2.4- Diphenyl-6- -pyridine formation

The favored formation of a nucleoside 3 -(alkyl phosphate) was observed on treating the diphenyl phosphate anhydride of uridine 2, 3 -cyclic phosphate with benzyl alcohol.273 In a somewhat related reaction, on treatment with dicyclohexylcarbodiimide in aqueous pyridine, adenosine 2 (3 )-phosphate gave, initially, the 2, 3 -cyclic phosphate, which, on further reaction with the diimide, gave a mixture of the N-phosphonourea nucleoside 44 and its 2 -isomer, in unequal amounts.269 This type of reaction does not seem to occur with... 

Reactions with methylphenylcyclopropenone (154) provided an opportunity to compare the reactivities of the two different C—CO bonds. The reaction of 2-aminopyridines with methylphenylcyclopropenone (154) proceeded more slowly than with the diphenyl analog (153). In ether, formation of the ds-2-oxopyrido[l,2-a]pyrimidines (158 R1 = Me) and/or the imidazo[l,2-c<]pyridines (162) was observed, indicating that the cycloaddition proceeds via cleavage of the PhC—CO bond. The methyl-substituted trans-2-oxopyrido[l,2-a]pyrimidine (160 R1 = Me) was only detected in the reaction mixture of 2-amino-3-methylpyridine, where the H NMR spectrum exhibited signals assigned to 160 (R1 = Me, R = 9-Me). The compound was not isolated. The imidazo[l,2-a]pyridines (162) readily hydrolyzed to the acids (163), work-up therefore leading mainly to isolation of the acids. 

Reactions of 1,2,4-thiadiazoles with radicals and electron deficient species are virtually unknown. Catalytic and dissolving metal reductions usually result in S—N bond cleavage. For example, the 5-anilino-3-hydroxy derivative (51) gives a good yield of l-phenyl-2-thiobiuret (52) on Zn-HCl reduction (Scheme 27). Reduction of the diamino derivative (53) gives amidinothiourea (54) from which it may be prepared by oxidation (Scheme 28). Under similar conditions, cleavage of the 3,5-diphenyl derivative (55) results in loss of sulfur and formation of benzylbenzamidine (56 Scheme 29). Reduction of 5-alkylamino-or 5-arylamino-3-alkylthio derivatives (57) with H2S in pyridine-triethylamine or sodium in liquid ammonia yields 1-substituted dithiobiurets (58 Scheme 30). 

In the reaction of 3,5-dimethyl-2,6-diphenylpiperid-4-one oxime (10) with acetylene and RbOH-DMSO, migration of the 3a-Me group to the anionic nitrogen atom occurred, leading to 5,7-dimethyl-4,6-diphenyl-4,5,6,7-tetrahydropyrrolo[3,2-c]pyridine (11) (04CHE326). The formation of the N-anion caused aromatization of the tetrahydropyridine ring. Tetrahydropyrrolo[l,2-c]pyrimidine 12 resulted from the decomposition of the intermediate 3H-pyrrole in a retro-Mannich reaction (Scheme 3). 

Cleavage of perhydro-imidazo[l,2-a]pyridine (211) with diisobutyl-aluminum hydride produces 1,4-diazacyclononane (82TL4I8I). Addition of phenylmagnesium bromide to 2-phenyl-6,7,8,8a-tetrahydro-3//,5//-imi-dazo[l,2-a]pyridin-l-oxide (224) resulted in the formation of 2,2-diphenyl-perhydro-imidazo[l,2-a]pyridin-l-ol (225) (83AP47). 

Photo-oxidation of olefins in pyridine solution in the presence of FeCIs has been found to take one of three courses, depending on the substitution pattern of the substrate olefin. These routes lead to formation of a-chloroketones, gem-dichloroketones, and a,-dichloroketones, and have all been illustrated by their use in actual syntheses. a-Chloroketones have also been produced by irradiation of pyridine solutions of vinylsUanes or vinyl sulphides under similar conditions. DCA-sensitized photo-oxidation of l,2-diphenyl-3,3,4,4-tetramethylcyclobutene in MeCN leads to the corresponding ozonide in a process which occurs by initial formation of an oxirane. Jasmine lactone (12 ... 

The poor reaction with C-terminal proline most likely stems from the fact that proline cannot form the necessary oxazolinone for efficient reaction with the isothiocyanate. Work in our laboratory has obviated the need for oxazolinone formation by the use of diphenyl phosphoroisothiocyanatidate and pyridine. Reaction of this reagent with C-terminal proline directly forms the acylisothiocyanate. Once the acylisothiocyanate is formed, the addition of either liquid or gas phase acid followed by water was... 

The formation of alcohols or ethers is favored by low current densities, porous graphite as anode material, a solvent such as water/pyridine instead of methanol, a pH of the electrolyte above 7 and anions, such as bicarbonate, sulfate or perchlorate, as additives. Electron-donating substituents at C-2 of the carboxylic acid favor the oxidation of the intermediate radical. Thus a-alkyl, a-cycloal-kyl207,208 a-chloro, a-bromo, a-amino, a-alkoxy, a-hydroxy, a-acyloxy and a,a-diphenyl substituents more or less promote the formation of nonKolbe products. 

Fig. 11.— Lower Curve Mutarotation of n-Galacturonic Acid Phenylhydrazone (pyridine-ethanol, 1 1 by vol.) Upper Curve n-Galacturonic Acid Af.AT -Diphenyl-formazan Formation.

The yields of the pyrimidines 147 and the pyridines 151 are not high and vary greatly, depending on the structure of the starting materials. The latter can also determine the nature of the product. Thus, a mixture of 2,4-dimethyl-6-phenylpyrimidine, 2,4-dimethyl-4,6-diphenyl-4//-l,3-oxazine and 1-chloro-l-phenylethene was obtained by refluxing a 1 3 3 ratio of the acetophenone-benzonitrile-phosphorus oxychloride mixture, followed by treatment of the crude product with sodium carbonate solution .It has been shown that addition of an additional ketone molecule to the iminium intermediate is an alternative to the formation of the A -acylenamines and this route is catalyzed by aluminum chloride. Auricchio and coworkers believe also that the reaction of ketones with nitriles catalyzed with both protic and Lewis acids must be considered as a Ritter reaction (see, however, Section V.C). The cationic intermediate 152 thus formed can undergo either a proton shift giving enamide 153 or addition of another ketone molecule... 

---