STEREOCONTROL DURING THE ALKYLATION OF ENOLATES ATTACHED TO PI-ALLYL-MO(CO)2CP SYSTEMS

The preparations of dicarbonyl(η5-cyclopentadienyl)(1-3-η-5-oxocyclohexenyl)molybdenum (4) and dicarbonyl-(η5-cyclopentadienyl)(1-3-η-5-oxocycloheptenyl)molybdenum (27) are described. Deprotonation of 4 using lithium diisopropylamide at-100 °C, followed by treatment of the enolate with electrophiles (alkyl halides, benzaldehyde, Michael acceptors), leads to stereospecific alkylation at C-4 anti to the Mo(CO)2Cp group. Deprotonation of the alkylation products occurs regiospecifically at C-6 and enolate alkylation gives 4-exo, 6-exo-disubstituted complexes stereospecifically. The corresponding seven-membered ring complex 27 is deprotonated regiospecifically at C-4 on treatment with base, and the enolate can be alkylated stereospecifically anti to the metal. The stereochemical outcome of nucleophile addition to the ketone of the alkylation products from 4 and 27 is different and is explained on the basis of conformational arguments. The conformation of the cycloheptenyl complexes 25 and 31a were confirmed by single-crystal X-ray structure determination. C14H16O3Mo (25) crystallizes with space-group symmetry of P21/c. The unit-cell dimensions were a 11.694 (4), b 17.775 (6), c 13.114 (4) A, β 96.38 (3)°, V 2708.9 (15) A3, and Z = 8. The structure was refined to convergence with a final value of R = 4.28%, Rw = 6.38% (F ≥ 6.0σ). Similarly, C6H20O3Mo (31a) crystallized with space-group symmetry of P21/c. The unit cell dimensions were a 9.719 (3), b 12.955 (4), c 12.120 (4) A, β 103.48 (2)°, V 1484.1 (8) A3, and Z = 4. This structure was refined to final values of R = 2.77%, Rw = 5.13% (F ≥ 6.0σ). © 1990, American Chemical Society. All rights reserved.