known for a long time. The mechanism is analogous to that presented for hydroformyla-tion (Scheme 1), except that H2O is used instead of H2. Hydrocarboxylation is generally slower than hydro-formylation, and it is believed that the concentrations of the intermediate species are quite low relative to those seen for hydroformylation. Pyridine has a rateenhancing effect that is believed to be due to the facile cleavage of the (acyl)Co(CO)4 intermediate. This reaction forms [pyridine-acyl] + [Co(CO)4] , which is more rapidly hydrolyzed by water to form the product carboxylic acid and HCo(CO)4. 

In order to understand the effect of these catalysts, it is important to observe that they do not act themselves as enhancers (no effect on light output is observed, when used alone). An explanation is proposed by considering in more detail the reaction steps from diazaquinone (L) to the luminol peroxide intermediate. This reaction involves nucleophilic attack on one of the diazaquinone carbonyls by hydrogen peroxide monoanion. A hydroperoxide species is formed, which can rearrange to the endoperoxide. Either compound is very unstable and collapses to 3-amino-phthalate in its excited state. Perhaps pyridine acylation catalysts could facilitate hydrogen peroxide attack by converting L into a more reactive intermediate. 

In the presence of pyridine, acyl chlorides react with alcohols to give esters according to the following overall equation ... 

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