Mild and Selective Reagents for Cleavage of Protecting Groups

The reagents 1, which are Lewis acids, selectively cleave certain ether, ester and carbamate protecting groups under mild conditions.¹⁾ The relative reactivity of common protecting groups towards 1 was reported:^1a) MOMOR, MEMOR > BOC > CBZ, ^tBuOR > PhCH₂OR > CH₂=CHCH₂OR > ^tBuO₂CR, secondary alkylOR > PhCH₂O₂CR, primary alkylOR >> alkylO₂CR. The reagent 1b, which has lower reactivity than 1a, may be advisable when higher selectivity is required, for example, synthesis of natural products. Additionally, TBDMS, TBDPS and PMB ethers are not affected by 1.²⁾

MOM = Methoxymethyl
MEM = 2-Methoxyethoxymethyl
Boc = tert-Butoxycarbonyl
Cbz = Benzyloxycarbonyl
TBDMS = tert-Butyldimethylsilyl
TBDPS = tert-Butyldiphenylsilyl
PMB =　p-Methoxybenzyl