Deux types de participation π lors de l'hydrolyse des diazocétones γ, δ‐insaturées par des acides aqueux et des superacides. L'ion oxo‐5‐norbornyle‐2

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Abstract
γ, δ‐Unsaturated diazoketones undergo acid catalysed hydrolysis accompanied by cyclisation; the latter is favoured by suitable geometry (cyclopentenes) and by substitution by methyl groups. If both are present, rate enhancement by anchimeric assistance has been observed. Hydrolysis of 4‐diazoacetyl‐cyclopentene (1) yields a product mixture similar to that formed during solvolysis of 5‐oxo‐norbornyl‐2‐endo brosylate (23) and quite different from that of the exo isomer. The results are interpreted in terms of a common intermediate, the 5‐oxo‐2‐norbornyl carbonium ion. Solvent participation in the transition state, i. e. partial SN2 character, is implied by the entropies of activation and by the action of an added nucleophile (Br−). In superstrong acids, a different type of cyclisation takes place, involving the carbonyl oxygen and the protonated CC double bond and forming tetrahydropyrane derivatives.

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