Olefin-tethered amides

J.K. Cha et al. developed a stereocontrolled synthesis of bicyclo[5.3.0]decan-3-ones from readily available acyclic substrates. Acyclic olefin-tethered amides were first subjected to the intramolecular Kulinkovich reaction to prepare bicyclic aminocyclopropanes. This was followed by a tandem ring-expansion-cyclization sequence triggered by aerobic oxidation. The reactive intermediates in this tandem process were aminium radicals (radical cations). The p-anisidine group was chosen to lower the amine oxidation potential. This substituent was crucial for the generation of the aminium radical (if Ar = phenyl, the ring aerobic oxidation is not feasible). 

Cha and coworkers [15] described an interesting example of a radical/cation-mediated domino reaction for the stereoselective preparation of bicyclo[5. B.Ojdecan-3-ones 31 using aminocyclopropane 30 as substrate which was prepared by employing an intramolecular Kulinkovich cydopropanation of olefin-tethered amide. 

After successful application of the silver catalyst shown in olefin aziridination (Section 6.1.1), He and coworkers showed that intramolecular amidation was possible with both hydrocarbon-tethered carbamates and sulfamate esters.24 They found that only the Bu3tpy silver complex could catalyze efficient intramolecular amidation, while other pyridine ligands gave either dramatically lower yields or complicated product mixtures. In an interesting control study, both copper and gold were also tested in this reaction. Both the copper and gold Bu tpy complexes can mediate olefin aziridination, but only silver can catalyze intramolecular C-H amidation, indicating that the silver catalyst forms a more reactive metal nitrene intermediate. 

Padwa subsequently described some intramolecular versions of this reaction. A structurally similar aryl ester, 55, a tethered to a terminal olefin was subjected to rhodium-catalyzed diazo decomposition. Carbonyl ylide formation followed by intramolecular cycloaddition resulted in tricyclic product 56 a, Eq. 39 [66 - 69]. Cycloaddition also occurred with the amide analogue 55 b. 

Few examples of intramolecular additions of amines to alkenes catalyzed by late transition metals have been published more examples of the additions of amides, carbamates, and tosylamides to alkenes catalyzed by this type of complex have been reported. Addition of a secondary amine across a tethered olefin catalyzed by a simple platinum-halide complex is shown in Equation 16.65a. A more recent catalyst based on [Rh(COD)JBF and a biaryldialkylphosphine leads to cyclizations of aminoalkenes with greater scope (Equation 16.65b). These reactions occur to form five- and six-membered rings, with or without groups that bias the system toward cyclization. They also occur with both internal and terminal olefins and with both primary and secondary amines. 

Catalyst Cl promoted Alder-ene type cyclizations of 1,6-enynes with sterically congested, trisubstituted double bonds and either ether or amide functions in the tethering chain (Fig. 10.27). These reactions afforded the expected dihydrofuranes and pyrrolines with high levels of enantioselectivity. Minor amounts of the isomerized endo-olefin product B were occasionally isolated. 

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