TANDEM THERMAL CLAISEN-COPE REARRANGEMENTS OF COUMARATE DERIVATIVES -TOTAL SYNTHESES OF THE NATURALLY-OCCURRING COUMARINS - SUBEROSIN, DEMETHYLSUBEROSIN, OSTRUTHIN, BALSAMIFERONE AND GRAVELLIFERONE

Thermal Claisen rearrangements of derivatives of 4'-O-methyl and 4'-O- benzyl methyl coumarates 3, prepared from the corresponding umbellifer one derivatives, have been investigated. Simple allyl derivatives rear range predominantly to the vacant ortho-position while prenyl derivati ves undergo a sterically driven tandem para-Claisen rearrangement. Aft er thermal rearrangement, the resulting 2'-hydroxycinnamate esters rea dily relactonise to yield 3-, 6- and 8-allylated coumarin derivatives in synthetically useful yields.