Controlling cis/trans-selectivity in intramolecular Diels-Alder reactions of benzo-tethered, ester linked 1,3,9-decatrienes |
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Authors: | Pearson Emma L Willis Anthony C Sherburn Michael S Paddon-Row Michael N |
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Affiliation: | Research School of Chemistry, Australian National University, Canberra, ACT 0200, Australia. |
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Abstract: | Predictions from DFT (B3LYP/6-31 G(d))-computed stereoisomer product distributions for intramolecular Diels-Alder (IMDA) reactions have been successfully replicated in the laboratory. Benzo-tethered hexadienyl acrylates generally undergo moderately trans-selective IMDA reactions which, as suggested by DFT calculation, arise from two opposing transition structure (TS) features: stabilising secondary orbital interactions, which are stronger in the cis-TSs, and stabilising pi-conjugative interactions between the benzo moiety and the 1,3-diene component - which are stronger in trans-TSs. Substrates carrying a removable substituent (i.e. Br or TMS) at C3 of the diene or C12 of the aromatic ring are predicted to undergo highly cis-selective thermal IMDA reactions by steric destabilisation of the trans-TS. A substrate carrying a two atom tether between C3 and C12 is predicted to undergo a highly trans-selective intramolecular cycloaddition by destabilisation of the cis-TS. These calculations are borne out experimentally. |
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