Investigation Of Stoichiometric And Catalytic Palladium Mediated Reactions

This dissertation describes the investigation of stoichiometric and catalytic transformations involving Pd(II) compounds. The first two parts of the dissertation are focused on the preparation, characterization and application of the well-known group of Pd(II) derivatives called cyclopalladated complexes (CPCs). Specifically, N,N-dimethylhydrazone of D-camphor (I.1) was obtained as the single E isomer in 80% yield by treating the enantiopure ketone with N,N-dimethylhydrazine in the presence of an equimolar amount of p-TSA.H2O in ethanol. Direct cyclopalladation of hydrazone I.1 was accomplished at the C(3)H2 group using Pd(MeCN)2Cl2 and NaOAc in MeCN at the reflux temperature. The product of the reaction, dinuclear cyclopalladated complex (I.2), was isolated in 89% yield as a mixture of diastereoisomers, which differ by the absolute configuration of the chiral carbon bound to the metal. Compound I.2 was converted to the mononuclear complex I.3 by treating the dimer with PPh3. Compound I.3 was a mixture of two diastereomers with the Pd atom either in the endo or exo position of the bornane scaffold. Isomers of complex I.3 were partly separated by column chromatography to obtain samples of endo-I.3 and exo-I.3 with 96% and 86% de, respectively. The structures of two diastereomers, endo-I.3 and exo-I.3, were supported by 1H, 13C{1H}, 31P{1H} and 1D NOE NMR spectra and X-ray crystallographic data.The dimeric complex I.2 (named as II.12 in Chapter II) and five known (sp2)C,N and (sp3)C,N cyclopalladated complexes (II.1, II.4, II.6, II.8, and II.10) derived from N,N-dimethylbenzylamine, 4,4-dimethyl-2-phenyl-2-oxazoline, 2-tert-butyl-2,2-dimethyl-2- oxazoline, O-methyloxime of D-camphor, and 8-methylquinoline were used in C–C bond formation reactions with aryl, benzyl and allylboronic acids or esters. Two protocols for a C–C coupling were developed; both involve the use of a base and the conversion of dimeric cyclopalladated complexes to the mononuclear derivatives with PPh3 as an auxiliary ligand. The (sp2)C–(sp2)C bond formation was successfully achieved by reacting complexes PPh3-II.1 and PPh3-II.4 with ArB(OH)2 in acetone at 60 oC in the presence of Cs2CO3, and the corresponding products II.3 and III.5 were isolated in 73–90%. Reactions of (i) (sp3)C,N complexes PPh3-II.6, PPh3-II.8, and PPh3-II.10 with ArB(OH)2 (Ar = Ph, p-NO2C6H4, p-MeOC6H4, 8-quinolyl and 2-pyridyl) and (ii) (sp2)C,N palladacycle PPh3-II.4 with pinacol esters of allyl- and benzylboronic acids occurred in a refluxing 4:1 mixture of dioxane-water in the presence of K3PO4 and afforded (sp2)C–(sp3)C coupling products II.7, II.9, II.11 and II.15 in 46–89% yield. Compounds II.16b–II.18b with an (sp3)C–(sp3)C bond were isolated in 67, 38, and 17% in the reactions of pinacol ester of benzylboronic acid with (sp3)C,N palladacycles PPh3-II.6, PPh3-II.8, and PPh3-II.10, respectively. The stereoselectivity of the transformation was investigated using reactions of p-NO2C6H4B(OH)2 with two diastereomeric complexes having different absolute configurations of the chiral center attached to the metal, (1R,2S,4R,Z)-II.12 and (1R,2R,4R,Z)-II.12. Both reactions yielded the same isomer, (1R,3R,4R,Z)-II.13b. The X-ray crystallographic data of (1R,3R,4R,Z)-II.13b were obtained. In the third part of the dissertation, the Pd-catalyzed arylation of arylboronic acids with triarylphosphines was investigated. Various parameters of this transformation, such as the oxygen presence, choice of solvent, temperature, palladium source, bases and oxidants, were tested and the optimal conditions of the aryl transfer were determined. The effect of electron-withdrawing and electron-donating substituents on the aryl groups of both reactants was also studied. The unusual transfer of the acetate group from Pd(OAc)2 to p-nitrophenylboronic acid in the presence of PAr3 was observed. A plausible mechanism of the Pd-catalyzed aryl group transfer from PAr3 to the arylboronic acid was proposed

A Sonochemical Approach to 3-(het)aryl Substituted 1H-[1,3]oxazino[3,4-a]indol-1-One Derivatives Promoted by Pd/Cu-Catalysts and ZnCl2

A new approach has been developed for the access of 3-(het)aryl substituted 1H-[1,3]oxazino[3,4-a]indol-1-one derivatives promoted by Pd/Cu-catalysts and ZnCl2. These compounds were prepared via a direct and one-pot method involving the coupling of 2-iodoindole derivatives with a range of terminal alkynes in the presence of (PPh3)4Pd, CuI and ZnCl2 in DMF under ultrasound. This sonochemical approach proceeded via the CC coupling followed by intramolecular cyclization (i.e. CO bond formation) in a regioselective manner in the same pot affording the desired products in good to acceptable yield. The mild reaction conditions, shorter duration and the use of eco-friendly energy are some of the key features of the current methodology. Among the synthesized compounds, the [1,3]oxazino[3,4-a]indol-1-one derivative 3a, 3c and 3f were identified as the preliminary hits when tested in vitro for their TNF-α inhibitory potential