Regiocontrolled Synthesis of Pyrrole-2-carboxaldehydes and 3-Pyrrolin-2-ones from Pyrrole Weinreb Amides.

A regiocontrolled synthesis of 3,4-disubstituted pyrrole-2-carboxaldehydes was completed in two steps from acyclic starting materials. A Barton−Zard pyrrole synthesis between N-methoxy-N-methyl-2-isocyanoacetamide and α-nitroalkenes or β-nitroacetates provided N-methoxy-N-methyl pyrrole-2-carboxamides (pyrrole Weinreb amides), which were converted into the corresponding pyrrole-2-carboxaldehydes by treatment with lithium aluminum hydride. A regioselective oxidation of the pyrrole-2-carboxaldehydes gave the corresponding 3,4-disubstituted 3-pyrrolin-2-ones.