Procedure:  100 mL 1-neck flask, stirbar, septum, N₂ inlet

                  Prepared a suspension of 2.230 g of I in 20 mL of benzene and 10 mL of methanol.  Cooled to 0 C.  Added a 2.0 M solution of TMSCHN₂ in hexanes dropwise until most of the solid dissolved and gas evolution ceased.  TLC (EtOAc, UV) showed product spot at Rf 0.51.  The reaction mixture was filtered through Celite to remove unwanted solids.  The solvent was removed from the filtrate by rotary evaporation.  The product was a dark brown solid and was sufficiently pure at this stage for further elaboration. 

 

¹H NMR (CDCl₃, 300 MHz) d 9.42 (d, J = 1.3 Hz, ArH, 1H), 9.02 (d, J = 5.0 Hz, ArH, 1H), 8.04 (dd, J = 5.0, 1.3 Hz, ArH, 1H), 4.05 (s, COCH₃, 3H). 

 

notes

 

Trimethylsilyldiazomethane (TMSCHN₂) is a stable and effective alternative to diazomethane.  Carboxylic acids are readily converted to their methyl esters using this reagent in the presence of methanol at room temperature (see Hashimoto, N.; Aoyama, T.; Shioiri, T.  Chem. Pharm. Bull.  1981, 29, 1475).  The mechanism for the reaction has been postulated as follows.