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Paper

Org. Biomol. Chem., 2008, 6, 513 - 522, DOI: 10.1039/b716910h

Controlling cis/trans-selectivity in intramolecular Diels–Alder reactions of benzo-tethered, ester linked 1,3,9-decatrienes

Emma L. Pearson, Anthony C. Willis, Michael S. Sherburn and Michael N. Paddon-Row

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 -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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