OXIDATION OF PHENOLIC AND HETEROCYCLIC AMINE SYSTEMS WITH DIPHENYLSELENIUM BIS(TRIFLUOROACETATE).

摘要

As part of an effort to design mild and selective two-electron oxidants for phenolic compounds, the new organoselenium(IV) reagent, diphenylselenium bis(trifluoroacetate) 1, was developed. Two basic oxidations of phenolic compounds with 1 were studied: oxidative aryl coupling and hydroxylation to form p-benzoquinone systems. The oxidation of secondary and tertiary amines was also investigated.;The addition of phenols, unsubstituted in the para position, to an excess of the reagent 1 and lithium trifluoroacetate gave yields of 60-82% of the p-benzoquinone. The skin allergen primin, 2-methoxy-6-pentyl-p-benzoquinone, was synthesized with this method in 80% yield from 2-methoxy-6-pentylphenol. Similarly, 2,6-dimethylaniline was oxidized to 2,6-dimethyl-p-benzoquinone in 72% yield.;Oxidation of the secondary and tertiary amine-nitrogen of 1,2,3,4-tetrahydroisoquinoline compounds, as well as 1,2,3,4-tetrahydro-(beta)-carboline, with the reagent 1 gave the corresponding 3,4-dihydro-compounds in greater than 80% yield. A 1-benzyl-1,2,3,4-tetrahydroisoquinoline compound and the (beta)-carboline could be oxidized further to the fully aromatic compounds in 75% and 61% yield, respectively. Oxidative decarboxylation of 3-carboxy-1,2,3,4-tetrahydroisoquinoline with the reagent 1 gave isoquinoline in 26% yield; 3-carbomethoxyisoquinoline was isolated as well in 40% yield after addition of diazomethane. The methyl ester of the acid and an analogous (beta)-carboline were dehydrogenated cleanly to the fully aromatic 3-carbomethoxy-compounds in 100% and 71% yield, respectively.;The reagent 1 offers a new method for the mild and selective two-electron oxidation of phenols and heterocyclic amine systems. It can be used in a stoichiometric fashion and is an improvement over many existing methods.;The two-electron oxidation of the 4-hydroxyphenyl moiety of some diarylalkanes resulted in electrophilic aromatic substitution of the second, electron-rich aryl ring to provide, overall, intramolecular oxidative phenolic coupling. Oxidation of 1-(3,4-methylenedioxyphenyl)-3-(4-hydroxyphenyl) propane and 1-(3-hydroxy-4-methoxyphenyl)-3-(4-hydroxyphenyl) propane gave the corresponding spirodienones in 76% and 65% yield, respectively. Ethyl 2-carboethoxy-2-(3,5-dimethoxy-4-hydroxybenzyl)-4-(3,4-methylenedioxyphenyl) butyrate was oxidized to a p-quinone methide intermediate; aryl-benzyl coupling gave 1-(3',5'-dimethoxy-4'-hydroxyphenyl)-2,2-dicarboethoxy-6,7-methylenedioxytetralin in 75% yield.