Synthesis of benzo-furan derivatives-I Karanj ketone, karanjin and pongapin

A new method of preparing benzo-furan derivatives using substituted allyl phenols has been worked out. Ozonolysis of the allyl derivatives and subsequent ring closure of the resulting o-hydroxy-acetaldehydes by means of o-phosphoric acid give good yields of karanj ketone, karanjin, pongapin and the corresponding 2-methyl furanochromone. As an alternative route oxidation of the allyl phenol in two stages using performing acid followed by periodic acid has been successfully employed in the synthesis of karanjin.