Bardhan-Sengupta phenanthrene synthesis

The Bardhan-Sengupta Phenanthrene Synthesis uses P2Os in place of H2SO . 

Another Friedel-Crafts route to phenanthrenes is the Bardhan-Sengupta phenanthrene synthesis. When phenethylcyclohexanol 222 was cyclized with phosphorus pentoxide at 140°C, the product was 223. Aromatization was accomplished by heating with selenium to give the phenanthrene derivative 224 (1-methyl-7-isopropylphenanthrene, otherwise known as retene). An improvement in the reaction used hydrogen fluoride (HF) to induce cyclization.l ... 

Much like the work conducted by the Bogert and Cook groups, the Bardhan-Sengupta synthesis of phenanthrenes helped lead to the determination of the carbon framework for steroids and was used to prepare terpene-type natural products. 

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