Stereoselective Control in the Base‐Catalyzed H/D Exchange of 5,6‐Dimethylidene‐2‐bicyclo[2.2.n]alkanone Tricarbonyliron Complexes. Revision of the Structures of Tricarbonyliron Complexes of 5,6‐Dimethylidenebicyclo[2.2.2]oct‐2‐ene and 5,6‐Dimethylidenebicyclo[2.2.1]hept‐2‐ene

Oxidative hydroboration of exo ‐ ( 1 ) and end ‐Fe(CO) 3 ( 2 ) complexes of 5,6‐dimethylidenebicyclo[2.2.2]oct‐2‐ene are highly stereoselective and give endo ‐alcohol 3 and exo ‐alcohol 4 as major products, respectively, Collins oxidations of 3 and 4 furnish the corresponding exo ‐Fe(CO) 3 ‐complexed 5,6‐dimethylidene‐2‐bicyclo‐[2.2.2]octanone 7 and 8 . NaBH 4 reduction of exo ‐complexes 7 gives a mixture of 3 and isomeric exo ‐alcohol 18 , whereas reduction of endo ‐complexes 8 gives the endo ‐alcohol, endo ‐complexes 19 , as the sole product. The base‐catalyzed H/D exchange of 7 and 8 afford the dideuterated exo ‐complex 35 and the monodeuterated endo ‐complex 32 , respectively. Oxidative hydroborations of the exo ‐( 9 ) and endo ‐Fe(CO) 3 ( 10 ) complexes of 5,6‐dimethylidenebicyclo[2.2.1]hept‐2‐ene give the corresponding exo ‐alcohols 39 and 40 . Oxidation of 39 and 40 gives the exo ‐ and endo ‐complexes 41 and 42 , respectively, of 5,6‐dimethylidene‐2‐bicyclo[2.2.]heptanone. Only H exo C(3) can be exchanged in 42 , wheres both H ‐atoms at C(3) in 41 are exchangeable. The endo ‐Fe(CO) 3 group in 8 and 42 blocks the base‐catalyzed H/D exchange of H endo C(3), thus providing a test for the configuration of Fe(CO) 3 group in these systems. These studies have led to a revision of the iron configurations proposed by Hansen et al , [2] for 1, 2, 9 and 10 .