Synthesis of diversely functionalized pyrrolizidines and indolizidines using olefin ring-closing metathesis

Various nitrogen-fused tricyclic compounds, having benzoindolizidine and benzopyrrolizidines ring systems were synthesized via ene–ene metathesis using the first and second-generation Grubbs catalyst. The ene–ene metathesis proceeded smoothly in refluxing CH2Cl2 with 3.0 mol % of G1, giving good yields (78–86%) of the benzoindolizidine products 12a,b. The benzopyrrolizidine 6 was prepared after optimization in 64% yield by using 5.0+5.0 mol % of G2. The resulting olefin moiety of the indolizidine framework is a suitable precursor for polyhydroxy structures via the Sharpless process. The structures of the polyhydroxylated adducts were determined by 1H NMR spectra and single-crystal X-ray analysis.

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