Dimedone amine protection

Allyl carbonate esters are also useful hydroxy-protecting groups and are introduced using allyl chloroformate. A number of Pd-based catalysts for allylic deprotection have been developed.209 They are based on a catalytic cycle in which Pd° reacts by oxidative addition and activates the allylic bond to nucleophilic substitution. Various nucleophiles are effective, including dimedone,210 pentane-2,4-dione,211 and amines.212... 

The Dde-protected amino acids are readily synthesized by acylation of dimedone (5,5-dimethylcyclohexane-l,3-dione) with acetic acid (DCCyDMAP activation), followed by condensation with the primary amine, e.g. Fmoc-Lys-OH, in refluxing ethanol for 60 hours, affording the orthogonally protected amino acid 24 (Scheme 9). 

The mild and selective nature of the palladium-catalysed allylation reaction has made it suitable for protection. Allyl ethers, esters, amines and carbamates can usually be easily formed by standard procedures. The allyl group can be removed later by exposme to a palladium catalyst and a competitive nucleophile, Y (Scheme 9.68). This is an allyl transfer reaction. Commonly used competitive nucleophiles for allyl esters of carboxylic acids include sodium 2-methylhexanoate, secondary amines such as pyrrolidine (Scheme 9.69) and morpholine, and dimedone. ... 

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