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The origin of the ligand-controlled regioselectivity in Rh-catalyzed [(2 + 2) + 2] carbocyclizations: steric vs. stereoelectronic effects.

ABSTRACT: 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 PPh3 and (S)-xyl-binap as ligands is both electronically and sterically controlled. For example, the ester functionality polarizes the alkyne ?* orbital to favor overlap of the methyl-substituted terminus of the alkyne with the p?-orbital of the alkenyl fragment of the rhodacycle during alkyne insertion with PPh3 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.

SUBMITTER: Crandell DW

PROVIDER: S-EPMC5510011 | biostudies-literature | 2015 Dec

REPOSITORIES: biostudies-literature

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The origin of the ligand-controlled regioselectivity in Rh-catalyzed [(2 + 2) + 2] carbocyclizations: steric vs. stereoelectronic effects.

Crandell Douglas W DW Mazumder Shivnath S Evans P Andrew PA Baik Mu-Hyun MH

Chemical science 20150825 12

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 PPh3 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 pπ-orbital of the alkenyl fragment of ...[more]

PMID: 28757978

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