Oxidative coupling rhodium chloride

Other functionalizations described include the direct alkylation of the title compound. For example, it was demonstrated that applying similar alkenes describe vide supra under rhodium catalysis leads to a direct hydroalkenylation, furnishing the corresponding 2-alkyl pyridine -oxides. Conversely, benzyl chlorides were effectively coupled to the title compound under similar conditions described for direct sp arylation (eq 30). ... 

The mechanism proposed was confirmed by the work of Cariati et al. [43]. In addition to their studies on rhodium WGSR catalysis in acid media, Cheng and Eisenberg have also reported [27] that mixtures of platinum chloride and tin chloride are active WGSR catalysts in an acetic acid/HCl solvent system. They proposed the following mechanism (Scheme 7.2). The catalytic cycle appears to involve the Sn(ll)/Sn(IV) redox couple. The formation of H2 coincides with the oxidation of Sn(ll) to Sn(IV) and CO is oxidized to CO2 concurrent with reduction of Sn(IV) to Sn(II). 

Biaryls with axial chirahty were prepared by pyridine- or isoquinoline-directed rhodium-catalyzed coupling with alkynes (Scheme 65). A number of diaryl-substituted alkynes coupled with l-(naphthyl)isoquinoline in the presence of [RhCp Cl2]2 and AgSbF with a copper (II) acetate oxidant in excellent yields (90-98%). The coupling proceeded smoothly with 2-aryl substituted pyridines (89-99%). A number of substituents were tolerated on the pyridines at C-3, including methyl, chloride, and methoxy. The isoquinoline-based biaryls were easily oxidized with MCPBA to provide... 

Ring expansion with Tamura et al. s Beckmann reagent, followed by dechlorination with Zn-Cu couple in methanol saturated with ammonium chloride, provided key pyrrolidinone intermediate 197 in 72% overall yield from 193. The intermediate 197 was then converted by using selenium dioxide and tcrt-butyl hydroperoxide into allylic alcohol (62%), which yielded the desired 1,3-diol 198 through rhodium-catalyzed hydroboration and oxidation as a 1 1 mixture of diastereomers in 72% yield. A seven-step reaction sequence then converted the diol 198 into (-l-)-retronecine 199, which was indistinguishable from an authentic sample of the natural product obtained by hydrolysis of natural monocrotaline (Scheme 16.29). ... 

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