Synthesis, characterization and catalytic properties of metal porpholactones and cobalt(ii) porphyrin catalyzed alkylcarbene transfer reactions

Abstract

Transition metal-catalyzed nitrene and carbene transfer reactions are important methodologies for direct C-N and C-C bond formation and have found wide applications in organic synthesis. While metalloporphyrins are well-documented to be efficient catalysts for nitrene and carbene transfer reactions, the activity of their metal porpholactone analogues for these reactions remains underexplored. In this thesis, the syntheses of a series of novel metal porpholactone complexes are described, together with investigation of their spectroscopic, structural, electrochemical properties and catalytic properties towards nitrene transfer reactions. In addition to the catalyst, substituents of diazo compounds were found to have a significant influence on the reactivity and selectivity of the corresponding carbenoid. On the other hand, while acceptor carbenes have been extensively studied and have found many applications in organic synthesis, little is known about the reactive profile of alkylcarbenes. This thesis also describes studies on cobalt(II) porphyrin-catalyzed cyclopropanations of N-alkyl pyrrole with alkylcarbene and alkylcarbene C-H insertions, as well as their applications in constructing complex polycycles. A series of novel transition metal porpholactones, [RuII(CO)(TPPL)], [CoII(TPPL)], [CoII(F20TPPL)], [MnIII(OAc)(NMe2)4(F16TPPL)], and [FeIII(Cl)(NMe2)4(F16TPPL)] were synthesized and characterized. Moreover, the dioxo, bis-imido and carbene complexes of ruthenium porpholactone were synthesized and identified by 1H NMR and ESI-MS analysis. Among these complexes, [RuVI(NAr)2(TPPL)] and [RuIV(CHCO2Ar)(TPPL)] are the first isolated bis-imido and carbene complexes of ruthenium porpholactone. [MnIII(OAc)(NMe2)4(F16TPPL)] was found to be effective towards intra- and intermolecular nitrene sp3 C-H bond insertions; this complex can also efficiently catalyze difunctionalization of styrenes with ArNH2 and PhI(OAc)2. The reaction is believed to proceed via aziridination and subsequent ring opening. The imido intermediate of manganese porpholactone was detected by high-resolution ESI-MS. An efficient method has been developed for the rapid construction of a range of nitrogen-containing polycycles from simple starting materials by cobalt(II) porphyrin-catalyzed intramolecular cyclopropanation of N-alkyl pyrroles with alkylcarbene. By employing this method, a series of polycyclic cyclopropane-fused pyrrolines were obtained in moderate to high yields and with high chemoselectivity. The use of bulky 2,4,6-triisopropylbenzenesulfonyl hydrazones as carbene precursors enables the cyclopropanation to occur under milder conditions than their N-tosylhydrazone counterparts. Furthermore, a rapid approach to polysubstituted pyrrolizines and pyrrolizidines via cobalt(II) porphyrin-catalyzed cascade reaction was developed, in which pyrrolyl ketones undergo intramolecular cyclopropanation, ring opening and followed by oxidation or reduction. Alkyldiazomethanes in situ generated from N-tosylhydrazones derived from ethyl ketones were found to undergo intramolecular carbene sp3 C-H bond insertion catalyzed by cobalt(II) porphyrin to give pyrrolidines in moderate to excellent yields and with high chemoselectivity. This method was applied to the total synthesis of natural product Erythrinane.