Novel Carbon-carbon Bond Formation Via Palladium-catalyzed Cross-coupling Reactions Involving Carboxyl (ester) Or Trifluoromethyl

In this thesis, the novel palladium-catalyzed decarboxylative cross-coupling reactions of2-picolinic acid with aryl-and heteroaryl-bromides including benzenes, naphthalenes, pyridinesand quinolines for C-C bond formation has been successfully achieved. A series of tert-butylesters (Ester tert-butoxide) was synthesised via the palladium-catalyzed alkoxycarbonylreactions of boronic acid or boronic acid pinacol esters with di-tert-butyl dicarbonate. A novelmethod has been developed for the preparation of2-trifluoromethyl pyridine and derivative fromthe reaction of pyridine nitrogen oxides with TMS-CF3under mild reaction conditions.1. Arylation of2-Substituted pyridines via Pd-Catalyzed Decarboxylative Cross-CouplingReactions of2-Picolinic acidA novel synthetic route to2-aryl-and heteroaryl-pyridines was discovered and developedvia the palladium-catalyzed decarboxylative cross-coupling reactions of2-picolinic acid witharyl-and heteroaryl-bromides using5mol%PdCl2as catalyst,6mol%BINAP as ligand,K2CO3as base, DMA as solvent. In addition, a series of substituted2-aryl-and heteroaryl-pyridines compounds including benzenes, naphthalenes, pyridines and quinolines were suitablefor this reaction (Scheme1).Scheme1Decarboylative cross-coupling reactions of2-Picolinic acid2. Preparation of tert-Butyl Esters via Pd-catalyzed tert-Butoxycarbonylation ofAryl(hetero) Boronic Acid DerivativesA novel one-step route to aryl (heteroaryl) tert-butyl esters was developed via thepalladium-catalyzed cross-coupling reactions of boronic acid or boronic acid pinacol esters with di-tert-butyl dicarbonate. The cross-coupling reactions can produce up to94%yields desiredproducts by using palladium acetate and triphenylphosphine as catalyst system, dioxane as asolvent. In the reaction, cheaper, greener and non-toxic di-tert-butyl dicarbonate has been usedcompared to traditional tert-butyloxycarbonylation method. Moreover, a wide range of substratesincluding benzenes, pyridines and quinolines boronic acids or boronic acid pinacol esters can fitthis system as well.(Scheme2).Scheme2Preparation of tert-butyl esters via Pd-catalyzed tert-butoxycarbonylation3. Ag Promoted Trifluoromethylation of Pyridine Nitrogen Oxides via ?-H of PyridineNitrogen Oxides ActivationA novel method has been developed for the preparation of2-trifluoromethyl pyridinederivatives from the reaction of pyridine nitrogen oxides with TMS-CF3under mild conditions. Itis worthy to note that the reaction could be carried on in the presence of F-resouce and Ag+. Thecorresponding products were obtained in good selectivity (Scheme3).Scheme3Ag promoted trifluoromethylation of pyridine nitrogen oxides...