1-adamantyl nitrate

Dinitrogen pentoxide reacts with alkanes in carbon tetrachloride at 0 °C via a radical mechanism to give nitration products which can include nitrate esters.Reactions of alkanes with dinitrogen pentoxide in nitric acid are complex and of little synthetic value. 1-Adamantyl nitrate is one of the products obtained from the photochemical irradiation of a solution of adamantane and dinitrogen pentoxide in methylene chloride. ... 

No oxidation of alcohols is observed under the reaction conditions. The N-nitrocollidinium salt is generally less reactive than nitronium tetra-fluoroborate itself, but gives better control of conditions and superior yields as shown, for example, in the preparation of 1-adamantyl nitrate. Adamantanol gives less than 2% yield of nitrate ester upon treatment with nitronium tetrafluoroborate while the N-nitro salt forms the ester in 82 yield. 

A soln. of 1-adamantyl nitrate in acetonitrile added at 40° to 95%-H2S04 1-... 

Nitration and adamantylation of the pyrazolo[3,4-c][l,2,5]oxadiazole 96 has been demonstrated, yielding 97 and 99 respectively. The alkylated derivatives 98 were formed by way of the sodium salt 100 (Scheme 6) <2003T1059>. 

This dichotomy is quite evident in the reaction of cydooctane with nitronium trifluoroacetate. The products obtained were cyclooctyl triflu-oroacetate, cyclooctyl nitrate and nitrocydooctane. Conversion of adaman-tane to 1-fluoroadamantane in 95% 3ueld on reaction with nitronium tetrafluoroborate in pyridine polyhydrogen fluoride indicates that formation of adamantyl cation by formal hydride abstraction is a significant alternative to the nitration-protodenitration pathway. 

The nitration occurred with ease and high positional selectivity at the bridgehead to give 1-nitroadamantane as the major product (Equation 5.56). The best result was obtained at -78 °C in the presence of a large excess of NO, when tertiary/secondary positional selectivity was as high as 100. Skeletal rearrangement was not observed. Formation of nitrates (4-5%) in Equations (5.58) and (5.59) may be attributed to the oxidation of the initially formed adamantyl radicals to carbocations, followed by coupling with the nitrate ion. 

Mechanistically, the reactions of adamantane and ethers with NO are rationally explained by considering the formation of carbocations as transient intermediates (Scheme 6.14). The generation of PINO from NHPI in the presence of NO is confirmed by ESR measurements [170], but the formation of PINO by this method may be due to traces of NO2 contained in the reaction system. On the other hand, Suzuki has suggested the formation of a cationic species via a diazonium nitrate in the nitration of alkenes with N O [ 17 5 ]. The nucleophilic attack of the benzonitrile and water on the adamantyl and benzylic cations would result in the amide and aldehyde, respectively [170]. 

Synthesis of compound 68 by oxidative decarboxylation of adamantane carboxylic acid is described in [25], Initially, for the synthesis of 2-(l-adamantyl)benzimidazole (68), adamantan radical was obtained in sulphuric acid diluted by silver nitrate in the presence of ammonia persulfate. Then, the synthesized radical was inserted directly into the heterocycle. After N-methylation, 2-(l-adamantyl)benzimidazole (68) was transferred in l-methyl-2-(l-adamantyl)-benzimidazole (79). The experiments carried out on chicken embryo revealed high antiviral activity of both obtained compounds [25] ... 

In 1984, Tsupak and co.[64] synthesized 2-(l-adamantyl)benzimidazole (68) with 45% yield by substitution of sulpho group in benzimidazole-2-sulfonic acid with adamantly radical. The reaction was carried out in aqua acetonitrile solution. The adamantyl radical was obtained by oxidativ decarboxylation of adamantanecarboxylic acid with ammonia persulfate in silver nitrate aqua solution. 

They have further studied the nitration reaction of 5(6)-(l-adamantyl)benzimidazole [95, 96]. The positive inductive effect of the adamantyl radical leads to an increase in electron density in the corresponding ortho positions, i.e. in positions 4 and 6 of the benzimidazole ring. This explains the formation of a mixture of isomers 153 and 154 as a result of the nitration reaction. 

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