VERSATILITE DE REACTIVITE DE L'ACETYLENE DICARBALDEHYDE ET DES ALDEHYDES α-ACETYLENIQUES A L'EGARD DES DIENES CONJUGUES CYCLIQUES ET HETEROCYCLIQUES EN MILIEU ACIDE

Article abstract of DOI:10.1016/S0040-4020(01)87436-6

The preparation of acetylenedicarbaldehyde 1 and the corresponding mono acetal 2 is described.A comparison of their reactivity with other α-acetylenic aldehydes RCCCHO 3 to 9 towards conjugated cyclic or heterocyclic dienes is presented.Under neutral conditions, the only expected Diels-Alder adducts I are formed.Under acidic conditions (HCO2H, CF3CO2H or eventually AcOH) they afford the only Diels-Alder adduct I when the cyclodiene does not present any aromatic character, and, on the opposite case, the Michael adducts II with more or less important amounts of I; starting from furan, a third pathway could also be observed dealing with t he formation of the double electrophilic substitution compounds III.The mechanisms are discussed and particularly, a common dipolar intermediate P is suggested to account for the competitive formation of I and II.