Protective group 9-anthrylmethyl

Protection of the nitrogen in 4 faced the classical N- versus O-alkylation selectivity issue, which was solved by selection of the solvent system. The original protecting group, pMB, was replaced with 9-anthrylmethyl (ANM), which provided the best enantioselectivity with the newly discovered asymmetric addition to the ketimine. 

Sodium methylmercaptide 9-Anthrylmethyl as protective group Removal from carboxyl... 

Anthrylmethyl as protective group 29, 3 Antimony chlorides 23, 544 suppl. 29... 

A soln. of 9-anthrylmethyl p-ethoxyphenylcarbamate and Na-methylmercaptide in dimethylformamide stirred 3 hrs. at -20° under dry Ng, then poured into aq. HCl-ice -> p-phenetidine. Y 91%. - Despite its easy removal by the above method, the protective group is resistant to various bases and acids. F. e. s. N. Kornblum and A. Scott, J. Org. Chem. 42, 399 (1977). 

This derivative is prepared from an A-protected amino acid and the anthrylmethyl alcohol in the presence of DCC/hydroxybenzotriazole. It can also be prepared from 2-(bromomethyl)-9,10-anthraquinone (Cs2C03). It is stable to moderately acidic conditions (e.g., CF3COOH, 20°, 1 h HBr/HOAc, / 2 = 65 h HCl/ CH2CI2, 20°, 1 h). Cleavage is effected by reduction of the quinone to the hy-droquinone i in the latter, electron release from the —OH group of the hydroqui-none results in facile cleavage of the methylene-carboxylate bond. The related 2-phenyl-2-(9,10-dioxo)anthrylmethyl ester has also been prepared, but is cleaved by electrolysis (—0.9 V, DMF, 0.1 M LiC104, 80% yield). ... 

Dioxo)anthrylmethyl esters, to protect carboxyl groups, 255-256... 

Anthrylmethyl can be readily attached, remains in place under a variety of circumstances, e. g. in acidified oxygen-containing solvents such as dioxane, and is readily removed under mild, highly specific conditions. - E 9-Anthrylmethyl mesitoate treated 30 sec. at 25° with Na-methylmercaptide in hexamethylphos-phoramide mesitoic acid. Y 93%. F. e. in dimethylformamide, also protection of phenols and mercaptans inch thiophenols, s. N. Kornblum and A. Scott, Am. Soc. 96, 590 (1974) protection of carboxyl groups as zl -oxazolines cf. A. I. Meyers et al., J. Org. Chem. 39, 2787 (1974). 

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