SYNTHESIS, PROPERTIES, AND REACTIONS WITH C-NUCLEOPHILES OF (PHENYLOXAZOLINE)TRICARBONYLCHROMIUM(O), (PHENYLMETHANIMINE)TRICARBONYLCHROMIUM(O), AND (BENZALDEHYDE HYDRAZONE)TRICARBONYLCHROMIUM(0) COMPLEXES

The title complexes react efficiently with carbon nucleophiles to give ortho addition products with good to excellent regioselectivity. 2-Li thio-2-methylpropionitrile substantially adds meta and para at low tem perature but rearranges at 0-degrees-C to give predominantly ortho sel ectivity. Smaller nucleophiles (LiCH2S(O)C6H4-P-Me, LiCH2CO2-t-Bu) and simple alkyllithium reagents (MeLi, n-BuLi, t-BuLi (in the absence of HMPA), (vinyl)Li, PhLi) exclusively add ortho to the functional group . Arene lithiation is not a competitive reaction with these complexes. Oxidative (12) decomplexation yields the free 1,2-disubstituted arene s. Under the workup conditions the phenyloxazolines ortho substituted by a 2-methylpropionitrile, 2-propionitrile, or acetonitrile group are not stable. Intramolecular addition of oxazoline to the nitrile leads to the carboxylic acid in the first case and to isoquinolone products in the two other cases. ortho regioselectivity is ascribed to chelati on of the incoming organolithium reagent. The rearrangement of the nit rile-stabilized nucleophiles shows that ortho addition is also favored thermodynamically. ortholpara regioselectivity is assisted by the ele ctron-withdrawing nature of the oxazoline and methanimine functions. T he aldehyde hydrazone function, however, is shown to have resonance do nor character, and the exclusive ortho addition here must be ascribed entirely to the chelation effect.