**2. Results and Discussion**

## *2.1. Synthesis*

Camphor-derived *endo*-diamines **1a**,**b** and *exo*-diamines **2a** were prepared in four steps from commercially available (1*S*)-(+)-10-camphorsulfonic acid (Scheme 1) [29,30]. Camphorsulfonic acid was transformed into 10-iodocamphor in an Apple-type reaction, followed by nucleophilic substitution with pyrrolidine or dimethylamine in dimethyl sulfoxide. The thus formed tertiary amines were transformed into the corresponding

oximes. The final oxime reduction with sodium in isopropanol gave a mixture of the corresponding major *endo*-diamines **1a**,**b** and minor *exo*-diamines **2a**, separable by column chromatography.

**Scheme 1.** Synthesis of camphor-derived *endo*- **7a**,**b** and *exo*-quaternary ammonium salts **8a**.

Next, the primary amino group of diamines **1a**,**b** and **2a** was Boc-protected, yielding **3a**,**b** and **4a**, respectively. In the following step, we introduced the benzyl group to the tertiary amine (benzyl groups have been very successfully established as useful motives for numerous quaternary ammonium salt phase-transfer catalysts [4–8]). Alkylation with benzyl bromide thus gave the quaternary ammonium salts **5a**,**b** and **6a**. Potassium carbonate was added to ensure complete conversion. They were subsequently Boc-deprotected with trifluoroacetic acid or aqueous hydrogen iodide, furnishing ammonium salts **7a**,**b** and **8a**, respectively (Scheme 1).

Finally, the ammonium salts **7a**,**b** and **8a** were reacted with aromatic iso(thio)cyanates **9** and squaramate **10** to give the quaternary trifluoroacetate ammonium salts **I**, **IV**, **VI**, **VII**, and **IX**. The quaternary iodide ammonium salts **II**, **V**, and **VIII** were formed from the corresponding trifluoroacetates **I**, **IV**, and **VII**, respectively, via anion metathesis with excess NaI in dichloromethane (Scheme 2). The quaternary iodide ammonium salts **III** and **X** were formed directly from the iodide ammonium salt **7b** and the corresponding isothiocyanate. The catalysts thus formed have either (thio)urea or squaramide hydrogen bond donors (Supplementary Materials).

**Scheme 2.** Synthesis of camphor-derived phase-transfer organocatalysts.
