Efficient Synthesis of 9‐Aminophenanthrenes and Heterocyclic Analogues by Electrocyclization of Biaryl Keteniminium Salts

Abstract

Dedicated to Prof. Janine Cossy in recognition of her important contributions to the discovery of new stereoselective methods and their application to the synthesis of natural productsWe describe herein a high yielding and metal-free methodology to access 9-aminophenanthrene derivatives and heterocyclic analogues starting from biaryl acetamides. The conversion of the substrates to their corresponding keteniminium salts triggers a spontaneous electrocyclization occurring at room temperature within a few minutes. DFT Calculations and competition reactions were carried out to rationalize the observed reactivity and understand the relative kinetics compared to other known reactions involving keteniminium salts.

Novel Synthetic Approach towards Amino‐Substituted Polycyclic Aromatic Hydrocarbons through Electrocyclization of Keteniminium Salts

“…We were able to synthesize the amino-substituted tribenzo[c,I,o]triphenylene 12a/ 12b as a mixture of two diastereomers in one-step Moreover, we propose the extension of PAH structure by the iterative electrocyclizations of keteniminium salts illustrated in Scheme 2,E. The first keteniminium electrocyclization provided the diallylamino-substituted phenanthrene 2a, [6] then this diallylamino group can be converted into the corresponding iodophenanthrene 13 through the palladium catalyzed deprotection followed by Sandmeyer iodination. [40] The iodophenanthrene 13 was transformed into the phenylphenanthrene 14 having a diallylamide residue by cross-coupling reaction.…”

“…Supporting information for this article is available on the WWW under https://doi.org/10.1002/hlca.202300085 Recently, we developed a novel synthetic method accessing various amino-substituted phenanthrenes through a highly reactive keteniminium intermediate. [6] Keteniminium salts are very reactive electrophiles, able to take part in diverse reactions as [2 + 2] cycloadditions, [7 -9] electrocyclizations, [10 -15] Friedel-Crafts, [16,17] hydride shift [18] and others. [19 -22] Herein, we describe the use of multiple 6π-electrocyclizations to efficiently reach amino-substituted PAHs in a single operation (Figure 1).…”

“…Recently, we developed a novel synthetic method accessing various amino‐substituted phenanthrenes through a highly reactive keteniminium intermediate [6] . Keteniminium salts are very reactive electrophiles, able to take part in diverse reactions as [2+2] cycloadditions, [7–9] electrocyclizations, [10–15] Friedel‐Crafts , [16,17] hydride shift [18] and others [19–22] .…”