Synthesis of benzo[a]pyren-1-ol

Abstract

Benzo[a]pyren-1-ol has been synthesized from phenanthrene-9-carbaldehyde in six steps. An initial Knoevenagel reaction gives trans-β-phenanthren-9-ylacrylic acid, which is reduced catalytically to β-(9,10-dihydrophenanthren-9-yl)propionic acid. Cyclization of the propionic acid by use of anhydrous hydrogen fluoride gives 5,6,6a,7-tetrahydrobenz[de]anthracen-4-one, which on condensation with methyl succinate followed by decarboxylation yields β-(7H-benz[de]anthracen-4-yl)propionic acid. It is suggested that the benzanthracenylpropionic acid arises via an acid-catalysed disproportionation during the decarboxylation of (5,6,6a,7-tetrahydro-4H-benz[de]anthracen-4-ylidene)succinic acid. Benzo[a]pyren-1-ol is obtained from cyclization of the benzathracenylpropionic acid with anhydrous hydrogen fluoride; dehydrogenation of the expected 3,6-dihydrobenzo[a]pyren-1(2H)-one to the phenol occurs spontaneously during this step.