Synthesis of [1‐13C]‐para‐xylene and [2‐13C]‐para‐xylene

An efficient synthesis of 1‐¹³C]‐para‐xylene ( 1a ) and 2‐¹³C]‐para‐xylene ( 1b ) is described. The incorporation of the label has been achieved by cyclocondensation of suitable 1,5‐bis(bromomagnesio)alkanes with either ethyl 1‐¹³C]acetate or ethyl ¹³C]formate which gave ring‐¹³C]‐labelled dimethylcyclohexanols. Dehydration of these alcohols followed by dehydrogenation of the intermediate dimethylcyclohexenes furnished the title compounds in 32 and 40% overall yield, respectively. Copyright © 2001 John Wiley & Sons, Ltd.