INTRAMOLECULAR DIELS-ALDER REACTIONS OF VINYLFURANS LEADING TO FURANODECALINS

Thermolysis of the (2E,8Z)-9-(2-furyl)nonadienoate 25 at 290-degrees-C leads to an essentially quantitative yield of a single furanodecalin 26, whereas the corresponding (2E,8E)-isomer 34 undergoes a non-stereoselective cyclisation leading to the furanodecalins 26 and 35. (Z)-Alkenoate functions undergo partial isomerisation prior to cyclisation and so lead to mixtures of isomers. Alkyl groups can be incorporated around the reaction sites, but this can result in overwhelming competition from side reactions. The corresponding 3-furyl analogues 56 and 59 display very similar reactivities.