5-Unsubstituted-2-Pyrrolecarboxaldehydes for Porphyrin Synthesis and the Cyanovinyl Protecting Group
Paine, J.B. III and David Dolphin
J. Org. Chem.
(Cyanovinyl)pyrroles I (R = Me, R1 = Et, octyl; R = Et, R1 = Me) derived from the Knoevenagel condensation of benzyl 5-formyl-2-pyrrolecarboxylates with NCCH2CO2Me were employed in a facile sequence of 4 steps to produce, regioselectively, 2-pyrrolecarboxaldehydes II, important intermediates for porphyrin synthesis. Each step proceeded in 90-95% yield, making II available smoothly from benzyl 5-methyl-2-pyrrolecarboxylates in 7 steps, with an overall yield of 66-72%.