The process of electroreductive cyclization (ERC) occurs when an electron deficient alkene is electrochemically reduced, and thus able to react with another electron deficient alkene.  This type of reaction in which two electrophiles are brought to react together is difficult to bring about without the use of electrochemistry, yet is a key step in the chemical synthesis of many natural products.  Reduced metal-salen compounds can be used to mediate electron transfer to the ERC substrate.  Previous theoretical work has determined that an inner-sphere electron transfer is favorable for nickel(II)-salen.  For this computational study, the mechanism of substrate cyclization following this electron transfer will be investigated.  Two pathways will be examined for the cyclization of two ERC substrates, an a, �-unsaturated ester and aldehyde.  The first is a concerted pathway, where cyclization and separation of the substrate from the metal-salen occur at the same time.  The second is a stepwise pathway, where the substrate detaches from the metal-salen yielding an intermediate radical carbanion, which then proceeds to subsequently cyclize.  Using density functional theory (DFT) calculations, the thermodynamics for the ERC reactions are studied, and the kinetically preferred pathway for each substrate is determined.  The results will be significant since viability of the concerted pathway is critical for obtaining stereoselectivity during the cyclization reaction and maximizing the potential for the utility of ERC in organic synthesis.

Computational study of the mechanism of metal-salen mediated electroreductive cyclization reactions

248th National Meeting (2014)

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