In recent decades, the development of methods for constructing conformationally constrained three-dimensional (3D) molecular structures has attracted considerable attention, particularly in light of the success of the "escape from flatland" concept proposed by Lovering, who advocated using three-dimensional saturated carbon rings instead of planar benzene rings in drug discovery. C(sp 3 )-rich cyclic scaffolds possess rigid conformations and metabolic stability, which may improve the pharmacokinetic and physicochemical properties of lead compounds. For example, the related bicyclo [2.1.1]hexane (BCH) and oxygen-or nitrogen-containing bicyclo[2.1.1]hexane (XBCH) have been proposed as potential bioisosteres for ortho-and meta-substituted benzene and pyrrolidine, respectively. In addition, bicyclo [1.1.1]pentane (BCP) and bicyclo [3.1.1]heptane (BCHep) derivatives have been successfully used as mimics for para-and meta-substituted benzene, respectively. Notably, the design and synthesis of BCH or BCP have garnered widespread attention via [2+3], [1+3], [3+3], [4+3] and [5+3] 18 cycloaddition reactions including a single-electron transfer process, triplet energy transfer, pyridine-boryl radical catalysis, CPA-photoredox reaction, a two-electron reaction process, and so on. However, to the best of our knowledge, the [8+3] cycloaddition employing azaheptafulvenes and BCBs has not been developed so far. In conjunction with our ongoing efforts in BCBs cycloaddition chemistry, we envisioned that the [8+3] cycloaddition reactions were carried out with azaheptafulvenes and BCBs via Lewis acid catalysis. In this paper, we report an asymmetric [8+3] cycloaddition reaction between azaheptafulvenes and BCBs catalyzed by FeCl3 or Sc(OTf)3, providing an efficient and straightforward method for the synthesis of Nitrogen-containing polycyclic compounds. As shown in table 1, we selected BCB 1a with azaheptafulvene 2a as model substrates in the presence of 10 mol % of Yb(OTf)3 in DCM at room temperature. To our surprise, the intermolecular formal [8+3] cycloaddition product 3a was obtained in 37% yield (Table , entry 1). Next, in order to increase the ability of Lewis acid to activate substrates, a wide screening of Lewis acid promoted azaheptafulvene 2a and BCB 1a was conducted (entries 2-11). When Sc(OTf)3, Cu(OTf)2, Fe(OTf)3, AgOTf or Y(OTf)3 are used as Lewis acid catalysts for the reaction, the products 3a was almost available with Sc(OTf)3, Cu(OTf)2, Fe(OTf)3 or Y(OTf)3. Among them, under the catalysis of Sc(OTf)3, 3a achieved up to 64% yield. Further investigations of a variety of Lewis acids including Zn(OTf)2, BF3 . Et2O, TMSOTf, Fe(OTf)2 and FeCl3 identified FeCl3 as the better catalyst almost the same as Sc(OTf)3 with 65% yield. Moreover, screening of solvents in the presence of 10 mol % of FeCl3 revealed Xylene as the optimal solvent with 69% yield. The reaction could not afford any product in the absence of FeCl3 (entry 22). Finally, by adjusting the proportion of reaction substrates and increasing the catalyst FeCl3 loading, a yield of 92% could be obtained for 3a (entry 23). Notably, a yield of 90% could be obtained for 3a under the 10 mol % of Sc(OTf)3 (entry 24). The above experimental results indicated that both Lewis acids FeCl3 and Sc(OTf)3 could achieve good yields and diastereoselectivity. With the optimized reaction conditions in hand (Lewis acids FeCl3 or Sc(OTf)3 as catalyst), a variety of azaheptafulvenes with BCBs were employed to test the generality of intermolecular formal [8+3] cycloaddition process as described in Scheme 2. Initially, we tried different electron-donating groups of azaheptafulvenes, such as Me, Et or t Bu, and we obtained products 3a-3c and 3i in 83-92%/75-90% yields. 3d was obtained with 89%/75% yield with N-PhSO2 of azaheptafulvene. The azaheptafulvenes 2e-2h and 2j with electron withdrawing groups 4-fluoro, 2-fluoro, 4-nitro 4-CF3 and 4-CN substituents reacted with 1a to afford the corresponding adducts 3e-3h and 3j and 3k in 42-91%/29-86%yields. The results indicated that strong electron withdrawing groups in the benzene ring reduced reaction activity. In addition, moderate yields (3l-3n, 60-66%/52-58% yields) could still be obtained when polyfluorosubstituents were placed at different positions on the benzene ring of azaheptafulvenes. 2-Naphthone of BCBs can be replaced with n-pentanone, and moderate yields can be obtained for both electron-donating and electron-withdrawing groups on the benzene ring (3o-3s, 48-88%/35-73% yields). When the nitrogen substituent is 2-naphthyl, 3t achieves a good yield (3t, 71%/63% yield). 2-Naphthone of BCBs can be replaced with 2-benzothiophenone, and moderate yields can be obtained for 3u (3u, 86%/74% yield). Finally, substrates from 1-0 to 9-0 could not successfully obtain cycloaddition products.