Chemo- and Stereoselective Coordination of 5,6-Dimethylidene-7-oxabicyclo[2.2.1]hept-2-ene by d8- and d6-Metal Carbonyls. Diels-Alder reactivity of Dienes Perturbed by Remote Olefin Complexation

The endocyclic double bond C(2), C(3) in 5,6-dimethylidene-7-oxabicyclo2.2.1]-hept-2-ene ( 1 ) can he coordinated selectively on its exo-face before complexation of the exocyclic s-cis-butadiene moiety. Irradiation of Ru₃(CO)₁₂ or Os₃(CO)₁₂ in the presence of 1 gave tetracarbonyl (1R,2R, 3S,4S)-2,3-η-(5,6-dimethylidene-7-oxabicyclo2.2.1]-hept-2-ene)]ruthenium ( 6 ) or -osmium ( 8 ). Similarly, irradiation of Cr(CO)₆ or W(CO)₆ in the presence of 1 gave pentacarbonyl(1R, 2R, 3S,4S)-2,3-η-(5,6-dimethylidene-7-oxabicyclo2.2.1]hept-2-ene)]chromium (10) or -tungsten (11) . Irradiation of complexes 6 and 11 in the presence of 1 led to further CO substitution giving bed-tricarbonyl-ae-bis(1R,2R,3S,4S)-2,3-η-(5,6-dimethylidene-7-oxabicyclo2.2.1]hept-2-ene)]ruthenium ( 7 ) and trans-tetracarbonyl(1R,2R,3S,4S)-2,3-η-(5,6-dimethylidene-7-oxabicyclo-2.2.1]hept-2-ene)]tungsten (12) , respectively. The diosmacyclobutane derivative cis-m?-(1R,3R,3S,4S)-(5,6-dimethylidene-7-oxabicyclo2.2.1]hepta-2,3-diyl)]bis(tetracarbonyl-osmium) (Os-Os) (9) wa also obtained. The Diels-Alder reactivity of the exocyclic s-cis-butadiene moiety in complexs 7 and 8 was found to be significantly higher than that of the free triene 1 .