Heteroatomic coupling oxidation synthesis

DFT calculations combined with a distortion/interaction energy analysis showed that the anomalous Z selectivity observed in Wittig reactions of ( rt/j< -substituted benzalde-hydes is not caused by phosphoms-heteroatom interactions in the addition TS but is predominantly steric in nature. An efficient synthesis of olefins by the coupling of stabilized, semi-stabilized, and non-stabilized phosphorus ylides with various carbonyl compounds in the presence of silver carbonate has been reported. The first catalytic (in phosphane) Wittig reaction has been developed by utilizing an organosilane that chemoselectively reduces a phosphane oxide pre-catalyst to a phosphane. Sodium carbonate and A,A-diisopropyl-ethylamine have been employed as bases. The kinetic E/Z... 

Heteroatom-directed cyclometallation forms the basis of C-H functionalization strategies for heterocycle synthesis. An example is the Rh-catalysed oxidative coupling of 3-phenylpyrazoles (1) with 4-octyne (2) to give pyrazoloisoquinolines (3) [66]. The proposed catalytic cycle for this process is shown in Fig. 11 and was supported by DFT calculations (BP86) using both a simple model system [Model 1 3-phenylpyrazole reacting with HC=CH at CpRh(OAc)2] and the full system used experimentally [Model 2 3-phenyl-5-methylpyrazole reacting with 4-octyne at... 

The copper-catalyzed synthesis of carbazoles from 2-aminobiphenyls via intramolecular C-H amination also could be realized using Mn02 as terminal oxidant (Scheme 8.42). The picolinamide-based bidentate directing group which could be spontaneously removed after the coupling reaction was crucial for this reaction. This Cu(OAc)2 catalytic system could proceed smoothly under I(III)-free conditions. Moreover, a few of heteroatom-containing carbazole core r-systems could be contained easily under the mild Cu(0Ac)2/Mn02 catalytic conditions [80]. 

The reaction of certain palladium-heteroatom complexes to alkenes and alkynes is a versatile tool for the synthesis of alkanes and alkene having heteroatoms attached. In particular, the various B-B, B-Si, and B-Sn compounds can be used for palladium-catalyzed borylation of alkenes and alkynes (Scheme 5-2). Borostannylation takes place at ambient temperature, whereas silylboration " only proceeds at a temperature above 80 °C due to the slow oxidative addition of a B-Si bond to a palladium(O) catalyst. Both reactions selectively provide cz j-products via addition of silicone or tin to the internal carbon and boron. The reactions are compatible with various functional groups for both terminal and internal alkynes. Cross-coupling reaction of boranes with organic halides selectively occurs at the terminal C-B bonds to provide regiodefined and stereodefined alkenylboron, alkenylsilicon, and alkenyltin compounds. 

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