Starting from Y-lactone intermediates, a novel method for the synthesis of the 5,6-dihydro-4H-cyclopenta[blfuran system has been developed which was utilized to prepare furanoprostacyclin derivatives. Because of the inherent instability of prostacyclin towards hydrolytic conditions 2 and its rapid decomposition into 6-ketoprostaglandin Fla3, we have been engaged in a program to develop syntheses of stable prostacyclin analogs which would be suitable for treating hypertension and/or occlusive circulatory disorders4. An obvious structural modification which would confer stability to the prostacyclin structure would be the modification of the enol ether moiety into a fully-aromatic furan derivative i_ Nicolaou5 has described the synthesis of the "first" pyridazaprostacyclin 2, by treatment of the 6,9-diketone 2 drogenation with platinum dioxide. Our attempts to cyclize conditions6 furnished, however, only the PGAl derivative $ aromatic prostacyclin analog, 6,9with hydrazine and subsequent dehythe diketones 2 or f under acidic and no trace of the desired furan. It therefore became necessary to develop a new approach for the preparation of strained, polyfunctionalized cyclopenta[b]furan derivatives7 starting from Y-lactone intermediates.