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Treatment of 1,4-dibromo-2,5-dimethoxybenzene (6) with NaNH 2 followed by 1,1-dimethoxyethene (7) afforded the biand tricyclic acetals such as 8 and 9 as the products of [2+2] cycloadditions of the intermediate arynes. After chromatographic separation and acetal hydrolysis the title compounds 15 and 16 were obtained in high yields as the first represen-

Based on sequential organic transformations, that is, diimine formation, Staudinger [2 + 2] ketene–imine cycloaddition, and ring-closing metathesis (RCM) reactions, the synthesis with full structural identification including NMR and HRMS spectral data along with single X-ray diffraction analysis (for anti 7b, anti 8b, syn 9a, and anti 9b) of the first syn/anti bis-4-spiro-β-lactams-based azacrown ethers (7a,b–9a,b) is reported.