1- Oxycarbonyl- pyridine

By an analogous reaction sequence, 5-amino-5-deoxyxylopyranose derivative 494 was prepared2114 using 3-eyano-l,2-dihydro-N-(meth-oxycarbonyl)pyridine as starting material. 

CO, and methanol react in the first step in the presence of cobalt carbonyl catalyst and pyridine [110-86-1] to produce methyl pentenoates. A similar second step, but at lower pressure and higher temperature with rhodium catalyst, produces dimethyl adipate [627-93-0]. This is then hydrolyzed to give adipic acid and methanol (135), which is recovered for recycle. Many variations to this basic process exist. Examples are ARCO s palladium/copper-catalyzed oxycarbonylation process (136—138), and Monsanto s palladium and quinone [106-51-4] process, which uses oxygen to reoxidize the by-product... 

Pyridine-2-thione-A-oxycarbonyl (PTOC) derivatives of carboxylic esters 53 were developed by Barton et al. and serve as a convenient source of acyloxyl radicals, which upon decarboxylation provide specific routes to free radicals (equation 82). This process can also proceed by a radical addition (equation 83). Acyl selenides (54) are a convenient source of acyl radicals, which can undergo decarbonylation also giving specific free radicals (equation 84). ° ... 

The rate of the ring-opening reaction of 5, " and other substrates have been determined using an indirect method for the calibration of fast radical reactions, applicable for radicals with lifetimes as short as 1 ps/ This radical clock method is based on the use of Barton s use of pyridine-2-thione-Al-oxycarbonyl esters as radical precursors and radical trapping by the highly reactive thiophenol and benzeneselenol/ A number of radical clock substrates are known/ Other radical clock processes include racemization of radicals with chiral conformations, one-carbon ring expansion in cyclopentanones, norcarane and sprro[2,5]octane, a-and p-thujone radical rearrangements, and cyclopropylcarbinyl radicals or... 

Zur Reaktion von 2-Amino-3-mercapto-pyridin mit Triethoxy-essigsaure-ethylester zu 2-Eth-oxycarbonyl-(pyrido 2,3-d]-l,3-thiazol ) (46%) s.Lit.171. 

Another useful chain reaction involves the PTOC (pyridine-2-thione-N-oxycarbonyl) esters developed by Barton. Reaction of a carboxylic acid chloride (RCOCl) with the sodium salt on N-hydroxypyridine-2-thione produces an ester designated as R-PTOC. Addition of radical Y" (formed by an earUer initiation step) to the R-PTOC leads to the carboxy radical RCOj. The carboxy radical then decarboxylates to produce the radical R, which can continue the chain reaction or can undergo other reactions. 

Typical procedure. 6-N-Phthaloyl-2 -0-(9-phenylxanthen-9-yl)-5 -0-(fluoren-9-yl-metln-oxycarbonyl)adenosine 865 [628] To a solution of 864 (635 mg, 1 mmol) in dry pyridine (10 mL) was added dropwise a solution of Fmoc-Cl (336 mg, 1.3 mmol) in dry acetonitrile (5 mL). The reaction mixture was stirred for 4.5 h at room temperature and was then poured into cold, saturated sodium hydrogen carbonate solution (100 mL). The resulting mixture was extracted with chloroform (2 x 50 mL), the combined organic layers were concentrated in vacuo, and the residue was dried by co-evaporation with toluene (4 x 25 mL). It was then dissolved in dichloro-methane, and precipitation from cyclohexane gave 865 yield (717 mg, 82%) ... 

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