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 [PdCl2(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 mac-rocycles 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 it related product by Ru-catalyzed olefin metathesis delivered yields similar to the Pd-catalyzed mac-rocyclization, but provided a mixture of both double bond isomers. (C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004).