Nucleophilic displacements of N‐aryl and heteroaryl groups. Part 8 . Intermolecular reactions of N‐aryl‐pyridinium, ‐quinolinium, and ‐acridinium salts with nucleophiles

Abstract

N‐Aryl‐mono‐, ‐tri‐ and ‐pentacyclic pyridinium cations react with S‐ and C‐nucleophiles to give: (i) simple addition of hydride at the α‐ring position, (ii) nucleophilic addition of thiophenoxide at the γ‐ring position, (iii) deprotonation at the 6‐position of a 5,6‐dihydroquinolinium ring followed by prototropic shift to give a 1,2‐dihydroquinoline derivative, (iv) ring contraction of a pyridine to a pyrrole ring, and (v) nucleophilic displacement of the N‐aryl group.

Radical C−N Borylation of Aromatic Amines Enabled by a Pyrylium Reagent

“…Gratifyingly, when the solvent was replaced by the optimal i Pr 2 NC(O)Me, formation of by‐product 59 was suppressed (<5 %), and excellent yields of 5 were obtained (82 %, Table , entry 1). As suggested by Katritzky's report, 59 possibly resulted from HAT from solvent molecules…”

“…Yet, methods which capitalizeo np yridinium salts to generate aryl radicals through SET are largely underdeveloped. ( Figure 1B,b ottom), [12] mainly due to the disfavored thermodynamics for the aryl radicalf ormation. Althoughe xamples of this approachh ave been reported in the past (3 exam- ples), [12] pyrolysis of the reagents is required (ca.…”

“…( Figure 1B,b ottom), [12] mainly due to the disfavored thermodynamics for the aryl radicalf ormation. Althoughe xamples of this approachh ave been reported in the past (3 exam- ples), [12] pyrolysis of the reagents is required (ca. 200 8C), obtaining low yields for very specific substrates, thus relegating these approaches to proof of concept examples with limited synthetic applicability.B ased on our recent interest on pyrylium reagents, [13] we set out to explore this approachinthe context of radicalb orylations using diboron reagents, as they have been shown to be excellent radical acceptors.…”