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The ruthenium catalyzed dimerization of oxanorbornadiene dicarboxylates was studied. The effects of the ester moiety and the addition of a C1 substituent to the bicyclic alkene on the reaction were explored, and moderate yields and excellent regioselectivities were obtained.

The synthesis of 2-substituted furans via palladium-and iron-catalyzed coupling utilizing 2-bromofuran is described. Whereas palladium-catalyzed Suzuki coupling effectively provided the corresponding aryl furans, little or no product was obtained by palladium-catalyzed coupling with various alkyl nucleophiles. Ironcatalyzed coupling proved effective for the synthesis of primary and secondary alkyl furans in modest yields and aryl furans in low yields.Oxabicyclic alkenes are valuable synthetic intermediates because they can serve as a general template to create highly substituted ring systems. 1 For instance, asymmetric ring opening of these alkenes allows the formation of several stereocenters in a single step. 2 We have recently investigated different modes of transition-metal-catalyzed reactions of oxabenzonorbornadiene (1), and found that, depending on the reaction conditions, several products 2-7 could be obtained (Scheme 1).For example, when 7-oxabenzonorbornadiene (1) is treated with an alkyne in the presence of the ruthenium catalyst, [Cp*Ru(cod)Cl], a [2+2] cycloaddition is observed and cyclobutene cycloadduct 2 is formed. 3 When 1 is treated with the secondary propargylic alcohol 8 in the presence of the neutral Ru catalyst, [Cp*Ru(cod)Cl], in methanol or using a cationic Ru catalyst (e.g., [CpRu(MeCN) 3 ]PF 6 ), isochromene 3 is formed. 4 On the other hand, if the same reaction between 1 and the secondary propargylic alcohol 8 is carried out with [Cp*Ru(cod)Cl] in tetrahydrofuran (THF), cyclopropane 4 is produced. 5 More recently, we have observed that in the absence of an alkyne, [Cp*Ru(cod)Cl] catalyzes the isomerization of 1 to the corresponding naphthalene oxide 5 or naphthol 6. 6 We have also reported that asymmetric cationic rhodium(I)-catalyzed cyclodimerization of 1 produces dimers 7 in excellent enantioselectivity (up to 99% ee). 7Because oxabenzonorbornadiene (1) is symmetrical, no regiochemical information could be gained from the above studies. To explore the regioselectivity of the above Scheme 1 Transition-metal-catalyzed reactions of oxabenzonorbornadiene (1)