We began our study by investigating the photochemical [2+2]-cycloaddition reaction, employing an energy transfer process from an excited state sensitizer, Ir.cat, to gem-diborylatedalkenes 1 (Figure ). To validate our proposal, we chose gem-diborylphenyl alkene 1a and styrene 2a as model substrates for this reaction (Figure ). After an exhaustive screening process, we successfully identified the optimal reaction conditions. These conditions involved the utilization of the fac-Ir(ppy) 3 catalytic system and 1,2-dichloroethane (DCE) as a suitable solvent. The reaction mixture was then exposed to a 450 nm blue LED for 48 hours (further details can be found in the supporting information on pages S16-17). Fortunately, the desired product gem-(Bpin,Bpin)cyclobutane 3a was successfully obtained as the exclusive regioisomer in 82% yield. Of note, cyclobutane product 3a was formed with diastereoselectivity of 1.17:1, however, it is worth noting that both cyclobutanediastereomers (syn-3a and anti-3a) could be easily separated via column chromatography, representing a significant advantage in our study (Figure ). The relative structures of both cyclobutane diastereomers of 3a were conclusively determined through X-ray crystallographic analysis (please refer to Figure for the X-ray structures of syn-3a and anti-3a). These structures indicate that the new C-C bonds are forming regioselectivity in the way that the coupling occurs between the gem-diborylated carbon position (in I) to the less steric side of the olefin 2 as proposed pathway of the reaction from on Figure , following by construct the four memberedring via radical-radical cross-coupling of I-3. Notably, in the absence of photocatalyst and light, the reaction did not proceed; this control experiments confirmed the essential roles of the Ir-sensitizer and the blue LED for the successful EnT process. Furthermore, when the [2+2]-cycloaddition reaction was carried out using the standard reaction conditions in the presence of TEMPO, it resulted in no observable reaction. This observation might support the possibility of a radical mechanism being involved in the reaction. The scope of the reaction. The relative structure of syn-3a and anti-3b were confirmed by X-ray crystallography and for others the relative syn-and anti-configuration were determined by 2D-NMR NOESY studies (please see Supporting Information for more details). The dr (anti:syn) = diastereomeric ratio of 3a-j was determined by crude 1 H-NMR. Of note: diastereoisomers (anti and syn) of products 3a-j were isolated separately by column. Bpin = pinacolato-boron, DCE = 1,2-Dichloroethane. fac-Ir(ppy) 3 is fac-Tris(2-phenylpyridine)iridium(III). r.r. = regioselectivity ratio. Yields of isolated products are given.