Pyridine derivatives reaction with, phosgene

Enantiomers of carboxylic acids may sometimes be separated by GC as methyl esters, but special derivatives are mostly prepared for this purpose. Ackman et al. [188] resolved enantiomers of isoprenoid fatty acids after their conversion into L-menthyl esters. The acids under analysis were chlorinated by refluxing with distilled freshly prepared thionyl chloride and the chlorides produced were treated with L-menthol in the presence of pyridine under strictly anhydrous conditions. GC separation was carried out in a capillary column coated with butanediol succinate polyester. Annett and Stumpf [189] made use of L-menthyloxycarbonyl derivatives for the separation of enantiomers of methyl esters of hydroxy acids. The derivatization reagent, L-menthyl chloroformate, was prepared by the reaction of L-menthol with phosgene, with cooling with ice. Diastereoisomers of different hydroxy acids were thus separated on 1.5% OV-210. 

In contrast, the reaction of pyridine Al-oxide, or its 3-methyl or 4-methyl derivative) with phosgene in dichloromethane, in the absence of added base, gives hydrolytically unstable carbonate salts [811aa] ... 

The anhydrides 186 react with primary amines in alcohol and form compounds 187. The reaction of the latter with phosgene in pyridine (80°C) [104], in boiling benzene [109, 110], or in toluene (90°C) [111] leads to cyclization with the formation of 2,4-quinazolinedione derivatives 188 [104, 109-111],... 

N-(Phenoxycarbonyloxy)thiopyridone derivatives 99 are efficient iinimolecular photochemical sources for the clean generation of phenoxyl radicals. They are prepared by the reaction of lithium phenoxides with phosgene (from triphosgene and pyridine in a 1 3 molar ratio) [56]. 

Polycarbonates are polyesters of carbonic acid formed by reaction of diols (aromatic, aliphatic or a mixture of both) with a derivative of carbonic acid. The first preparations of polycarbonates were reported by Einhorn in 1898 [155], by reaction of phosgene with resorcinol or hydroquinone in a pyridine solution. Bischoff and van Hedenstrom in 1902 [156] obtained the same aromatic polycarbonates via transesterification with diphenyl carbonate (DPC). Thus the main routes to polycarbonates were established early, but the properties of the products seemed uninteresting. Around 1930 aliphatic polycarbonates were studied by Carothers and van Natta [157]. These carbonates have low melting points and thermal resistance and are not commercially interesting as stand-alone thermoplastics. Low molecular... 

More recently, the use of the chloroformate-aqueous alkali method has been revived by G. R. Barker and his associates in order to prepare a suitably protected D-ribose carbonate for a synthesis of a-D-ribofuranosyl phosphate. (An analogous synthesis of the latter compoimd, involving a phosgene-pyridine reaction, appeared almost simultaneously. ) Condensation of D-ribose with methyl chloroformate in the presence of aqueous sodium hydroxide led to the formation of a mixture of the anomers of l,5-di-0-(methoxycarbonyl)-D-ribofuranose 2,3-carbonate (LII), which was resolved by fractional recrystallization. The treatment of either of the derived D-ribofuranosyl chlorides with methanol and silver carbonate... 

Perhydro-oxazolo[3,4- ]pyridines have long been prepared by condensation between the appropriate piperidyl-2-carbinol and an aldehyde or ketone. For example, the antidepressant spiropiperidine derivative (135) is obtained by the reaction between a-phenyl-2-piperidine methanol and N-benzyl-4-piperidone (81USP4260623). Perhydro-oxazolo[3,4-a]pyridin-3-one (136) is obtained by phosgenation of 2-(hydroxymethyl)piperidinium p-toluene sulfonate followed by cyclization of the resultant chloroformate salt by treatment with triethylamine in dichloromethane. This ring system... 

Phosgene is reported to combine with a wide range of oxygenated materials, including alcohols, ethers, ketones, carboxylic acids, anhydrides, lactones, esters, carbonic acid derivatives, etc. Only the reactions of COCIF with alcohols, phenols and cyclic ethers have been reported, resulting usually in the generation of fluoroformates. Such materials can often be usefully converted into the corresponding fluoro compound by means of decarboxylation in the presence of BF3, EtjO, pyridine, or other materials. 

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