REGIOCHEMISTRY OF NUCLEOPHILIC-ADDITION TO CYCLOHEXADIENYL-IRON COMPLEXES HAVING STERICALLY DEMANDING SUBSTITUENTS

The reactions of sterically hindered tricarbonyl(cyclohexadienylium)-iron with nucleophilic reagents have been studied. The influence of the 4-alkoxyl substituents versus the bulkiness of the 1-alkyl substituents on the regioselectivity of nucleophilic addition was investigated. With sodium borohydride as nucleophile, substantial addition at the C-1 dienylium terminus was observed to take place via the more crowded endo face to give the more stable exo product. We here report the importance of steric hindrance to the approach of nucleophiles versus product stability during nucleophilic addition to the dienylium complexes.