Deprotection allyloxycarbonyl protecting groups

More recently Kunz and co-workers described a synthesis of 2,6-dideoxy-2,6-diaminopyra-noside libraries [73]. The scaffold 120 allows for selective deprotection of four positions in a manner that is independent of the sequence (O Scheme 11). Different functional groups have been incorporated at each position to give 121-4, which can then be cleaved from the solid support. For example, the 2-A-allyloxycarbonyl protecting group of 120 can be selec-... 

A SPOS approach to DNA synthesis was reported very recently. It involves a ten-step synthesis of a phosphoramidite building block of I -aminomethylthymidine starting from 2-deoxyribose [46]. Microwave-mediated deprotection of a corresponding N-allyloxycarbonyl (alloc-) protected nucleoside and acylation with the residue of pyrene-l-ylbutanolic acid (pyBA) were described (Scheme 16.25). Removal of the alloc protecting group was achieved on a support (controlled pore glass, cpg) under microwave conditions (80 °C, 10 min) to ensure full conversion. 

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. 

Another useful strategy for the activation of an amide towards hydrolysis involves intramolecular 0-alkylation of the amide carbonyl. An early rendition of this strategy entailed the use of 4-chlorobutanamides in which cleavage was initiated by treatment with silver(I) perchlorate in aqueous acetone. More re-cently the Fraser-Reid group showed that N-pent-4-enoyl derivatives are rapidly and efficiently cleaved under mild conditions by brief treatment with 3 equivalents of iodine in aqueous THF [Scheme 8.29]. These deprotection conditions do not affect oxidisable functionalities including p-methoxybenzyl ethers and alkyl sulfides though allyloxycarbonyl groups appear to be incompatible. Primary and secondary amines are readily protected as N-pent-4-enoyl derivatives by reaction with pent-4-enoic anhydride. 

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. 

Palladium-catalyzed Deprotection Processes. Several palladium-catalyzed and mild methods for the deprotection of various functional groups have been developed. For example, a system for the conversion of hydrazones into the corresponding carbonyl compounds that is catalytic in both Pd(OAc)2 and SnCl2 has been reported, as has a procedure for the Pd(OAc)2-catalyzed cleavage of allyloxycarbonyl (Alloc) protected alcohols. ... 

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