Functionalizing heterocycles by electron-deficient bonding to a triosmium cluster

A new synthetic methodology for adding carbon-based nucleophiles to the car bocyclic ring of quinolines has been developed, based on the electron-defic ient bonding of the C(8) carbon and the protective coordination of the nitr ogen atom to the metal core in the complexes Os-3(CO)(9)(mu(3)-eta(2)-C9H5( R)N)(mu-H), 1a-1h. These compounds react with a wide range of carbanions (e .g., R'Li) to give the nucleophilic addition products Os-3(CO)(9)(mu(3)-eta (3)-C9H7(5-R')N)(mu-H), 2a-2l, and Os-3(CO)(9)(mu(3)-eta(3)-C9H6(3-, 4-, or 6-R)(5-R')N)(mu-H), 3b-3g, after quenching with trifluoroacetic acid, in i solated yields of 25-86%. ln the 6-substituted derivatives, this addition i s stereoselective, forming only the cis-diastereomer. In the case the 6-chl oro derivative, a second product is obtained, Os-3(CO)(9)(mu(3)-eta(2)-C9H5 (6-Cl)(5-C(CH3)(2)CN)N)(mu-H)(2) 4, the result of protonation at the metal core and rearrangement of the carbocyclic ring. The trans-diastereomer of t he 6-substituted derivatives can be obtained by quenching the intermediate anion of the unsubstituted complex with (CH3O)(2)SO2 or acetic anhydride. N ucleophilic addition to the 5-chloro complex occurs across the 3,4-bond to give OS3(CO)9(mu(3)-eta(2)-C9H6(5-Cl)(4-C(CH3)(2)CN)N)(mu-H), 5 The additio n products, types 2 and 3, can be rearomatized by reaction with diazobicycl ononane (DBU)/dichlorodicyanoquinone (DDQ) or by reaction of the intermedia te anion with trityl cation or DDQ. The resulting rearomatized complexes ca n be cleanly cleaved from the cluster by heating in acetonitrile under a CO atmosphere, yielding the functionalized quinoline and Os-3(CO)(12) as the only two products. Solid structures of cis-3e, ti ans-3e, 4, and 5 are repo rted.