An efficient, one-flow Arndt–Eistert synthesis was demonstrated. A sequence of acid chloride formation–nucleophilic acyl substitution–Wolff rearrangement–nucleophilic addition was performed in a microflow system without isolating any intermediates, which included a potentially explosive compound. The microflow system was made from simple, inexpensive, and readily available instruments and tubes. α-Aryl esters 2a and 2b were prepared in yields of 33 and 23 % (three steps) respectively.