Novel Ruthenium-Catalyzed Synthesis of Polycarboxylic Acid Derivatives

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Both aliphatic and aromatic polycarboxylic acid derivatives are highly important intermediates in chemical industry. In this study, we developed the following novel ruthenium-catalyzed syntheses of polycarboxilic acid derivatives involving cross-coupling and cycloaddition reactions. First, pyranopyrandiones were prepared by a novel ruthenium-catalyzed carbonylative dimerization of cyclopropenones via C-C bond cleavage. For example, treatment of dipropylcyclopropenone with a catalytic amount of Ru_3(CO)_<12> and NEt_3 in THF under 15 atm of carbon monoxide at 140℃ for 20 h gave a novel functional monomer, 3,4,7,8-tetrapropylpyrano[6,5-e]pyran-2,6-dione, in an isolated yield of 81%. Unsymmetrically substituted pyranopyrandiones were also obtained by ruthenium-catalyzed carbonylative coupling of cyclopropenones with alkynes under similar reaction conditions. All pyranopyrandiones prepared in this study are new compounds, which are quite attractive as novel functional monomers due to their … More characteristic physical and chemical properties. Then, a catalyst system consisting, of Cp*RuCl(cod)/PPh_3 [Cp* = pentamethylcyclopentadienyl, cod 1,5-cyclooctadiene] for the novel cross-benzannulation of 2 equip of dialkyl acetylenedicarboxylate with an allylic compound has been developed. As an example, the reaction of dimethyl acetylenedicarboxylate with allyl alcohol in the presence of 4 mol % Cp*RuCl(cod) and PPh_3 under reflux in toluene for 5 h gave tetramethyl 5-methyl-1,2,3,4-benzenetetracarboxylate in an isolated yield of 84%. Furthermore, a highly chemoselective intermolecular [2 + 2 + 2] cycloaddition of 2 eqiv of terminal alkynes with dimethyl acetylenedicarboxylate, which enables the straightforward synthesis of dialkylated o-phthalates, was successfully accomplished using a ruthenium catalyst, Cp*RuCl(cod). The co-cyclotrimerization of alkynes and acetylenedicarboxylates usually affords 1:2 adducts (1,2,3,4-benzenetetracarboxylates), however, in the present reaction 2:1 adducts (o-phthalates) are the major products unprecedentedly. Recently, we have also reported the novel zerovalent ruthenium complex Ru(η^6-cot)(dmfm)_2, which showed high catalytic activity in a unique dimerization of 2,5-norbornadiene to novel half-cage compounds, PCTD [pentacyclo[6.6.0.0^<2,6>.0^<3,13>.0^<10,14>]tetradeca-4,11-diene]. During our further investigation of the reactivity of this complex, we found that the reaction with p-quinones gave Ru(η^6-cot)(p-quinone) complexes, while the reaction with arenes gave novel (η^6-arene)Ru(dmfm)_2 complex. All reactionsproceeded via the direct ligand exchange reactions of cot and/or dmfm in Ru(η^6-cot)(dmfm)_2, and the new complexes prepa-red here can be expected as efficient catalysts for the synthesis of aliphatic and aromatic polycarboxylic acid derivatives. Less