Reaction of transition metal carbonyls with heterocyclic systems-III. S_N2′-type reaction of complexed π-allyl systems

A proposition regarding the capability of a complex π-allyl system to undergo a displacement reaction was advanced (eqn 2) and examined experimentally. A unique structural feature of this system is the four rather than three C atoms which intervene between the displaced and entering groups. The experiment was carried out using lactone 1c which is internally complexed and was properly labelled with deuterium. The product of its reaction with aniline has been found to be rearranged with respect to the D label, thus substantiating an S_N2′-type mechanism in a complexed π-allyl system (eqn 2). From an intramolecular comparison study of the reactivity of an allyl and complexed π-allyl system in S_N2′-type displacement reactions using compound 10, it was concluded that the latter is more reactive than the former. Furthermore, the π-allyl lactone 12, in which the displaced and entering groups are separated by three C atoms, was also found to undergo a displacement reaction.