Adams catalyst esters

Because of the possibility of racemization during the transesterification reaction (strong basic conditions) alternative methods are reported. These include transesterification in the presence of the KF/18-crown-6 ether 461 or the use of titanium tetraalkoxides. 471 The methods are efficient and represent a route to any required dialkyl ester using diphenyl esters as starting materials. Diphenyl groups can also be removed by hydrogenation in the presence of platinum dioxide (Adams catalyst) to provide the free phosphonic acid moiety directly)46 ... 

The main problem here is removing the phenyl ester groups from the phosphonic moiety.We have found that convenient routes for deblocking are hydrogenation on Adams catalyst and transesterification methods followed by hydrogen bromide in glacial acetic acid treatment. The best results ewre obtained if transesterification was carried out using potassium fluoride-crown ether-methanol system. 

Catalytic hydrogenation of fluoro- and difluOTO-m- and tran -butenedioic acids and their esters frequently affords products only of hydrogenolysis, especially when platinum oxide (Adams catalyst) is used. Hydrogenolysis is favored in polar solvents, and is found to be more effective when rhodium or nickel rather than palladium are used as the catalysts (Table 2). Hydrogenolysis takes place prior to the saturation of the double bonds fluoro- and 2,3-difluoro-succinic acids do not suffer any loss of fluorine under the same reaction conditions. ... 

The unsaturated ester (1-2 mg) in a test-tube is dissolved in methanol (1 mL) and Adams catalyst (platinum oxide 1 mg) is added. The tube is connected via a two-way tap to a reservoir of hydrogen e.g. in a balloon or football bladder) at or just above atmospheric pressure and to a vacuum pump. The tube is alternatively evacuated and flushed with hydrogen several times to remove any air, then it is shaken vigorously while an atmosphere of hydrogen at a slight positive pressure is maintained for 2 hr. At the end of this time, the hydrogen supply is disconnected, the tube is flushed with... 

To complete the total synthesis of myrrhine 420, we needed an adequate epimerization of the stereocenter of the common intermediate 425. As illustrated in Scheme 12.110, we elected to pursue an aromatization-reduction sequence by treating aza-tricycle 425 with DDQ, and the ensuing pyridinium salt438 was hydrogenated over Adams catalyst in AcOH to give the all-sy aza-tricycle 439 in 54% yield for the two-step protocol as a 2 1 mixture of diastereomers with respect to the ester group. 

Binaphthol- and biphenyl-derived ketones (9 and 10) were reported by Song and coworkers in 1997 to epoxidize unfunctionalized alkenes in up to 59% ee (Fig. 3, Table 1, entries 9, 10) [37, 38]. Ketones 9 and 10 were intended to have a rigid conformation and a stereogenic center close to the reacting carbonyl group. The reactivity of ketones 9 and 10 is lower than that of 8, presumably due to the weaker electron-withdrawing ability of the ether compared to the ester. In the same year, Adam and coworkers reported ketones 11 and 12 to be epoxidation catalysts for several trans- and trisubstituted alkenes (Table 1, entries 11,12). Up to 81% ee was obtained for phenylstilbene oxide (Table 1, entry 25) [39]. 

Similar to p-keto esters, P-keto amides may be readily hydrogenolyzed by conditions. Thus, 3-acyloxyindole (10), a P-keto amide, is cleanly hydrogenolyzed to the corresponding 3-alkyl derivative in ethanol over Adams palladium oxide catalyst (eq. 5.37).126... 

Platinum catalyst (Adams), in oxidation of carbohydrate sulfonic esters, 258 Poisson distribution, 304 Polarimetric measurement, of mutarota-tion, 47,52... 

Although the exchange of the hydroxyl hydrogen in methanol with deuterium in various deuterium compounds such as deuterium oxide and deuterium sulfide has been reported 1-3) and the preparation of methanol-d (CH3OD) by the saponification of esters and decomposition of Grignard reagent with deuterium oxide has been described 4 6), the catalytic exchange of deuterium gas with methanol over Adams platinum catalyst has not been previously studied. 

Phthalazine (21) and the half adamantyl ester of oxalic acid gave l-(adamant-l-yl)phthalazine (24) [reactants, (F3CC02)2lPh (as catalyst), PhH, reflux, h 33% mechanism discussed]. ... 

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