DIELS-ALDER REACTIONS OF 1,3-DIPHENYLISOBENZOFURAN WITH FERROCENYL-TRICARBONYLCHROMIUM AND (ETA(6)-PHENYL)TRICARBONYLCHROMIUM ANALOGS OF CHALCONE AS WELL AS SOME OTHER DIENOPHILES

The Diels-Alder reactions of 1,3-diphenylisobenzofuran with acryloylfe rrocene (1), 4-ferrocenyl-3-buten-2-one (2), cinnamoylferrocene (3), 3 -ferrocenyl-1-phenyl-2-propenone (4), chalcone (5), 6)-phenyl)tricarbo nylchromio)-3-phenyl-2-propenone (6), -3-((eta(6)-phenyl)tricarbonylch romio)-2-propenone (7), and (2-nitrovinyl)ferrocene (8) were examined under various conditions. The best results were achieved using SiO2 an d a very acidic montmorillonite clay, KSF, as the catalyst, and the re actions were carried out without solvent. Reasonable to good yields of the Diels-Alder (D-A) products were isolated in most cases. X-ray str uctural studies showed that the adducts 13b and 13h, derived from the (E)-alkenes 2 and 8, have exo-acetyl or -nitro substituents and endo-f errocenyl groups with respect to the bridging oxygen atom of the 7-oxa bicycloheptane ring system. The product 13a from the monosubstituted e none 1 also has an exo-acyl (ferrocenylcarbonyl) group. Aluminum chlor ide was found to be a good catalyst for the reactions of 1,3-diphenyli sobenzofuran with push-pull alkenes like 1, 2, 4, and 8. The unexpecte d products were derived from cl-ferrocenyl carbocation attack on the d iene, followed by electrophilic 2-substitution of the cyclopentadienyl ion ring, rather than D-A addition. The X-ray structure of the 8-oxab icyclooctane 12b, derived from 4, revealed an exo-ferroceno group and endo-phenacyl substituent.