## Introduction
### Results and Discussion
In addition, toluene was used as solvent and 25% aq NaOH as base when working at r.t. or 0\({}^{\circ}\)C, whereas a mixture of toluene/CHCl\({}_{3}\) (7:3 v/v) and 50% aq KOH was used when lower reaction temperatures were employed [8c]. The resulting yields and _ee's_ are summarized in Table 1. In all cases the (_S_)-enantiomer **20** was obtained. The _ee_ values were determined by chiral GLC analysis from the corresponding trifluoroacetamide, obtained after 2M HCl hydrolysis of the imine **20** and further reaction with trifluoroacetic anhydride [29]. A racemic reference sample of **20** was prepared using tetrabutylammonium bromide as phase-transfer catalyst. **Scheme 3. **  
From the results shown in Table 1 it can be observed that the Merrifield-anchored cinchonidine-derived ammonium salt **2a** afforded the higher _ee_ at 0\({}^{\circ}\)C (90%, Table 1, entry 2), and lowering the reaction temperature further did not produce an increase in the _ee_ (entries 3 and 4). However, its allylated counterpart **2b** gave place to considerably lower _ee_ values, both at r.t. (entry 5) or 0\({}^{\circ}\)C (entry 6). The analogous polymeric quinine derivative **2c** was clearly less effective as an asymmetric PTC catalyst than its structurally similar cinchonidine-derivative **2a**, giving very low _ee_'s (Table 1, entries 7 and 8). Moreover, the (1\(R\),2_S_)-_N_-methylepherdrine-derived resin **9** gave a low yield of an almost racemic **20** (Table 1, entry 9). The polymeric trityl-anchored cinchonidine salt **10a** gave a 44% _ee_ of **20** working at r.t. (Table 1, entry 10), which was raised to 70% _ee_ when the temperature was lowered to 0\({}^{\circ}\)C (Table 1, entry 11), but showed no further increment when the reaction was carried out at -20\({}^{\circ}\)C (Table 1, entry 12). Similarly to **2a**, when the benzylation reaction was carried out with the _O_-allylated trityl-supported resin **10b** resin, the _ee_ dropped remarkably (Table 1, entry 13). In addition, the JandaJelTM-anchored cinchonidine ammonium salt **11** gave a 62% _ee_ of **20** at r.t. (Table 1, entry 14) and a slightly lower 56% _ee_ at 0\({}^{\circ}\)C, with an observed increase of the reaction time (Table 1, entry 15), whereas the Wang-supported cinchonidinium salt **12** gave _ca._ 55% _ee_, both at r.t. or 0\({}^{\circ}\)C (Table 1, entries 16 and 17). Moreover, ArgoGelTM-supported cinchonidinium salt **13a** afforded up to 68% _ee_ from r.t. to -20\({}^{\circ}\)C (Table 1, entries 18-20) and again a tremendous drop in the _ee_ was observed using its _O_-allylated counterpart **13b** (Table 1, entry 21). Furthermore, when the _N_-substituted 9-anthrylmethyl derivative **16** was used as PTC catalyst, up to 74% _ee_ of **20** was obtained working at -20\({}^{\circ}\)C (Table 1, entry 23). The use of the co-polymeric cinchonidinium ammonium salt **18** with an anthrylmethyl group at the N gave a 44% _ee_ when working at r.t. (Table 1, entry 25), which increased to 70% \(ee\), almost independently of reductions in the temperature to 0\({}^{\circ}\)C or -20\({}^{\circ}\)C (Table 1, entries 26 and 27). After the benzylation reaction, the polymeric catalysts were filtered off from the reaction mixture and were reused up to three times without any loss of effectivity. \begin{table}
\begin{tabular}{c c c c c c c c} \hline Entry & Catalyst & Base & Solvent & T (\({}^{\circ}\)C) & t (h) & Yield\({}^{\mathrm{a}}\) (\%) & \(ee^{\mathrm{b}}\) (\%) \\ \hline  
OH & PhMe:CHCl\({}_{3}\) & -20 & 13 & 74 & 71 \\ \hline \end{tabular}  
* Crude yield determined by \({}^{1}\)H NMR (300 MHz). \({}^{\mathrm{b}}\) Determined by chiral GLC analysis from the corresponding trifluoracetamide (see text).  
\end{table} 
Table 1: Enantioselective PTC benzylation of glycine derivative **19** using polymeric chiral catalysts