Research On The Synthesis Of Carbocycles Mediated By Transition Metal

The synthesis of carbocycles is industrially valuable and theoretically important. For the synthesis of carbocycles, transition metal-mediated approaches toward the carbocycles are the most attractive undoubtedly. Principally speaking, transition metal-mediated approaches toward the carbocycle can be divided into four kinds: (a) intramolecular cyclization (b) cycloaddition (c) multi-component cyclization (cyclization via tandem reactions) (d) cyclization of dianions. The multicomponent cyclization-mediated by transition metal represents a higher efficient method to complex rings with poly-functional groups in one pot via fewer steps. The cyclization of dianions mediated by transition metal is well developing these years because of the simple strategy, high efficiency, the straightforward introduction of multiple carbon units and the ability of constructing special cyclic compounds.The work in this paper was mainly focused on the study of cyclization of dianions mediated by transition metals and during the course, several multi-component cyclization reactions were also observed by way of parenthesis. Several novel cyclization reactions were developed from dianions containing zirconium: (1) the reactions of zirconacycles with oxalyl chloride. The problem of unmatching reactivity in the 1,1-cycloaddition of zirconacycle with oxalyl chloride to form five-membered cyclopentanones was solved and the mechanism of the reaction was elucidated and testified as well. (2) the reaction of zirconacyclopentadienes with quinones. The quinones with high oxidative potential only worked as the oxidant converting the zirconacyclopentadiens into cyclobutadienes while the quinones also underwent a cycloaddition with zirconacyclopentadienes to afford high quinones when its oxidative potential decreased. (3) The zirconacyclopentadines reacted with acrylates to afford Dewar-benzene derivatives. The reaction with bromo acrylates or bromo cinnamaldehyde afforded benzene derivatives instead. (4) multi-component cyclization of bromo acrylates was studied. Many rings could be prepared from bromo acrylate in one pot initiated by various metal reagents or catalysts.In the cyclization reactions of dianions with proper substrate, the key was to tune the reactivity of dianions and the substrate. The proper tuning would not only promote the reaction to proceed in mild condition and avoid the side reaction, but also change the process to result in a different cyclization. The problem of regio-selectivity in the reaction of dianions with multi-electrophiles was also represented and the coordinated effect between the transition metal with the substrate was the reliable key factor for the regio-selectivity and stereo-selectivity.