Bardhan-Sengupta phenanthrene

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. 

In 1932, Bardhan and Sengupta reported the use of P2O5 to cyclize hydroxy ester 6 that, upon treatment of the crude product with Se metal and heat (300-320 °C), provided 8 presumably through an intermediate like compound 7 (R = H or Et). In an additional publication, the authors provided more experimental detail and examples on the formation of substituted phenanthrenes. ... 

Another attempt to synthesize steroids was carried out with the Grignard reaction of the 2-methylcyclohexanone (67) with the bromide (68) as a model example. On cyclization, the tertiary alcohol (72) so obtained formed compound (71) with the eye lope ntanophenanthrene skeleton, which apparently had the cis-linkage of rings B and A [55]. This synthetic route is an extension to eye lope ntanophenanthrene of Bardhan and Sengupta s method of obtaining phenanthrene derivatives [422]. 

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