Synthesis of 2,4‐Furanophanes by Palladium‐Catalyzed Macrocyclization Reactions of 1, n ‐Diallenyl Diketones

The 1, n ‐diallenyl diketones 8a − j were prepared and subjected to reactions with the [PdCl 2 (MeCN) 2 ] catalyst. Upon decreasing the length of the bridge between the allenyl ketone units, first we obtained the ( E ) isomer 10 as the macrocyclic product and then the ( Z ) isomer 11 accompanied by the exocyclic double bond isomer 12 . In all cases, the open‐chained 1, n ‐difuryl alkanes were isolated as side‐products. The analogous preparation and conversion of the diallenyl diketones 19 and 24 , which have even longer bridges and ether‐functionalities, delivered the 20‐ to 52‐membered macrocycles 21a , 21b , 26a , and 26b with only the expected ( E ) configuration of the double bond. The ring closure of a furan derivative, having vinyl groups in its substituents at the 2‐ and 4‐positions, to a related product by Ru‐catalyzed olefin metathesis delivered yields similar to the Pd‐catalyzed macrocyclization, but provided a mixture of both double bond isomers. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)