Allyloxycarbonyl palladium

O Dangles, F Guibe, G Balavoine, S Lavielle. A Marquet. Selective cleavage of the allyl and allyloxycarbonyl groups through palladium-catalyzed hydrostannolysis with tributyltin hydride. Application of the selective protection-deprotection of amino acid derivatives and in peptide synthesis. J Org Chem 52, 4984, 1987. 

F.Guibf and Y. Saint M Leux, The allyloxycarbonyl group for alcohol protection Quantitative removal or transformation into allyl protecting group via w-allyl complexes of palladium, Tetrahedron Lett. 22 3391 (1981). 

Deprotection of allyl or allyloxycarbonyl derivatives of amino acids.1 This combination of reagents effects rapid reductive cleavage of allyl or allyloxycarbonyl derivatives of amino acids in CH2C12 containing a proton donor (p-N02C6H50H, acetic add, H20). The actual catalyst is probably bis(triphenylphosphine)palladium(0). Benzyl, Boc, and Cbo groups are stable to these conditions. This cleavage does not induce racemization. 

As an example, a new palladium based method has been developed for the alkylation of tyrosine residues [34], In this reaction, allylic carbonates, esters, and carbamates are activated by palladium(O) complexes in aqueous solution, resulting in the formation of electrophilic zr -allyl complexes (such as 16), Fig. 10.3-8(a). These species react at pH 8-10 with the phenolate anions of tyrosine residues, resulting in the formation of aryl ether 17 and regeneration of the Pd(0) catalyst. The reaction requires no organic cosolvent, is catalytic in palladium, and requires P(m-QjH4S03 )3 as a water-soluble phosphine ligand. In contrast to alkyl or allylic halides, the inert character of the allyloxycarbonyl compounds used in this reaction ensures that nonspecific... 

It has been reported that A -allyloxycarbonyl-protected hydrazines, including (90), react with a palladium(O) catalyst and Bu"3SnH to give versatile intermediate tin carbamates (91) that can be converted either into the corresponding deprotected or acylated hydrazines (Equation (17)) <91TL6629>. 

Alternatively, the C5 hydroxy group can be protected as 5-0-allyloxycarbonyl derivative instead (not shown in Scheme 29.6.1). This is done by reaction of abamectin with allylchloroformate and tetraethylendiamine in t-butyl methyl ether. In this case, the C5 hydroxy group can be deprotected in the last step by treatment with sodium borohydride in ethanol in the presence of catalytic amounts of tetrakis(triphenylphosphine)palladium. 

Other Alkyl and Aryl Ethers.- Procedures for the selective removal of allyl ether in the presence of allyloxycarbonyl ester protecting groups, or vice versa, using palladium and iridium catalysts have been published in full (cf. Vol.19, p.l5). A reference to ester migration during 0 -allylatlon is covered in Chapter 7. 

N-Allyloxycarbonyl functions can be efficiently removed by treatment with a palladium(O) catalyst [Pd (dba). CHCl,] and formic acid (3-4 equivalents) at 30 °C in THF. The method... 

Protocol 21. Alternative on-resin palladium-mediated allyloxycarbonyl and allyl deprotections ... 

Allyloxycarbonyls (Alloc or AOC) are useful protecting groups especially for primary amines (for a review see Ref. [131]). As they are easily cleaved-off in the presence of a suitable palladium catalyst, they have found widespread interest in peptide, oligonucleotide, and glucopeptide synthesis ever since they were introduced. Various sources for the nucleophile have been reported. They might consist of tin hydride, formic acid salts, ... 

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