*2.2. Structure Determination*

The intermediates **3**–**8** were characterized by 1H- and 13C-NMR, IR, and HRMS. Compounds **1a** and **2a** were characterized by 1H-NMR. Phase-transfer catalysts **I**–**X** have been fully characterized. The structures of the thioureas **III** and **VI-Br** (the bromide analog of the compound **VI**) were determined by single-crystal X-ray analysis (Figure 2). In both structures, the *endo*-stereochemistry was confirmed at the C-2 chiral center. The conformational differences in the two structures in the solid state are shown in Figure 3. The main differences are due to the conformation of the benzyl group and the arylthiourea structural elements.

The *endo*-stereochemistry at the C-2 chiral center of compounds **III**–**X** was further confirmed by NOESY measurements based on the cross-peak between the methyl group and the *exo*-H(2) proton (Figure 4). Similarly, the *exo*-stereochemistry at the C-2 chiral center of compounds **I** and **II** was in line with the cross-peak between the methyl group and the *exo*-H–N proton observed in the NOESY spectra (Supplementary Materials).

**Figure 2.** Molecular structures of products **III** (**a**) and **VI-Br** (**b**). Thermal ellipsoids are shown at 50% probability.

**Figure 3.** Stick presentation of the superimposed molecular structures of products **III** (blue) and **VI-Br** (red).

**Figure 4.** The determination of stereochemistry at the C-2 chiral center of compounds **I**–**X** by NOESY experiments and the correlation between the multiplicity of the H–C(3)-*endo* proton (He) and the *endo* absolute configuration at the C-2 chiral center of compounds **1**, **3**, **5**, **7**, and **III**–**X** (Supplementary Materials).

Finally, the stereochemistry at the C-2 chiral center can be correlated on the basis of the multiplicity of the H–C(3)-*endo* proton (He) (Figure 4). Exclusively in the *endo*-isomes of compounds **1, 3**, **5**, **7**, and **III**–**X**, the H–C(3)-*endo* proton appears as a doublet of doublet between 0.67 and 1.35 ppm (Table S7 in Supplementary Materials).
