Recently, we reported a Lewis acid-catalyzed [4π + 2σ] cycloaddition of BCBs with nitrones, providing the novel hetero-BCHeps. Hence, we speculated that the intended spiro-BCHs may also be achieved via the Lewis acid catalyzed dipolar cycloaddition of BCBs with particular 2π-partners. The benzofuran-derived oxa(aza)dienes, which were widely utilized in the synthesis of the important benzofuran-incorporated heterocycles, may serve as the ideal choice for constructing desired spiro-BCHs which incorporated the potentially bioactive benzofuran units. To realize the transformation, several issues should be concerned. It is noteworthy that the Lewis acid catalyzed dipolar cycloadditions of BCBs with α,β-unsaturated compounds have not been reported, which presumably caused by the mismatch between in-situ formed BCB-dipole and 2π-partner. Consequently, choosing either a suitable Lewis acid catalyzed system and 2π-partner is crucial in matching the reactivity of BCB dipoles and electron-deficient oxa(aza)dienes. Besides, the Lewis acid catalyzed dipolar [2π + 2σ] reactions of BCBs with imines or ketones have been realized by Leitch and Glorius , indicating the imine or ketone units of oxa(aza)dienes may react with BCBs which leading to complex chemoselectivity in the reaction. We inferred that this pathway is unfavored due to the potential aromatization driving force of benzofuran-derived oxa(aza)dienes (path a), although this property also may lead to the generation of undesired [4π + 2σ] product (path c). Additionally, the formation of cyclobutenes from BCBs is also a potential side reaction and needs to be inhibited. Herein, we report a formal [2π + 2σ] cycloaddition of BCBs with benzofuran-derived oxa(aza)dienes promoted by Lewis acids, providing a series of novel spiro-BCHs with a broad substrate scope (Scheme 2).