Experimental and Theoretical Studies on the Bismuth-Triflate-Catalysed Cycloisomerisation of 1,6,10-Trienes and Aryl Polyenes

Cycloisomerisation of polyenes such as diethyl geranylprenylmalonate [(E)-1a], diethyl geranylphenylmalonate [(E)-2a] and diethyl cinnamylgeranylmalonate [(E,E)-3a] catalysed by bismuth triflate was studied from experimental and theoretical viewpoints. Several intermediates were isolated and characterised, and calculated transition-state structures are proposed for the three reactions. The diastereoselectivity observed during the reaction of (E)- or (Z)-2a in favour of the formation of trans-fused bicyclic products is discussed in detail. The nature of the active catalytic species derived from bismuth triflate was also investigated, and the formation of a hybrid Lewis acid/Bronsted acid catalyst with water molecules is proposed, supported by experimental and theoretical data.