ASYMMETRIC INDUCTION IN ETA(2)-ARENE COMPLEXES OF PENTAAMMINEOSMIUM(II)

A series of eta(2)-arene complexes (2a-i) of the form [Os(NH3)(5)((ArO CHRCH3)-C-1)](2+) was prepared in which the alkoxy substituent R-1 bea rs a potential hydrogen bond acceptor. Using an ester or amide group a s the hydrogen bond acceptor, a two-point interaction was achieved bet ween the pentaammineosmium system and the organic ligand. For these co mplexes, a single coordination diastereomer was observed. For compound 2a, evidence for hydrogen bonding between the carbonyl oxygen and the pentaammineosmium fragment was obtained through H-1 NMR studies and b y a comparison of the rate of arene displacement for 2a compared to th at of the parent complex [Os(NH3)(5)(anisole)](2+). Complex 2a undergo es stereospecific protonation to form a 4H-anisolium product 3a. Compl ex 3a undergoes nucleophilic addition of a silylketene acetal at C3 to generate an alkoxydiene complex (4) as a single diastereomer. Hydroly sis of 4 removes the chiral auxiliary, and subsequent oxidative decomp lexation yields a cyclohexenone with a new stereogenic center.