Base‐Promoted Aerobic Oxidation/Homolytic Aromatic Substitution Cascade toward the Synthesis of Phenanthridines

Abstract

The current protocol represents a transition metal-free synthesis of polysubstituted phenanthridines from abundant starting materials like benzhydrol and 2-iodoaniline derivatives. The reaction involves sequential oxidation of alcohol and direct condensation reaction with the amine resulting in a CÀ N bond formation followed by a radical CÀ C coupling in a cascade sequence. The used base potassium tert-butoxide plays a dual role in dehydrogenation and homolytic aromatic substitution reaction. Using this methodology, twenty substituted phenanthridine derivatives were synthesized with up to 85% isolated yield.

Alcohols as Fluoroalkyl Synthons: Ni‐catalyzed Dehydrogenative Approach to Access Polyfluoroalkyl Bis‐indoles

“…[16] Our ongoing research is extensively focused on the exploration of easily accessible alcohols for the construction andf unctionalizationof important heterocycles using an AD approach. [17] Along this line, we realized that polyfluorinated alcohols are cheap, stable and its dehydrogenatedc arbonyl derivative which is reactivec an be utilizedf or the incorporationo f fluoroalkyl groups. But majori nherento bstacles that exist in the dehydrogenation of fluoroalcohols are:a )high OÀHa nd CÀHb ond strengths,b )immensei nductive effect of fluorine atomse levatet he destabilization during b-hydride elimination and c) rapid hydrogenation process make the aldehyde unstable (Scheme 1).…”

Photocatalyzed syntheses of phenanthrenes and their aza-analogues. A review

“…Most of the protocols illustrated herein, however, involved the use of rather expensive transition-metalbased (e.g., on Ru or Ir) photocatalysts, that still represents an issue in terms of sustainability. In this context, the use of photoorgano-catalysts [24] is a promising opportunity on the route towards metal-free protocols for the synthesis of the phenanthrene and phenanthridine cores, a topic of current interest also in related thermal methods [94,95].…”

Recent Trends in the Synthesis and Mechanistic Implications of Phenanthridines

“…Sarkar and group demonstrated an innovative cascade synthetic method of phenanthridine derivatives 391 from ample starting materials like 2-iodoaniline derivatives 390 and benzhydrol 389. [111] This method involved the sequential oxidation of alcohol derivatives and amine mediated direct condensation reaction to generate a CÀ N bond followed by radical CÀ C coupling. Potassium tert-butoxide showed a duplex character in dehydrogenation and a homolytic aromatic substitution reaction.…”