Activated pyrroles from pyridazines: nitrogen extrusion by electroreduction

Functionalized 2,5‐Dipyridinylpyrroles by Electrochemical Reduction of 3,6‐Dipyridinylpyridazine Precursors

“…These observations can be explained by a poor stability in acidic solution of the first-formed 3,6-dipyridin-2-yl-1,2-dihydropyridazine intermediate and its rather rapid disproportionation into the starting pyridazine and the pyrrole (Scheme 3, Path b), which thus accounts for the increase in the current intensities of peaks I and III, respectively. [8,9] Scheme 3. General transformation pathway of pyridazines into pyrroles.…”

“…Recently, we showed that electrochemical transformations of 3,6-bis(methoxycarbonyl)pyridazines 1 in an acidic [ medium proceeds by a four-electron reduction process to give the corresponding 2,5-bis(methoxycarbonyl)pyrroles 5 according to the mechanism shown in Scheme 1. [8,9] Scheme 1. Mechanism for the electrochemical reduction of bis-(methoxycarbonyl)pyridazines.…”

Synthesis of Polyhydroxylated Pyrano‐Pyrrole Derivatives from Carbohydrate Precursors

“…As a result of our interest in the synthesis of pyrrole heterocycles by ring contraction of pyridazine precursors using Boger's chemical strategy [16] or an alternative electrosynthesis methodology developed in our laboratory, [17][18][19][20] we have developed a synthesis of novel linear (pyrone type A) and cyclic polyhydroxylated pyrrolo-pyrone derivatives (pyrone types B and C) ( Figure 3) structurally analogous to boronolide (3a), altholactone (4), indololactone (10), or bergenin (11). Recently, we validated a general efficient synthetic approach to pyrrolo-pyrones A bearing a polyol side-chain.…”

Unravelling the Reaction Mechanism of the Reductive Ring Contraction of 1,2-Pyridazines

“…Generation of intermediates 19/23, however, is also very exergonic, and it is therefore very likely that the final protonation occurs on any of these intermediates, leading to the production of a mixture of intermediates 24-27 ( Table 1 Since NH 2 is not a good leaving group, the transfer of a proton to this group is now required. This 14 Finally, the 1,4-dihydropyridazine intermediate (4/6 in our scheme) found in electrochemical investigations 13,14 and isolated in the course of the total synthesis of ent-(-) roseophilin 9 seems to be part of an unproductive pathway involving (at the four-electron-reduced stage)…”