CATALYTIC IRON-MEDIATED [4-CYCLOADDITION OF DIALLENES WITH CARBON-MONOXIDE(1])

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 Delta H-double dagger = 16.2 (+/-0.7) kcal mol(-1) and Delta S-dou ble dagger = -17.9 (+/-2.3) cal mol(-1) K-1. The negative entropy of a ctivation is consistent with rate determining associative coordination of diallene to form a diallene-iron complex. The effect of coordinati ng solvents on this cycloaddition reaction suggests that the synthetic utility of these transformations can now be expanded to include diall enes with functional groups that may only weakly coordinate to the iro n. Only one sterically demanding substituent on the diallene termini i s necessary to give good pi-facial selectivity, which also expands the synthetic utility of these transformations.