Effect of conditions and substrate structure in the synthesis of MAC rotaxanes 4. Previously, we found that the AT-CuAAC reaction of azide (R)-1a, macrocycle 2, and alkyne 3 gave rotaxanes (Rma,Rco-c) 18 -4a (major) and (Sma,Rco-c)-4a (minor), which have the same static co-conformational covalent configuration (set by the configuration of 1a and static because the NHBoc unit is too large to allow shuttling) and opposite mechanical axial configuration, in 50% de (Scheme 1; Table , entry 1). The solid-state structure obtained by single crystal x-ray diffraction (SCXRD) of an analogous catenane 11 contained a close contact between the polarized NH of the carbamate unit and the O atom of the sulfoxide unit, which suggested that an H-bond between these groups may play a role in the observed stereoselectivity. 19 Scheme 1. Synthesis of rotaxanes 4 a a Reagents and conditions (see also Table ): (R)-1 (1.1 equiv.), 2 (1 equiv.), 3 (1.1 equiv.), [Cu(CH3CN)4]PF6 (0.96 equiv.), i Pr2NEt (2 equiv.). b Determined by SCXRD for 1a