pathways initiated by photoinduced energy transfer, single-electron transfer process. There is still insufficient research on the reaction process of two-electron reaction process for BCBs. In this context, development of a new approach to construct BCHs with enol silyl ethers and BCBs involving two-electron reaction process promoted by commercially available Lewis acid catalysis is established, providing a series of BCHs with polycyclic structures. It is worth mentioning that after completing the racemic work, when we attempted the chiral version of this reaction, a similar work from Deng's group had just been published in ChemRxiv. Inspired by the excellent researches mentioned above, we hypothesize to develop a new method for intermolecular formal [2π+2σ] cycloaddition of enol silyl ethers with bicyclo[1.1.0]butanes via strain-release promoted by Lewis acids catalysis. Based on these considerations, we selected BCBs 1a with electron-rich cyclic enol silyl ether 2a as model substrates in the presence of 10 mol % of Fe(OTf)2 in DCM at at room temperature in dark as shown in table 1. To our surprise, the intermolecular formal [2π+2σ] cycloaddition product 3a was obtained in 45% yield (Table , entry 1). Next, in order to increase the ability of Lewis acid to activate substrates, an extensive screening of Lewis acids for their ability to promote the reaction of cyclic enol silyl ether 2a and BCB 1a was conducted (entries 2-10). When Fe(OTf)3, AgOTf, Cu(OTf)2 or Sc(OTf)3 are used as Lewis acid catalysts for the reaction, the products 3a was almost unavailable. Further investigations of a variety of metal triflates or biflates including Zn(OTf)2 ,Y(OTf)3, La(OTf)3, Ni(OTf)2 and Yb(OTf)3 identified Yb(OTf)3 as the best catalyst. Increasing the catalyst Yb(OTf)3 loading to 20 mol% under standard reaction conditions, the products 3a was acquired with a slightly higher yield (Table , entry 11). Moreever, screening of solvents in the presence of 10 mol % of Yb(OTf)3 revealed C6H5Cl as the optimal solvent. Finally, increasing the amount of catalyst Yb(OTf)3 to 20% resulted in an 85% yield. The reaction could not afford any product in the absence of Yb(OTf)3 (entry 18). With the optimized reaction conditions in hand, a variety of cyclic enol silyl ethers or acyclic enol silyl ethers with BCBs were employed to test the generality of intermolecular formal [2π+2σ] cycloaddition process as described in Scheme 2. Initially, the 1-tetralone derivatives 2b-2c, 2e and 2g with electron withdrawing groups 7-chloro, 7-bromo 7-nitro and 5-bromo substituents reacted with 1a to afford the corresponding adducts 3b-3c, 3e and 3g in 25-61% yields. The results indicated that strong electron withdrawing groups in the benzene ring reduced reaction activity. Benzene-fused substrates with 5-OMe and 7-OMe substituents (2d, 2f) were tolerated well under the standard reaction conditions, giving cycloaddition products 3d and 3f in 52-58% yields. When the 3,4-dihydronaphthalen-1-one derived cyclic enol silyl ether with -OTs and methyl substituents 2h and 2i were used, the products 3h and 3i were obtained with 56%-63% yields. Aside from naphthyl ketones, other aromatic ketones were generally compatible, affording the products 3a'-3c' in 31-49% yields. 1-Indanone-derived pentacyclic silyl enol ethers (4a-4i), and different substitution patterns such as 5 or 6-fluoro, 4 or 6-chloro, 4 or 6-bromo and 4 or 6-methoxyl substituents are tolerated under the standard reaction conditions, affording 5a-5i in 31-81% yields. Besides, 1-indanone-derived pentacyclic silyl enol ether (4j) with methyl substituent reacted with BCBs 1a providing BCHs 5j containing quaternary carbon centers. Monocyclic enol silyl ethers were also tested. To our delight, five-, six-and seven membered-ring substrates (6a-6c) proceeded smoothly under the standard conditions achieving poor yields (16-35% yields). Furthermore, a variety of acyclic silyl enol ethers were employed to test the generality of this intermolecular formal [2π+2σ] cycloaddition with bicyclo[1.1.0]butanes. Initially, acyclic silyl enol ethers with electron-donating substituted phenyl ring were evaluated, and in all case (9a-9d) in 41-83% yields were achieved. Acyclic silyl enol ether bearing 1-naphthyl could afford the desired product 9e with 75% yield. Notably, acyclic tri-substituted silyl enol ethers is viable substrate, allowing the rapid construction of highly substituted and compact bicycles 9f in 59% yield with high diastereoselectivity (20:1 dr). In addition, when BCBs contained structures such as Weinreb amide, ester and cyclic enol silyl ethers with sulfur-containing atoms, the reaction did not proceed smoothly. Furthermore, Compounds with tert butyl due to large steric hindrance substituent could not react.