NOVEL (IMINO-ETA(6)-ARENE)CHROMIUM COMPLEXES AND THEIR DIASTEREOSELECTIVE INTRAMOLECULAR HETERO-DIELS-ALDER REACTIONS

Novel (imino-eta6-arene)chromium complexes 3 with nonactivated olefins tethered to the 2-azadiene system were prepared and further used in a new diastereoselective intramolecular Lewis-acid-catalyzed hetero-Diels-Alder reaction to give (eta6-octahydroacridine)chromium complexes 4. The trans selectivity of the cyclization reaction is mainly controlled by the Cr-(CO)3 fragment and to a minor extent by the catalyst, solvent, and substituents. Complexes 4 also could be obtained by a one-pot reaction starting from aldehyde 1, (o-toluidine)Cr(CO)3 (2), and Lewis acid. The stereochemistry of 4a was established by single-crystal X-ray structure analysis. Compound 4a crystallized in the monoclinic space group P2(1)/c with a = 9.518(1) angstrom, b = 12.456(1) angstrom, c = 16.457(1) angstrom, beta = 90.79(1)-degrees, V = 1950.8 angstrom3, Z = 4, R = 0.038 R(w) = 0.045, and T = 293 K for 343 parameters and 4426 reflections.