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Acids Cleavable by Transition Metal Catalysis

4 Linkers for Acids Cleavable by Transition Metal Catalysis [Pg.54]

Benzyl alcohol linkers, such as those described in Section 3.1.1.1, can also be cleaved by palladium-catalyzed hydrogenolysis. Carboxylic acids have, for example, been obtained by hydrogenolysis of insoluble benzyl esters with Pd(OAc)2/DMF/H2 [89,161]. Resin-bound benzylic carbamates [162,163] and amides [164] can also be released by treatment with Pd(OAc)2 in DMF in the presence of a hydrogen source, such as 1,4-cyclohexadiene or ammonium formate. These reactions are quite surprising, because they require the formation of metallic palladium within the gelated beads. [Pg.54]

The two most commonly used types of allyl alcohol linker are 4-hydroxycrotonic acid derivatives (Entry 1, Table 3.7) and (Z)- or ( )-2-butene-l, 4-diol derivatives (Entries 2 and 3, Table 3.7). The former are well suited for solid-phase peptide synthesis using Boc methodology, but give poor results when using the Fmoc technique, probably because of Michael addition of piperidine to the a, 3-unsaturated carbonyl compound [167]. Butene-l,4-diol derivatives, however, are tolerant to acids, bases, and weak nucleophiles, and are therefore suitable linkers for a broad range of solid-phase chemistry. [Pg.55]

Entry Loaded resin Cleavage conditions Product, yield (purity) [Pg.55]




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Catalysis by transition metals

Catalysis transition metal

Cleavability

Transition catalysis

Transition metal-catalysis metals

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