Tandem Ring-Contraction/Regioselective C–H Iodination Reaction of Pyridinium Salts

Abstract

A facile route for direct access to the 4-iodopyrrole-2-carbaldehydes from pyridinium salts has been successfully developed, which undergoes cascade pyrrole-2-carbaldehydes construction/selective C4 position iodination process. Using Na 2 S 2 O 8 as an oxidant and readily available sodium iodide as an iodine source, a variety of 4-iodopyrrole-2-carbaldehydes were obtained in good to excellent yields. Atom-and stepeconomy, good functional group tolerance, high regioselectivity, as well as mild conditions entail this transformation an alternative strategy for enriching pyrroles library.

Photochemical Skeletal Editing of Pyridines to Bicyclic Pyrazolines and Pyrazoles

“…Pyridine skeletal editing transformations can be categorized into two strategies: ring expansion and ring contraction (Figure D). Typically, the nucleophilicity of the nitrogen atom of pyridines is harnessed to prepare cationic pyridinium salts. − Pyridine expansion via N-functionalized pyridinium salt (imidopyridine ylide) has been widely employed in synthetic methodologies. − Additionally, ring contractions via carbon deletion under light or electricity have been documented, yielding pyrroles or pyrazolines as exclusive products. − …”

A DFT study of NHC-catalyzed reactions of [3+3] annulations of 2-bromoenals and thioamides: mechanisms and regio- and stereoselectivities

“…In particular, NHC-catalyzed annulations provide a powerful method for carbocycle and heterocycle syntheses. This has led to the synthesis of various cyclic molecules through NHCcatalyzed [2+2], [35][36][37] [3+n] (n = 2, 3, 4) 38-41 and [4+n] (n = 1, 2) [42][43][44] annulations (Scheme 2).…”