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CYCLOADDITION REACTIONS OF ORGANOIRON(II) CYCLOPENTADIENE COMPLEXES. NEW SELECTIVE STEREOSPECIFIC TRANSFORMATIONS OF ORGANOIRON(II) COMPLEXES.The scope of the cycloaddition reaction between .eta.-5-cyclopentadienyliron(II) dicarbonyl-.eta.-1-cyclopentadiene (1.12a) and electrophilic olefins (1.4) and acetylenes (1.5) producing 7-syn-.eta.-5-cyclopentadienyliron(II) dicarbonyl-.eta.-1-bicyclo 2.2.1 hept-5-enes (2.1) and 7-syn-.eta.-5-cyclopentadienyliron(II) dicarbonyl-.eta.-1-bicyclo 2.2.1 hept-2,5-dienes (2.2), respectively, is found to be general for non-sterically hindered olefins and bis-activated acetylenes. The range of reactive 1.4 compounds is extended to include some sterically hindered olefins through precoordination of the olefin to diethylchloroalane or ethyldichloroalane. In contrast to all other acyclic cis and trans-1,2-disubstituted olefins, maleonitrile (1.41) cycloadds with 1.12a with complete retention of alkene stereochemistry. The relative rates for the cycloaddition between 1.12a and 1.41 in benzene, dichloromethane, and methanol are found to be 1:2:4, respectively. These stereochemical and kinetic results are more consistent with a concerted 4+2 cycloaddition than a two-step dipolar 3+2 cycloaddition. A dramatic stereochemical dependence on solvent polarity is observed in the cycloadducts resulting from the reaction of 1.12a with 1.41. Depending on the solvent the Alder "endo" rule is obeyed (methanol) or flagrantly violated (benzene). Reaction of 2.1 with ammonium cerium(IV) nitrate, bromine, or chlorine in acetonitrile containing excess sodium azide gives bicyclo 2.2.1 hept-5-ene-7-syn-carbonylazides (3.4). The reaction is found to be general using 1,2-disubstituted 2.1 compounds with bromine or chlorine. The thermally induced rearrangement of 3.4 compounds in refluxing toluene-tert-butanol gives 7-syn-t-Boc-aminobicyclo 2.2.1 hept-5-enes (4.4) in good yield. This is the first high yield stereospecific synthesis of 4.4 compounds. Furthermore, the synthetic equivalency of 1.12a is shown to include 5-carbonylazide-1,3-cyclopentadiene (3.9) and 5-t-boc-amino-1,3-cyclopentadiene (4.5) as well as 5-carbomethoxy-1,3-cyclopentadiene (3.10) 11.12 .