Survey of new synthetic paths to substituted and condensed furocoumarins, perspective compounds for photochemotherapy is given. These furocoumarin syntheses are based on the use of dihydrofurocoumarinones as convenient synthons. Both dihydrofuro [2,3-h]coumarin-9-ones and dihydrofuro[2,3-g]coumarin-6-ones became available via the unusual Fries rearrangement of 7-hydroxycoumarin chloroacetates. Substitution and keto-enol reactions of dihydrofurocoumarinones followed by aromatization of

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... anone moiety are key steps of substituted and condensed furo[2,3-h]-and furo[2,3-g]coumarins synthesis. We have already characterized in our previous papers many of the compounds listed in the survey. The structures of new compounds are proved by mass spectral, 1H NMR spectral and elemental analysis data Dihydrofuro[2,3-h]coumarin-9-ones 2a, b undergo keto-enol tautomeric transformations (Scheme 3). O CH 3 O O O 2b, keto O CH 3 O O OH 2b, enol Scheme 3 Analyzing 4-methyldihydrofuro[2,3-h]coumarin-9-one 2b reactivity, we have studied its equilibrium transformations in more detail. Electron absorption spectra of 2b in CCl 4 -MeOH mixtures have been recorded and an isosbestic point has been registered. Positions of the longestwavelength absorption bands in the UV spectra have been found at 330 nm in methanol and at 285 nm in CCl 4 . We have assigned the band at 330 nm to the enol form absorption, since its PPP CI-calculated position is located at 328 nm. Both semiempirical and nonempirical quantum chemical calculations showed the keto form to be a predominant one. The difference between formation energies of keto and enol forms has been found equal to -10.57 and -8.82 kcal/mol by AM1 and PM3 calculations respectively. General Papers ARKIVOC 2000 (iv) 523-562 Keto-enol tautomeric transformation of 4-methyldihydrofuro[2,3-h]coumarin-9-one 2b turned to be a key way of many its reactions. We have carried out chlorination and bromination of the General Papers ARKIVOC 2000 (iv) 523-562 Synthesis of 8-formyl-4-methyldihydrofuro[2,3-h]coumarin-9-one 7g has been carried out by Vilsmeier-Haack reaction with isolation of dimethylamine 9 as an intermediate product instead of oxonium chloride 10. The following Scheme can be suggested for explanation of the results (Scheme 4). General Papers ARKIVOC 2000 (iv) 523-562