Preparation of carbon-14 labeled 3,4-dihydro-5-methyl-1(2H)-isoquinolinone

Carbon‐14 labeled 3,5‐dihydro‐5‐methyl‐1(2H)‐isoquinolinone, a potent inhibitor of poly(ADP‐ribose) polymerase (ADPRP) was prepared from 1‐bromo‐2‐methylbenzene in 7.8 % overall yield. The C‐14 label was introduced from Ba14CO3 via metal‐halogen exchange and carboxylation reactions. Subsequent transformations yielded a propenecarbonyl azide 8 which was rearranged by Curtius reaction to the isocyanate, and a cyclization produced 5‐methyl‐1(2H)‐[4‐14C]isoquinolinone (9). From the compound 9 by Pd/C catalyzed hydrogenation 3,4‐dihydro‐5‐methyl‐1(2H)‐[4‐14C]isoquinolinone (10) was made.