Synthesis of Natural Products Based on the Allene Intramolecuar Cycloaddition Stategy

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The intramoleculat cycloadditions of allenes constitute the versatile methods for the stepreocontrolled synthesis of variously functionalized polycylic compounds. In paticular Diels-Alder reactions fully enjoyed the merits of the uique structure of allenes and proceed with extraordinary ease. On the basis of this allene intramolecular cycloaddition strategr, we have developed wvatious general systheric methods as follows.1. New polycycile Lactone Synthesis.We habe found that the allenyl ether undergoes the intramolecular Diels-Alder reaction with extraordinarty ease due to the favorable geomtry. The adducts thus obtained are easily converted into the correponing polycyclic lactones by bydratio-oxidation procedure. This method was successfully utilized in the synthesis of vasrious polycyclic lactones and spplied to the total syntersis of noreqsuiterpene lactone, (+-)platyphyllide.2. Furan Ring Transfer (FRT) Reaction.We habe developed a novel ring rtransfer reaction of furans to fused furans by virstue of a facile intramolecular Diels-Alder reaction of allenyl furfuryl ether and base-catalyzed ring opening of the resulting adduct. This method also opened the way to a new generation of syntherically versatial isobenzofurans.3. New indole Synthesis.We have developed a new versatile indole synthesis based on the intramolecular Diels-Alder of allenic dienamide and dehydrogenation of the adduct. By this method a variety of alkylated indoles were synthesized. A new class of pyrrolophenathridone alkalid, Hippadine, was also synthsized using this new methodology.