Studies of palladium-catalyzed coupling reactions for preparation of hindered 3-arylpyrroles relevant to (-)-rhazinilam and its analogues

Suzuki cross-coupling reactions of 3-pyrroleboronic acid derivatives with haloaromatics and the reverse process i.e., the coupling of 3-iodo(bromo)pyrroles with arylboronic acids have been investigated as a potential key step in the synthesis of (-)-rhazinilam and analogues. It was found that 3-iodo-2-formyl-1-tosylpyrroles efficiently coupled with a variety of arylboronic acids in the presence of PdCl2(dppf) as catalyst. This catalytic system is compatible with a broad spectrum of arylboronic acids - electron-rich, electron-poor, hindered, heterocyclic - which easily coupled with the pyrrole substrate.