o-Quinonoid compounds. Part 14. 1,5-Acyl shifts in substituted indenes: migratory aptitudes from racemisation rates
- 1 January 1978
- journal article
- research article
- Published by Royal Society of Chemistry (RSC) in Journal of the Chemical Society, Perkin Transactions 1
- No. 9,p. 1050-1058
- https://doi.org/10.1039/p19780001050
Abstract
Racemisation rates for the indenes (1) provide migratory aptitudes for acyl, vinyl, ethynyl, nitrile, and alkyl groups, as well as hydrogen. Migratory aptitude decreases in the order: HCO > Bz ∼ Ac > H > vinyl > CONHMe > CO2Ph > CO2Me > CN ∼ CCH > alkyl. It is suggested that a similar order may apply to all 1,5-sigmatropic shifts. It is proposed that the fast migration of formyl, acetyl, and benzoly groups is, at least in part, due to a secondary interaction involving the carbonyl π* orbital. Small substituent effects on the rearrangement of the p-substituted benzoylindenes, and small solvent rate effects suggest little increased polarity in the rearrangement transition states. Racemisation of (1; X = Ac) and (1; X = Bz) is accelerated in the presence of boron trifluoride–ether.Keywords
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