Selective tert-Butyl Ester Deprotection in the Presence of Acid Labile Protecting Groups with Use of ZnBr₂

Abstract

Chemoselective hydrolysis of tert-butyl esters in the presence of other acid-labile groups has been explored by employing alpha-amino esters and ZnBr(2) in DCM. Although N-Boc and N-trityl groups were found to be labile, PhF protected amines were compatible with these Lewis acid deprotection conditions such that a variety of N-(PhF)amino acids were prepared in good yields from their corresponding tert-butyl esters.

Influence of a Metal Substrate on Small‐Molecule Activation Mediated by a Surface‐Adsorbed Complex

“…The TMS‐protected ethynyl group was introduced by Sonogashira cross‐coupling. Due to the lability of the TMS unit towards acids, the Boc protecting group was cleaved by ZnBr 2 in dichloromethane . Finally, the diphenylphosphine groups were introduced with chlorodiphenylphosphine in the presence of n BuLi …”

Amino Acid-Protecting Groups

“…t Bu esters can be selectively cleaved in its presence by using ZnBr 2 in DCM or trichloroacetic acid. 133,132 BrPhF is removed by Pd-catalyzed aminolysis with morpholine, followed by treatment of the resulting acid-labile morpholine adduct with DCA and triethylsilane (TES) in DCM.…”

MgI2‐Mediated Chemoselective Cleavage of Protecting Groups: An Alternative to Conventional Deprotection Methodologies

“…Then, mild non-transition-metal-assisted deprotections ystems of the most usual PGs of amines (trityl, [11,12] Z, [13][14][15] Boc [14,[16][17][18] )o rcarboxylic acids [19] (tert-butyl, [18,[20][21][22][23] benzyl [24][25][26][27][28] esters) were reported,b esides al ow effectivem ethod for allyl ester, [27] and none for the alloc PGs. [29] Here, we reasoned that Lewis acids in aproticm edium needed to be explored in am ore systematic way for their chemoselective potential, amino-acids being indeeda ni deal model of functional group diversity and for racemizations tudies.D uring our campaign to find selectivec onditions to cleave ethyl esters while preserving the Fmoc group, we discovered the impressivep otentialo f MgI 2 ,e nlarginga fterwards the scopet of acile chemoselective cleavages of various standardsP Gs or PS-resins( Figure 1).…”