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The origin of the ligand-controlled regioselectivity in Rh-catalyzed [(2 + 2) + 2] carbocyclizations: steric vs. stereoelectronic effects
Density functional theory calculations demonstrate that the reversal of regiochemical outcome of the addition for substituted methyl propiolates in the rhodium-catalyzed [(2 + 2) + 2] carbocyclization with PPh(3) and (S)-xyl-binap as ligands is both electronically and sterically controlled. For exam...
Autores principales: | , , , |
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Formato: | Online Artículo Texto |
Lenguaje: | English |
Publicado: |
Royal Society of Chemistry
2015
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Materias: | |
Acceso en línea: | https://www.ncbi.nlm.nih.gov/pmc/articles/PMC5510011/ https://www.ncbi.nlm.nih.gov/pubmed/28757978 http://dx.doi.org/10.1039/c5sc02307f |
Sumario: | Density functional theory calculations demonstrate that the reversal of regiochemical outcome of the addition for substituted methyl propiolates in the rhodium-catalyzed [(2 + 2) + 2] carbocyclization with PPh(3) and (S)-xyl-binap as ligands is both electronically and sterically controlled. For example, the ester functionality polarizes the alkyne π* orbital to favor overlap of the methyl-substituted terminus of the alkyne with the p(π)-orbital of the alkenyl fragment of the rhodacycle during alkyne insertion with PPh(3) as the ligand. In contrast, the sterically demanding xyl-binap ligand cannot accommodate the analogous alkyne orientation, thereby forcing insertion to occur at the sterically preferred ester terminus, overriding the electronically preferred orientation for alkyne insertion. |
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