An improved method for the protection of carboxylic acids as 1,1-dimethylallyl esters
(Chemical Equation Presented) 1,1-Dimethylallyl (DMA) esters of various N-protected amino acids have been synthesized using prenyldimethyl-sulfonium tetrafluroborate, a reagent that can be readily made and stored, in conjunction with catalytic CuBr. These reactions were complete within several hours and afforded DMA esters in high yields. As has been previously shown in our group, DMA esters represent a palladium-labile proctecting group for carboxylic acids that resists nucleophilic attack as a tert-butyl ester would.
Sedighi, Minoo,Calimsiz, Selcuk,Lipton, Mark A.
p. 9517 - 9518
(2007/10/03)
A convenient, general synthesis of 1,1-dimethylallyl esters as protecting groups for carboxylic acids
(Chemical Equation Presented) Carboxylic acids were converted in high yield to their 1,1-dimethylallyl (DMA) esters in two steps. Palladium-catalyzed deprotection of DMA esters was shown to be compatible with tert-butyl, benzyl, and Fmoc protecting groups, and Fmoc deprotection could be carried out selectively in the presence of DMA esters. DMA esters were also shown to be resistant to nucleophilic attack, suggesting that they will serve as alternatives to tert-butyl esters when acidic deprotection conditions need to be avoided.
Sedighi, Minoo,Lipton, Mark A.
p. 1473 - 1475
(2007/10/03)
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