Palladium in azaheterocyclic synthesis: α-arylation of sulfones, domino processes and C-H carbene insertion reactions
Among transition metals used in organic chemistry, palladium has greatly contributed to the development of modern organic synthesis. This thesis is focused on the development of novel and efficient methodologies for the synthesis of nitrogen heterocycles employing palladium catalysed reactions. In t...
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| Tipo de recurso: | tesis doctoral |
| Estado: | Versión publicada |
| Fecha de publicación: | 2018 |
| País: | España |
| Institución: | CBUC, CESCA |
| Repositorio: | TDR. Tesis Doctorales en Red |
| OAI Identifier: | oai:www.tdx.cat:10803/586010 |
| Acceso en línea: | http://hdl.handle.net/10803/586010 |
| Access Level: | acceso abierto |
| Palabra clave: | Síntesi orgànica Síntesis orgánica Organic synthesis Catàlisi Catálisis Catalysis Pal·ladi (Element químic) Paladio Palladium Ciències de la Salut 547 |
| Sumario: | Among transition metals used in organic chemistry, palladium has greatly contributed to the development of modern organic synthesis. This thesis is focused on the development of novel and efficient methodologies for the synthesis of nitrogen heterocycles employing palladium catalysed reactions. In this work, DFT calculations complement the experimental work in order to gather mechanistic insights of the reported transformations. In the first part of the thesis an exhaustive study of the intramolecular palladium catalysed α-arylation of sulfones is described. This metal-mediated process was successfully combined with conjugated additions to generate domino processes of two, three and four steps that allowed the synthesis of functionalised indoles and tetrahydroisoquinolines. From a mechanistic point of view, DFT calculations suggest that a concertated metalation-deprotonation process followed by reductive elimination is involved in the indole ring formation. Next, the intramolecular palladium catalysed α-arylation reaction was explored using nucleophiles derived from sulfonates, sulfonamides and phosphonates. Although feasible, these nucleophiles are less efficient in the intramolecular cyclization leading to the tetrahydroisoquinoline ring. Domino processes based on α-arylation/Michael addition reactions starting from sulfonates and sulfonamides using diverse Michael acceptors were also reported. Attempts to pursue domino process starting from phosphonates were unsuccessful. In the second part of the thesis, a synthetic methodology for the synthesis of nitrogen heterocycles based on palladium catalysed decomposition of α- diazoacetamidas was studied. Decomposition of α-diazo-α-(methoxycarbonyl) acetanilides catalyzed by palladium leads to the chemoselective Csp2-H insertion and the synthesis of oxindole type products. Although Pd(0) and Pd(II) catalysts are able to promote this transformation, Pd(0) catalysts such as Pd2(dba)3 or [IMes)Pd(NQ)]2 yield the best results. DFT calculations suggest that the insertion reaction involves a novel stepwise mechanism that implies a palladium mediated 1,5-hidrogen migration followed by reductive elimination that yields two products: the insertion product and the Pd(0) catalyst. Finally, we studied the palladium catalysed decomposition of α-diazo-α- (methoxycarbonyl) acetamides to promote intramolecular Csp3-H insertion to form β-lactams. In these transformations, though both Pd (0) and Pd(II) catalysts can be used, Pd(II) complexes were found to be the most versatile and efficient. |
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