Catalytic Iron-Mediated [4 + 1] Cycloaddition of Diallenes with Carbon Monoxide

Abstract

Conjugated diallenes undergo stereoselective [4 + 1] cycloadditions in a variety of solvents. Accelerated thermal exchange of CO in Fe(CO)5 is catalyzed by the diallene substrate, consistent with the previous kinetic analysis. The Eyring activation parameters were determined to be ΔH⧧ = 16.2 (±0.7) kcal mol-1 and ΔS⧧ = −17.9 (±2.3) cal mol-1 K-1. The negative entropy of activation is consistent with rate determining associative coordination of diallene to form a diallene−iron complex. The effect of coordinating solvents on this cycloaddition reaction suggests that the synthetic utility of these transformations can now be expanded to include diallenes with functional groups that may only weakly coordinate to the iron. Only one sterically demanding substituent on the diallene termini is necessary to give good π-facial selectivity, which also expands the synthetic utility of these transformations.