Yield:-

Reaction Conditions:

Stage #1:3-amino-4-methyl-2-thiophenecarboxylic acid methyl ester with hydrogenchloride;sodium nitrite in water at 0; for 1 h;
Stage #2: with hydrogenchloride;copper(l) chloride in water at 0 - 20;Further stages.;

References:

Kochanny, Monica J.;Adler, Marc;Ewing, Janice;Griedel, Brian D.;Ho, Elena;Karanjawala, Rushad;Lee, Wheeseong;Lentz, Dao;Liang, Amy M.;Morrissey, Michael M.;Phillips, Gary B.;Post, Joseph;Sacchi, Karna L.;Sakata, Steven T.;Subramanyam, Babu;Vergona, Ron;Walters, Janette;White, Kathy A.;Whitlow, Marc;Ye, Bin;Zhao, Zuchun;Shaw, Kenneth J. [Bioorganic and Medicinal Chemistry,2007,vol. 15,# 5,p. 2127 - 2146]