Naphthoxide ions benzylation

The alkylation of sodium 2-naphthoxide with benzyl bromide in tetrabutylam-monium and tetrabutylphosphonium halide salts was investigated by Brunet and Badri [50] (Scheme 5.1-21). The yields in this reaction were quantitative, and alkylation occurred predominantly on the oxygen atom of the naphthoxide ion (typically 93-97 %). The rate of the reaction was slower in the chloride salts, due to the benzyl bromide reacting with chloride ion to give the less reactive benzyl chloride. 

Kornblum et al. (1963) demonstrated that O- vs. C-alkylation (24) of yS-naphthoxide ion (an ambident ion) is markedly solvent dependent. For example, the reaction with benzyl bromide conducted in dimethylformamide gave 97% O-alkylated product, whereas in water 81% C-alkylated product resulted. The difference is attributed to changes in the solvation of ambident anions. The course of the reaction is also influenced by water concentration in... 

Not all nucleophilic displacement reactions require lightly substituted onium ion catalysts for activity. For alkylation of 2-naphthoxide ion with benzyl bromide (Eq. (6)) 40-100% RS, 2% CL polystyrene catalysts 15 and 16 work well54). A 51 % RS catalyst 11 gave good yields in reactions of anionic oxygen and sulfur nucleophiles with alkyl halides 91). 

Alkylation of 2-naphthoxide ion (Eq. (6)) occurs mainly on carbon in aqueous solvents and mainly on oxygen in aprotic solvents. The product distribution is often used as a probe of the solvent environment in heterogeneous reactions. Brown and Jenkins 54) found that 40-100 % RS spacer chain catalysts 15 and 16 gave up to 98 % O-benzylation of 2-naphthoxide ion with benzyl bromide. The shorter spacer chain catalyst 16 gave 85% O-alkylation, and a conventional benzyltrimethylammonium ion resin 2 gave about 70 % O-alkylation. Because of low activity, product distribution data were obtained with varied amounts of catalyst and were extrapolated to equimolar amounts of catalyst and substrate to obtain the catalyzed O/C product ratios. Interpretation of the data also was complicated by independent evidence that catalysts 15 adsorbed 2-naphthoxide ion, in addition to that bound by ion exchange54). Essentially the same results were obtained with catalysts 24 which lack the ester link in the spacer chain 106). 

The first attempts to use macroporous polystyrene supports for onium ion catalysts were reported in the early papers of Brown and Jenkins 54) and of Regen 89). The lightly cross-linked macroporous Rohm and Haas XE-305, 46 % RS as spacer chain catalyst 15, gave O- and C-alkyl products from 2-naphthoxide ion and benzyl bromide... 

Low percent ring substitution is not critical for activity in all nucleophilic displacements. Brown and Jenkins found 40% to 100% ring substituted catalysts highly active for 0-alkylation of 2-naphthoxide ion with benzyl bromide. 

Brown and Jenkins found that 98% ring substituted catalyst gave 98% 0-benzylation of 2-naphthoxide ion, and that catalyst (2% cross-linked, >90% substituted) gave about 65% 0-benzyl product (eq 5). The long aliphatic spacer chain creates a more hydrophobic... 

---