Continuous flow organocatalyzed methoxycarbonylation of benzyl alcohol derivatives with dimethyl carbonate

An organocatalytic continuous flow process is presented for the preparation of non-symmetric benzyl carbonate derivatives. The procedure relies on dimethyl carbonate as a reagent and a solvent in conjunction with an organocatalyst for the selective methoxycarbonylation of diversely substituted benzylic alcohols. The reaction is optimized with benzyl alcohol as a model substrate, which emphasizes 1,4-diazabicyclo[2.2.2]octane (DABCO), 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD), 2,8,9-trimethyl-2,5,8,9-tetraaza-1-phosphabicyclo[3.3.3]undecane (Verkade's base) and phosphazene base P-2-Et as suitable organocatalysts. The optimized conditions are next extended to a small library of 18 structurally diverse benzylic alcohol derivatives. High conversion (66-96%) and total selectivity (>99%) are achieved under mild conditions and short residence time, which converge toward a versatile and robust continuous flow protocol. Then, we illustrate that a set of representative benzyl methyl carbonates can be considered as stable, low toxicity surrogates of the corresponding chloroformates for the preparation of valuable benzyl N-hydroxycarbamates.

Automated summary

An organocatalytic continuous flow process for the preparation of non-symmetric benzyl carbonate derivatives is presented. The optimized conditions achieved high conversion and total selectivity, making it a versatile and robust method with potential applications.