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SummaryPalladium-catalyzed double carbomethoxylation of the Diels-Alder adduct of furan and maleic anhydride yielded the methyl all-exo-7-oxanorbornane-2,3,5,6-tetracarboxylate (7) which was transformed in three steps into 2,3,5,6-tetramethylidene-7-oxanorbornane (l), a useful synthon. Six isomeric methyl 7-oxanorbornane-2,3,5,6-tetracarboxylates (7-12) have been isolated and their 'H-and 13C-NMR. data are compared.

SummaryPreparation of the title compounds 11, 12 and 13 is described. Preliminary kinetic results indicate that the hydroxyl substituents in 11 and 12 have a very small retardation effect on the Diels-Alder reactivity of 2,3-dimethylidene-norbornane. The keto group in 13 exerts a larger retardation effect, although it is much smaller than the retardation effect introduced by an exo-5,6-epoxide ring in 2,3-dimethylidenenorbornane.Introduction. -Chemical and spectroscopic properties of the s-cis-butadiene chromophore in 2,3-dimethylidene-norbornane 1 can be modified without direct substitution of the diene moiety. Substitution of an ethereal bridge for the HzC(7) bridge (2, 4, 6) and/or introduction of a double bond (5, 6) or of an exo-epoxide ring (3, 4) for the HzC(5)-HzC(6) bridge cause a decrease in the rates of Diels-Alder cycloaddition with strong dienophiles [I]. A priori, these observations are explicable by: (a) geometry changes of the diene moiety in 1-6 due to modification of the ring strain of the bicyclic skeleton or by removal of gauche interactions; (b) changes in steric hindrance due to modified gauche interactions between the cycloaddends in the transition state ; (c) variations in the electrostatic interactions between the cycloaddends themselves, between the solvent and the cycloaddends and between the solvent and the transition states; (d) differences in electronic properties of the s-cisbutadiene group (energies and shapes of the frontier and extra-frontier MO's) in 1-6 due to through-space and/or through bond interactions [2] between the non-conjugated chromophores.The lack of correlation between ring strain of the bicyclic skeleton and the observed reactivity differences and the non-observation of bridgehead methyl sub-

(18), respectively, without loss of the olefin configuration. Ethylene tetracarbonitrile (TCE) and N-phenyltriazolinedione (NPTAD) added to these new exocyclic dienes and tetraenes preferentially onto their exo-face. The same face selectivity was observed for the cycloadditions of TCE to the (Z)-and (E)-chlorodienes 9 and 10, thus realizing a case where the kinetic stereoselectivity of the additions is proven not to be governed by the stability of the adducts. The exo-face selectivity of the Diels-Alder additions of dienes grafted onto 7-oxabicyclo [2.2. llheptanes contrasts with the endo-face selectivity reported for a large number of cycloadditions of dienes grafted onto bicyclo [2.2. llheptane skeletons.