Regiochemistry of Twofold Additions to [6,6] Bonds in C60: Influence of the Addend‐Independent Cage Distortion in 1,2‐Monoadducts

Three series of regioisomeric bisadducts of C60, namely, C62(anisyl)4 and the mixed systems C62(anisyl)2‐(COOEt)2, and C61(COOEt)2(NCOOEt), were synthesized starting from the 1,2‐monoadducts C61(COOEt)2 (1), C61‐(anisyl)2 (2), and C60(NCOOEt) (4) by using the Bingel and Bamford‐Stevens reactions, and nitrene additions. In the case of C61(COOEt)2(NCOOEt) the complete series of nine possible regioisomers were isolated for the first time. For steric reasons the cis‐1 isomers of C62(anisyl)4 and C62(anisyl)2(COOEt)2 were not formed. The transannular [6,6] bonds in the cis‐1 isomer 42 of C61(COOEt)2(NCOOEt) are closed. The properties and regioselectivities of formation of these bisadducts and their monoadduct precursors were compared with those of the series C62‐(COOEt)4 and C60(NCOOEt)2, which we synthesized previously. In the additions to 1, 2, and 4 the preferred positions of attack are e and trans‐3 for sterically demanding addends (e.g., combinations of C(anisyl)2 and C(COOEt)2) and cis‐1, e, and trans‐3 for sterically less demanding addends (e.g., combinations of N(COOEt) and C(COOEt)2). A detailed analysis of the MO structures, the experimental and calculated geometries of monoadduct precursors, and the stabilities of reaction products leads to the conclusion that the addend‐independent cage distortion itself is responsible for the observed regioselectivities of bisadduct formations.