Attaque nucleophile du carbone central de l'enchainement cumule lors de la cyclisation de diols ω,ω′-alleniques

The cyclisation of allenic diols 3 and 4 in the presence of mercuric chloride or silver nitrate leads exclusively or predominantly to bicyclic acetals 6 and 8 resulting from an initial nucleophilic attack on the central allenic carbon. This regioselectivity depends on the presence of a terminal methylene in the unsaturation since diol 5 leads to the dihydropyrane 12 coming from the nucleophilic attack on the terminal allenic...