Cross-coupling methods for the large-scale preparation of an imidazole-thienopyridine:: Synthesis of [2-(3-methyl-3H-imidazol-4-yl)thieno[3,2-b]pyridin-7-yl]-(2-methyl-1H-indol-5-yl)-amine

The multihundred-gram synthesis of [2-(3-methyl-3H-imidazol-4-yl)-thieno[3,2-b]pyridin-7-yl]-(2-methyl-1H-indol-5-yl)- amine (1) is described utilizing a Stille cross-coupling of an iodothienopyridine (3) with 5-(tributylstannyl)-1-methylimidazole (11). Several cross-coupling methods were evaluated for the conversion of thienopyridine 3 to imidazole-thienopyridine 2, but only two were effective: the Stille coupling and a Negishi cross-coupling of the organozinc reagent derived from 2-(tert-butyldimethylsilyl)-1-methylimidazole and iodothienopyridine (3). The latter procedure worked well on laboratory scale (<50 g), but was capricious upon scale-up. The issues with scale-up of an organostannane reagent are discussed, including control and analysis of organotin levels.