Debenzylation, oxidative

When imines were applied in the cycloaddition/oxidafion sequence, the substituent on the nitrogen atom has to be removed to enable the aromatizafion reaction. In the case of imines generated from benzyl amine, the benzyl substitutent can be removed utilizing regular reductive deprotection techniques combined with oxidizing conditions for the general conversion of a dihydroarene into an arene. Such a cycload-dition/debenzylation/oxidation sequence has been realized by Colby et al. for the synthesis of pyridine derivatives such as 34 (Scheme 13.17) [18]. 

The oxazoloquinolinequinone derivative 610 was prepared from the allylphenol 605 which was transformed to the alcohol 606 and then to the aldehyde 607. Subsequent debenzylation gave 608 that was oxidized with Ce(NH4)2(N02)6 to the quinone 609 that upon cyclization with ethanolamine gave the oxazoloquinolinequinone 610 which showed... 

Oxidative coupling of o-nitrotoluene gives 4,4 -dinitrodibenzyl which is reduced with hydrogen to the diamine. The diamine is pyrolyzed to give dihydrobenzazepine. This is reacted with N-(3-chloropropvl)-N-methylbenzamine to give N-benzyldesipramine. This is debenzylated by reductive cleavage and then reacted with HCI. 

Quebrachitol was converted into iL-c/j/roinositol (105). Exhaustive O-isopropylidenation of 105 with 2,2-dimethoxypropane, selective removal of the 3,4-0-protective group, and preferential 3-0-benzylation gave compound 106. Oxidation of 106 with dimethyl sulfoxide-oxalyl chloride provided the inosose 107. Wittig reaction of 107 with methyl(triphenyl)phos-phonium bromide and butyllithium, and subsequent hydroboration and oxidation furnished compound 108. A series of reactions, namely, protection of the primary hydroxyl group, 0-debenzylation, formation of A-methyl dithiocarbonate, deoxygenation with tributyltin hydride, and removal of the protective groups, converted 108 into 7. 

A convenient procedure for the lactonization of alkenols has been recently revealed by Borhan and coworkers [19]. This methodology was successfully applied in the total synthesis of (+)-tanikolide (7-37), a natural product of marine origin which exhibits antifungal activities. Thus, when alkenol 7-36 is subjected to soluble oxone and a catalytic amount of 0s04, a smooth domino oxidative cleavage/lactonization process takes place which leads, after debenzylation, to the desired product in good overall yield (Scheme 7.12). 

Buchwald-Hartwig amination of iodobenzene 92 with 2-benzyloxy-4-methyl-aniline 93 affords the diarylamine 94 in high yield (Scheme 32). In this case the Goldberg coupling gives poor yields. Oxidative cyclization of compound 94 using stoichiometric amounts of palladium(II) acetate in acetic acid under reflux leads to the carbazole 95, which by reductive debenzylation provides... 

First phosphitylation was performed by 0-benzyl-bis(iV,iV,-diisopropyl)-phosphoroamidite in the presence of diisopropyl-ammonium tetrazolide at room temperature in dichloromethane solution (step a). The intermediate phosphoroamidite was coupled with a glycerol moiety in the presence of tetrazole in boiling CH2CI2 to give the benzyl phosphite (step b), which was oxidized by CPBA in CH2CI2 into the corresponding phosphate (step c). In the final step d total debenzylation was achieved by Pd/C transfer hydrogenol-ysis in the presence of formic acid and methanol at room temperature. 

This method has been extended to include 1,3-diarylthioureas which are benzylated and then treated with phenylisocyanate to give S-benzylisothiobiurets (252). Oxidative debenzylation with... 

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