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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
Author(s) -
Malherbe Roger,
Dahn Hans
Publication year - 1974
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/hlca.19740570822
Subject(s) - chemistry , carbonium ion , solvolysis , medicinal chemistry , hydrolysis , 2 norbornyl cation , protonation , cyclopentene , sn1 reaction , stereochemistry , nucleophile , ion , organic chemistry , catalysis
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 S N 2 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 CC double bond and forming tetrahydropyrane derivatives.