Triazenes special

Originally the triazenes were called diazoamino compounds, but in the present IUPAC nomenclature (1979) that term may be used only for a special group of triazenes (see Sec. 1.2). 

Solid-phase methods are applicable to syntheses of sequence-specific oligomers and dendritic structures. The triazene chemistry developed for this specific purpose may also be useful in other types of syntheses. Further development of solid-phase syntheses of this type into combinatorial synthesis of oligomers is the next logical step. Solid-phase methods will never completely replace solution-phase approaches to oligomers, but either technique should be considered with respect to the special characteristics and requirements for the system under investigation. 

Because of the special structural requirements of the resin-bound substrate, this type of cleavage reaction lacks general applicability. Some of the few examples that have been reported are listed in Table 3.19. Lactones have also been obtained by acid-catalyzed lactonization of resin-bound 4-hydroxy or 3-oxiranyl carboxylic acids [399]. Treatment of polystyrene-bound cyclic acetals with Jones reagent also leads to the release of lactones into solution (Entry 5, Table 3.19). Resin-bound benzylic aryl or alkyl carbonates have been converted into esters by treatment with acyl halides and Lewis acids (Entry 6, Table 3.19). Similarly, alcohols bound to insoluble supports as benzyl ethers can be cleaved from the support and simultaneously converted into esters by treatment with acyl halides [400]. Esters have also been prepared by treatment of carboxylic acids with an excess of polystyrene-bound triazenes here, diazo-nium salts are released into solution, which serve to O-alkylate the acid (Entry 7, Table 3.19). This strategy can also be used to prepare sulfonates [401]. 

A series of special linkers and cleavage strategies has been developed for the release of amines from insoluble supports (Table 3.23). These include the attachment of amines as triazenes, enamines, aminals, amidines, sulfonamides, sulfinamides, hydrazines, or amides. 

Under the triazene syntheses accomplished by building of nitrogen chains, the coupling of amides MNR R" (M = Li, Na) with aryidiazonium salts ArN2CI is worth special mention [Eq. (8)]. This reaction Preparation... 

Apart from numerous similar 3-lactam syntheses,the very promising photolytic [2 + 2] cycloaddition of imines (or the corresponding hexahydro-l,3,5-triazenes respectively)to chromium carbene complexes that leads to norcardicin precursors merits special interest. 

The specially developed photopolymers, particularly the triazene polymers,... 

Photosensitive polymers containing azo groups [235,236] or triazene groups [237] in the main chain also undergo main chain scission and evolve nitrogen upon UV irradiation. With respect to photochemistry, alkylaryl initiators are of special interest because they have better absorption characteristics than dialkyl initiators and are, on the other hand, more reactive than the respective diaryl-substituted compounds. 

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