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The reaction of the zwitterionic intermediate, generated in situ from either tert-butylisocyanide or cyclohexylisocyanide and acetylenedicarboxylates, with 3-cyanochromones is described, whereupon spirochromenofuran derivatives 5 or 6 were obtained in good yields. The subsequent acid-catalyzed rearrangement of the isolated 2-imino-spirochromenofurans 5 to 2-amino-spirochromenofurans 7 has also been studied. Rational mechanistic schemes for the formation of compounds 5, 6, and 7 are proposed. The structure elucidation of the products was accomplished by 1D and 2D NMR experiments and confirmed by X-ray crystallographic analysis. Full assignment of all (1)H and (13)C NMR chemical shifts has been unambiguously achieved with the aid of DFT/GIAO calculations.

Original publication

DOI

10.1021/jo3014947

Type

Journal article

Journal

J Org Chem

Publication Date

19/10/2012

Volume

77

Pages

9018 - 9028

Keywords

Acids, Benzopyrans, Catalysis, Crystallography, X-Ray, Magnetic Resonance Spectroscopy, Models, Molecular, Molecular Structure, Quantum Theory, Spiro Compounds