Facile Dearomatization of Nitrobenzene Derivatives and Other Nitroarenes with N‐Benzyl Azomethine Ylide

1,3-Dipolar cycloaddition reactions of azomethine ylides with aromatic dipolarophiles

“…69,70 Thus, Nbenzylazomethine ylide 49b can be formed in situ from reaction of N-methoxymethyl-(Ntrimethylsilylmethyl)benzylamine 56 and a catalytic amount of trifluoroacetic acid at 0 °C to room temperature (Scheme 14). [71][72][73] Consistent with the earlier work of Gribble, 68 2-nitro-1-tosylindole 57 underwent efficient cycloaddition reaction to afford the tricyclic product 58 in excellent yield (Scheme 15).…”

“…56 for 22 h). 69,70 Cycloaddition reactions of nitropyridines were also explored. 69,70 While nitropyridine and nitropyridine-N-oxide failed to react with azomethine ylide 49b, 3,5-dinitropyridine 69 underwent rapid reaction to give a tris cycloadduct 70, whose stereochemistry was established as syn-anti by 2D NOESY experiments (Scheme 18).…”

“…69,70 Cycloaddition reactions of nitropyridines were also explored. 69,70 While nitropyridine and nitropyridine-N-oxide failed to react with azomethine ylide 49b, 3,5-dinitropyridine 69 underwent rapid reaction to give a tris cycloadduct 70, whose stereochemistry was established as syn-anti by 2D NOESY experiments (Scheme 18). 70 Also, in a further interesting example, 4-nitroquinoline-N-oxide 71 underwent regioselective two fold cycloaddition reactions to both the C3-C4 double bond and the nitrone 1,3-dipole to give exclusively the anti bis adduct 72, with the structure and stereochemistry proven by X-ray crystallographic analysis (Scheme 18).…”

“…69,70 While nitrobenzene itself does not react to an observable extent with the ylide 49b, even with a large excess of the reagent 56, dinitrobenzenes such as 1,3-dinitrobenzene 84 and 1,4-dinitrobenzene 86 give bis adducts 85 and 87 in 85% and 69% yield, respectively (Scheme 24). No evidence for mono adducts were observed in these reactions, indicating that the mono adduct must be much more reactive towards azomethine ylide 49b than the starting material.…”

“…69,70 Whilst theoretically there are four potential anti bis adducts that could arise from 3-chloronitrobenzene 90 and 3,4-dichloronitrobenzene 91, only single regiosiomeric bis adducts, 92 and 93 were obtained, respectively (Scheme 26). In contrast, the reactions of the corresponding 3-trifluoromethyl-1-nitrobenzene derivatives 94 to 97 delivered a range of products depending on the analogue (Scheme 27).…”