Study On The Transformations Of Cyclopropenes With Transition-Metal Catalysis

Cyclopropenes are the smallest unsaturated carbocyclic but readily accessible compounds with high ring strain energy (54.1kcal/mol), which resulting in the high activity of cyclopropenes in reactions. Cyclopropenes have been a hot research topic for many years including synthesis and transformations, and a series of interesting and significant cyclopropene chemistry have been demonstrated. Especially when transition-metal-catalysts were introduced into cyclopropene chemistry, a number of unprecedented transformations through addition reactions, cycloadditions, and ring-opening reactions have been developed. In this thesis, we developed a new and efficient tandem metal relay catalysis (TMRC) method to transform cyclopropenes to multisubstituted furans. There are two parts in this thesis.Part Ⅰ, Transformation of cyclopropene to multisubstituted furans by Cu/Pd relay catalysis.Chapter I Isomerization/oxidative Heck reaction cascade sequence of cyclopropenes with copper/palladium relay catalysis was studied. Firstly, copper acetate catalyst reacts with cyclopropene, which results in the ring-opening isomerization of the substrates, and the subsequent transmetalation with Pd(II) to generate the key furanyl palladium intermediate, which underwent the oxidative Heck reaction with alkene to afford the products. In this part, we developed a convenient and efficient method for the synthesis of substituted furan derivatives from cyclopropenes under mild conditions.Chapter Ⅱ, we extended the methodology of the isomerization/functionalization cascade sequence of cyclopropenes with copper/palladium relay catalysis to oxidative carbonylation reaction. When we exposed our system into the CO atmosphere in the presence of alcohols, the tetrasubstituted furan carboxylates were successfully afforded, which proved the existence of the key furanyl palladium intermediate. This reaction also provides a general modular synthesis of all substituted furan derivatives from easily available materials. The most important feature of this methodology is the mild transmetallation relay strategy to form the key C-Pd bond which is greatly different from the general C-H activation mode, which normally require very harsh reaction conditions.Chapter III, Organic optoelectronic materials have drawn the attentions for decades due to their many advantages, such as light-weight, low-cost, simple-process, high luminous efficiency, wide luminous color and so on. In this part, it was found that the key furanyl palladium intermediate could afford bifuran products under a higher temperature (80℃). Optophysics data shows the obtained bifuran products very good luminous property, with a high fluorescence efficiency ((?)=0.97), the bifuran compounds show very promising optoelectronic properties as blue emissive materials used as OLEDs.In chapter IV, we successfully developed a new and efficient method for the synthesis of highly functionalized tetrasubstituted alkenes. With a Cu/Pd-catalyzed isomerization/insertion/oxidative coupling cascade reaction of cyclopropenes with internal alkynes, a wide variety of cis-tetrasubstituted olefins were synthesized in good yields as single stereoisomers. The photophysical properties of these novel tetraarylethenes were fully studied and proved to be good AIE luminogens. Detailed experimental studies and theoretical calculation were carried out to study the reaction mechanism and it was discovered that the actual catalysts of this reaction were Cu(I) and Pd(II), and the key Cu/Pd transmetallation steps all thermodynamically feasible processes.In part II, we studied the direct functionalization of cyclopropenes with transition metal catalysis:In chapter V, we investigated the functionalization of cyclopropene with single copper catalysis. We found that cyclopropene could react with bis(pinacolato)diboron and allyl bromide with the three-membered carbocycle structure reserved in the presence of CuCl. This reaction underwent boronation/allylation sequence of the unsaturated double bond of cyclopropenes. By using a chiral ligand together with CuCl, moderate enatioselectivity was obtained. With this reaction, a new method for the systhesis of boron-substituted cyclopropanes was successfully achieved.