Protecting moieties 4-nitrobenzyl

This approach offers unique opportunities for the generation of multi-functionalized cyclic 2-azadiene systems. A wide variation of the substitution pattern at the positions N-1 and C-6 can be determined by an appropriate choice of the aldehyde and amine. Various substituents can easily be introduced at the C-3 position via addition/elimination reactions on the sensitive imidoyl chloride moiety [24]. Upon reaction with bi-functional reagent, an adequately AT-protected 2(lH)-pyrazinone was elaborated into C-nucleoside analogues (Scheme 8). The desired skeleton and functionalities were obtained by oxidation-cyclization reaction followed by photochemical removal of the protective o-nitrobenzyl group [25]. 

Amino protecting groups fall into four broad categories nitrobenzyl (e.g., nitrobenzyloxy-carbonyl and 4,5-dimethoxy-2-nitrobenzyloxycarbonyl), phenacyl (e.g., 4-methoxyphen-acyloxycarbonyl), benzyloxycarbonyl (e.g., a,a-dimethyl-3,5-dimethoxybenzyloxycarbonyl), and arylsulfonamides (e.g., tosyl). All but the sulfonamides mask the amino group as a carbamate. Removal of the blocking moiety releases an unstable carbamic acid, which spontaneously decarboxylates to give the unprotected amine. 

Scheme 6.192 shows the o-nitrobenzyl moiety used as a photolabile linker in the solid-phase oligosaccharide synthesis on a polystyrene (PS) support.1208 After the synthesis of the protected oligosaccharide 404, PS attached to the photoremovable group is removed by photolysis and the final product is obtained by hydrogenolysis. Such a strategy could be promising for combinatorial synthesis of oligosaccharide libraries. 

A similar strategy of using photoactivation to cleave what may be viewed as protecting groups can similarly be used in the postsynthetic modification of MOFs. Cohen et al. demonstrated the use of a catechol-bearing terephthalic acid ligand, 2-((2-nitrobenzyl)oxy)terephthalic acid, into a MOF through the protection of the catechol moiety with nitrobenzyl... 

In addition to the alkene-functionalized polymer approach of making side-chain functionalized polymer, other approaches have also been reported. For example, based on the protection-deprotection chemistry of ortho-nitrobenzyl moiety, Barner-Kowollik and coworkers investigated light-triggered release of thiols at ambient temperature and developed a novel method to modify functionalization... 

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