2‐Hydroxy‐1‐naphthaldehyde oxime was oxidized by AgO (or Ag₂O), in presence of N‐methyl morpholine N‐oxide (NMMO), to the title spiro adduct‐dimer (±)‐Spiro{naphthalene‐1(2H),4′‐(naphtho[2′,1′:2,3]pyrano[4,5‐c]furazan)}‐2‐one‐11′‐oxide by a Diels‐Alder(D−A) type self‐cycloaddition, through the agency of an o‐naphthoquinone nitrosomethide (o‐NQM). Moreover, 2‐hydroxy‐8‐methoxy‐1‐naphthaldehyde oxime was prepared and subjected to the same oxidation conditions. Its sterically guided result, 9‐methoxynaphtho[1,2‐d]isoxazole, was isolated, instead of the expected spiro adduct. The peri intramolecular H bonding in the oxime is considered to have a key contribution to the outcome. Geometry and energy features of the oxidant‐ and stereo‐guided selectivity of both oxidation outcomes have been explored by DFT, perturbation theory and coupled cluster calculations. The reaction free energy of the D−A intermolecular cycloaddition is calculated at −82.0 kcal/mol, indicating its predominance over the intramolecular cyclization of ca. −37.6 kcal/mol. The cycloaddition is facilitated by NMMO through dipolar interactions and hydrogen bonding with both metal complexes and o‐NQM. The 8(peri)‐OMe substitution of the reactant oxime sterically impedes formation of the spiro adduct, instead it undergoes a more facile cyclodehydration to the isoxazole structure by ca. 4.9 kcal/mol.

Naphtho[1,8-de][1,2]oxazin-4-ol and its acyl or benzyl derivatives ring open to various 2,8-dihydroxy-1-naphthonitriles, which, through (de)protection protocols and reduction, afford the target (E)-2-hydroxy-8-methoxy-1-naphthaldehyde. This was converted to its corresponding oxime, which was oxidatively o-cyclized with phenyliodine(III) diacetate (PIDA) to 9-methoxynaphtho[1,2-d]isoxazole 2-oxide. The latter, in deuterated DMSO at room temperature, was rearranged to its isomer 2-hydroxy-8-methoxy(naphthalen-1-yl)nitrile oxide. The isomerization was detected by time-course plot ¹H NMR spectroscopy and further identified from its ¹³C NMR and HRMS spectra. The nitrile oxide was stable in (non)deuterated DMSO for at least 18 h. A 3,4-bis(2-hydroxy-8-methoxynaphthalen-1-yl)-1,2,5-oxadiazole 2-oxide, as a dimerization product or an isocyanate as a rearrangement isomer, was ruled out, the former by its HRMS spectrum and the latter by its 1,3-dipolar cycloaddition reactions to substituted isoxazoles.

In this study, we considered the reaction of (E)-1-[(2-phenylhydrazono)methyl]naphthalen-2-ol with iodobenzene diacetate in dichloromethane-produced novel 3-phenyl-3H-naphtho[1,2-e][1,2,3]oxadiazine in 11% yield. By analogy to previously published work, we suggested that the reaction proceeds via the intermediacy of an o-naphthoquinone azomethide that undergoes conjugated 6π-electrocylization to produce the product. 1D, 2D NMR, HRMS, IR, and UV-VIS spectra provided information that supported the structure of the product.