A Simple Conversion of 1-Chloroethyl Carbonates to Fluoroformates: Value in the Preparation of Tertiary Alkyl Fluoroformates

Article abstract of DOI:10.1021/jo00293a032

When the economical and easily available 1-chloroalkyl carbonates (RCHClOCO2R') are heated neat or in solution with KF in the pesence of 18-crown-6 catalyst, they fragment to aldehydes (RCHO) and fluoroformates (FCO2R').If the system is evacuated during reaction and either or both products are removed as formed, then the process is driven to completion and fluoroformates are isolated in good yield.The new methodology (which exemplifies an unusual conversion of an ester to an acid halide) is especially valuable in the synthesis of important tertiary alkyl fluoroformates and benzyl fluoroformate (with R as CH3 in the carbonate): tert-butyl fluoroformate (BOC-F, 84percent yield), tert-amyl fluoroformate (83percent), 1-adamantyl fluoroformate (76percent), benzyl fluoroformate (60percent).Boc-F previously has been recommended as a superior reagent for the preparation of Boc-amino acids, but earlier routes to this reagent have been expensive and impractical.When R in the carbonate reactant is Cl3C, the reaction proceeds cleanly without the 18-crown-6 catalyst (Boc-F in 79percent yield).This latter variation is most useful on a small industrial scale.