Preparation of tert-Butyl 6-Aminopenicillanate and its 6-Oxo and 6-Diazo Derivatives

A 1:1 1,4-dioxane–tert-butyl acetate mixture and BF3 etherate were used for an effective 6-aminopenicillanic acid conversion into the tert-butyl ester (64±3% yield) which could be easily transformed into tert-butyl 6-oxo- and 6-diazo-penicillanates.