Research On Palladium-catalyzed Cyclization And Cleavage Reaction On Basis Of Aromatic Alkynes

The transition-metal-catalyzed cross-coupling reaction continues to be a very importantfield of organic synthesis chemistry. Among the transition metal catalysts, palladiumcomplexes play an important role in organometallic chemistry. Palladium complexes exist inthree easily interconvertible oxidation states, Pd（0）, Pd（II） and Pd（IV）. Furthermore, thereaction conditions can be tuned by varying the ligands, base, oxidant, solvent, temperature,and additives to optimize these oxidation states. On the other hand, Palladium-mediatedorganic transformations continue to be a fascinating area in organic synthesis as well asorganometallic chemistry because most palladium-based methodology proceeds stereo-andregioselectively in excellent yields under relatively mild reaction conditions and tolerates awide variety of functional groups. Molecular oxygen is an abundant and environment benignoxidant. Generally speaking, Pd（II）/O₂catalytic system have higher selectively and undermilder reaction conditions as compare to KMnO₄, OsO₄, RuO₂and O₃. Therefore, theutilization of molecular oxygen as oxidant in palladium catalyzed oxidation of alkenes andalkynes are highly desirable.In this context, we have studied the palladium-catalyzed transformation of alkynes withmolecular oxygen. The details are summarized as following:（1） Palladium-catalyzed cyclization of aromatic alkynes to tetrasubstituted furans.Tetrasubstituted furans represent one of the most prominent classes of five-memberedheterocycles. In chapter2, we developed a novel method for synthesis of tetrasubstitutedfurans from readily available alkynes under mild reaction conditions via the palladiumcatalyzed and Cu（OAc）₂promoted cyclization process. This protocol not only utilized theeasy available starting materials but also have good selectivity（2） Palladium-catalyzed oxidative cleavage of alkynes. The cleavage reaction ofalkynes is one of the most challenging subjects in modern synthetic organic chemistry.Generally, the cleavage of C-C triple bond is achieved by using KMnO₄, alkaline H₂O₂,ozone, OsO₄and RuO₄. In chapter3, we have developed a MeSO₃H promoted andpalladium-catalyzed cleavage reaction with molecular oxygen in which alkyne is split intocarboxylic ester in various alcohols.