Plausible mechanism of this reaction is illustrated in Scheme 7. The reaction should proceed by the same route1 as the reaction of 1 with 2, and the primary adduct anion [A] is methylated10 with the methyl ether 1 to afford 4a.
Furthermore, heats of formation of a primary adduct (18), 11 and an intermediate [C] were calculated by PM3, and compared with those of the corresponding compounds observed1 in the reaction of perfluoro(2-methylpent-2-ene) 2, as shown in Fig. 1. The difference in heat of formation between 11 and [C] (delta H = 14.7 kcal mol-1; 1 cal = 4.184 J) is larger than that between 17 and [B] (delta H = 7.87 kcal mol-1). This result may be able to explain the stubbornness of 11 to cyclization.
Fig. 2 Optimized structures of (11) and [C] by PM3 (MOPAC)