Synthesis of 1,3-azaphospholo[1,5-f]phenanthridines through 1,5-electrocyclization

GRAPHICAL ABSTRACT

ABSTRACT

A new class of annelated azaphospholes, namely 1,3-azaphospholo[1,5-f]phenanthridines, has been synthesized from the reaction of 5-(alkoxycarbonylmethyl/phenacyl)phenanthridinium bromides with phosphorus trichloride in the presence of triethylamine at room temperature. The reaction involves intramolecular 1,5-electrocyclization of the initially generated bis(phenanthridiniumylidyl)phosphenium chloride accompanied by 1,2-elimination to afford the title compounds in 15–64% yields. All the compounds so obtained are new and have been characterized by ³¹P-, ¹H-, and ¹³C NMR studies. The C˭P functionality in these compounds is reactive and undergoes the Diels–Alder reaction with dimethylbutadiene with concomitant oxidation with sulfur at the phosphorus atom.

KEYWORDS:

• Annelated azaphospholes
• 1,5-electrocyclization
• 1,3-azaphospholo[1,5-f]phenanthridines
• Diels–Alder reaction

Acknowledgments

We thank the authorities of the IIS University, Jaipur (India) for providing facilities.

Funding

Financial support from the University Grants Commission, New Delhi is gratefully acknowledged.