Nucleophilic Cleavage of Oxime and Related Esters

A further type of linker, especially designed for facile nucleophilic cleavage, is the oxime linker. Oximes of resin-bound ketones or aldehydes can be acylated to yield O-acyl oximes, which are readily cleaved by a variety of nucleophiles (Table 3.14). A widely used support of this type is p-nitrobenzophenone oxime resin (Kaiser oxime 

Resin-bound 1-hydroxybenzotriazole (HOBt) has also been prepared [312-314], and yields, upon O-acylation, highly reactive esters [312,315,316], These are even cleaved by weak nucleophiles, such as anilines or even N-hydroxysuccinimide (Entry 7, Table 3.14). The reactivity of resin-bound HOBt esters is greater than that of resin-bound 4-acyl-2-nitrophenyl esters [296], Similarly, resin-bound /V-hydroxysuccinimide has also been used for the preparation of polymeric acylating agents (Entry 6, Table 3.14 [317-319]). 

Because of their sensitivity towards nucleophiles, O-acylated, resin-bound hydroxy-benzotriazoles and related compounds are not suitable for multistep synthetic 

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