P-Nitrobenzophenone

The polymer-bound p-nitrobenzophenone oxime (71d) has been found to be a suitable support for stepwise peptide synthesis. Protected peptides can be assembled on 70d by coupling and deprotection steps similar to those employed in the usual Merrifield solid-phase procedures (Scheme 39). Cleavage of peptides from 71d can be accomplished with hydrazine and amino acid esters under mild conditions, which do not affect benzyl ester side-chain protecting groups. 

Problem 15.18 Prepare the following compounds from benzene, toluene, and alcohols of four or fewer C s (a) 2-methylpropanal (isobutyraldehyde), (b) p-chlorobenzaldehyde, (c) p-nitrobenzophenone (p-NOjCftH4COC,.H,), (d) benzyl methyl ketone, (e) p-methylbenzaldehyde. ... 

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... 

In the case of asymmetric diaryl ketones, migration of aryl groups with electron-donating substituents occurs preferentially . For instance, p-methoxybenzophenone affords 96% of (4-methoxy)phenyl benzoate by oxidation widi trifluoroperacetic acid, whereas p-nitrobenzophenone under the same reaction conditions gives 95% of phenyl 4-nitrobenzoate. 

ChHj.OjNo p-Nitrobenzophenon-a-oxim-O-mcthylather (Xj) —CjH, Benzol (X,) [12] (K3, d4)... 

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