THE BASE-CATALYZED CYCLIZATION OF ACYLMETHYL ETHERS OF 7-HYDROXYCOUMARINS

We have studied the base-catalyzed cyclization of acylmethyl ethers of 7-hydroxycoumarins which proceeds via lactone ring opening and yields psoralen derivatives. Corresponding cinnamic acid derivatives have be en isolated The cyclization is a highly regioselective reaction, produ cing only linear furocoumarins. According to MNDO calculations, the an ionic sigma-complex formed due to acylmethyl attack to the C-6 positio n of the coumarin turns out to be more stable than that to the C-8 pos ition. A series of new psoralens with phenyl group in the lactone and (or) in the furan ring have been synthesized and characterized By NMR and mass spectra.