REGIOSELECTIVITY OF NUCLEOPHILIC ADDITIONS TO (ARENE)CHROMIUM COMPLEXES - CONFORMATIONAL EFFECTS OF CR(CO)3 MOIETIES AND THE NATURE OF CARBANIONS

Nucleophilic addition of some carbon nucleophiles to tricarbonyl(1-exo-isopropyl-5-methoxytetralin)-chromium (4), tricarbonyl(1-endo-isopropyl-5-methoxytetralin)chromium (5), and tricarbonyl(1-isopropyl-5-methoxy-3,4-dihydronaphthalene)chromium (8) has been investigated. The regioselectivity of the nucleophilic addition using 2-lithio-1,3-dithiane under kinetic control conditions is dependent on the conformation of the Cr(CO)3 group for the arene ring. exo-Isopropyl complex 4 gives the meta-substituted compound with high regioselectivity in good yield, while the corresponding endo-isopropyl complex 5 yields predominantly the ortho-substituted arene. The crystal structure of the endo-complex 5 has been determined by X-ray crystallography, indicating that three CO ligands adopt the staggered conformation for the aromatic ring. On the other hand, the addition reaction with nitriles or cyanohydrin-stabilized carbanions under thermodynamic conditions provide the high meta-selectivity, regardless of the conformation of the Cr(CO)3 moiety.