3 ,5 -Dimethoxybenzoin carbonates

Pirrung, M. C. and Bradley, J.-C., Dimethoxybenzoin carbonates photochemically removable alcohol protecting groups suitable for phosphoramidite-based DNA synthesis, /. Org. Chem., 60, 1116-1117, 1995. 

The DMB carbamate can also be introduced through the 4-nitrophenyl carbonate. " It has been prepared from an isocyanate and 3, 5 -dimethoxybenzoin. The synthesis of a number of other substituted benzoins as possible protective groups has been described. ... 

Importantly, TV-carbamoyl derivatives of primary amines obtained from photolabile benzoins exist in varying proportions as cyclic hydroxyoxazolidinone tautomers. Therefore, the preparation of TV-carbamoyl derivatives of benzoins is applicable only for secondary amines and TV-alkylated amino acids. 244 At basic pH unsymmetrical benzoins, such as 3,5-dimethoxybenzoin, their mixed carbonate and carbamate derivatives, tend to equilibrate to the isomeric forms. Nevertheless, in TFA and aqueous solutions at pH 8 the structural integrity is fully maintained. 244 Preparation of 3,5-dimethoxybenzoin-derived carbamates of secondary amines and amino acids can be mediated by either CDI/methyl triflate in ni-tromethane 246 or 4-nitrophenyl chloroformate/DMAP in dry THF. 244 ... 

Dimethoxybenzoin (DMB) carbonates (39) were found to be photochemically removable alcohol protecting groups. DMB carbonates can be installedby the carbamate product (38) of DMB-OH (37) and iV,iV -carbonyldiimidazole activated by methylation (eqs 32 and 33). ... 

In 1995, Pirrung and Bradley " reported the use of dimethoxybenzoin (DMB) carbonate to protect various alcohols, including the 5 -hydroxyl group of nucleosides. The DMB carbonate was synthesized in three steps, starting with methylation of carbonyldiimidazole with methyl triflate followed by addition of 2-(3,5-dimethoxyphenyl)-2-hydroxy-l-phenylethanone to form a relatively stable activated acylating agent. Treatment with an alcohol under basic conditions in nitromethane furnished the protected alcohol 72 in yields that ranged from 42 to 95%. 

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