STEREOSPECIFIC FUNCTIONALIZATION OF (PI-ALLYL)MOLYBDENUM COMPLEXES DERIVED FROM CYCLOPENTENONE - TOWARD THE STEREOCONTROLLED CONSTRUCTION OF SUBSTITUTED 2-CYCLOPENTENONES

(Eta5-cyclopentadienyl) eta)-1-oxo-2-cyclopenten-4-yl]dicarbonylmolybd enum on treatment with NOPF6 in 1,2-dimethoxyethane at 0-degrees-C evo lves CO and formed 4-eta)-1-oxo-2-cyclopenten-4-yl]nitrosylmolybdenum hexafluorophosphate in a highly diastereoselective manner. This electr ophilic species reacted with nucleophiles (higher-order cuprates, malo nates, enolates, and cyanoborodeuteride) to form )carbonyl(eta5-cyclop entadienyl)nitrosylmolybdenum complexes of 4-substituted 2-cyclopenten ones in good to excellent yields and with high regioselectivity. High yield oxidative demetallation with ceric ammonium nitrate provided the 4-substituted cyclopentenones. The product resulting from reaction of 4-eta)-1-oxo-2-cyclopenten-4-yl]nitrosylmolybdenum hexafluorophosphat e with Me2Cu(CN)Li2 was characterized by X-ray diffraction, proving th at the methyl group was delivered anti to the molybdenum atom and to t he 4-position of the cyclopentenone ligand. In the crystal structure, the metal carbonyl (Mo-CO) moiety is situated parallel to the metal ol efin unit while the metal nitrosyl (Mo-NO) bisects the olefin. The ste reochemistry at molybdenum relative to the 4-methylcyclopentenone liga nd (2S,3R,4S,MoR/2R,3S,4R,MoS) demonstrates that either the nucleophil ic attack has occurred trans to NO in the exo conformer of the eta3-al lyl or cis to the NO in the endo conformer. This stands in direct cont rast to earlier studies of unbiased cationic (pi-allyl)molybdenum nitr osyl complexes where nucleophilic addition occurred trans to the NO in the endo conformer and cis to the NO in the exo conformer. A parallel series of reactions (CO --> NO+ conversion then nucleophilic addition ) was conducted on yl[(2,3,4-eta)-1-oxo-5-methyl-2-cyclopenten-4-yl)] molybdenum. Small, sterically unbiased nucleophiles (NaCH(COOMe)2 and deuteride) reacted with high selectivity to produce cis-4,5-disubstitu ted cyclopentenones eta2-coordinated to molybdenum, while larger nucle ophiles [Me2Cu(CN)Li2 and NaC(Me)(COOEt)2] gave predominantly the 2,5- disubstituted cyclopentenone eta2-complex.