Benzamidomethylation with (Benzamidomethyl)triethylammonium Chloride. 2. A Simple Method for Benzamidomethylation of Thiols, Amines and

Abstract: Thiols and amines were benzamidomethylated in water solution at room tem-perature with (benzamidomethyl)triethylammonium chloride ( 1 ) in the presence of a smallquantity of triethylamine (pH>9). Benzamidomethyl thioethers ( 3a - d ) and (benzami-domethyl)amines or di(benzamidomethyl)amines ( 5 ) were obtained in high yields (>90%) aswell as S(CH 2 NHBz) 2 in a reaction of 1 with Na 2 S. Benzamidomethyl estersRCOOCH 2 NHBz were obtained (60-75%) in reactions of carboxylic acids with 1 in chloro-form or dioxane. Keywords: Benzamidomethylation, thiols, carboxylic acids, amines. Introduction In the past, a large number of benzamidomethyl compounds have been synthesized which have beenused for different purposes. In the final decade, in the case of a thiol group, benzamidomethylation wasused for synthesis of ligands for 99 Tc complexes, which have been utilized as radiolabels [2-4]. Also,benzamidomethylation was used to obtain some benzamidomethyl aryl thioethers as intermediates inthe synthesis of benzothiazines [5-7]. Among the numerous


Introduction
In the past, a large number of benzamidomethyl compounds have been synthesized which have been used for different purposes.In the final decade, in the case of a thiol group, benzamidomethylation was used for synthesis of ligands for 99 Tc complexes, which have been utilized as radiolabels [2][3][4].Also, benzamidomethylation was used to obtain some benzamidomethyl aryl thioethers as intermediates in the synthesis of benzothiazines [5][6][7].Among the numerous S-benzamidomethyl derivatives there are reports of a S-benzamidomethyl-L-cysteine, which was used in peptide synthesis [8][9][10][11] and some of them are useful for the treatment of glaucoma [12].Also, wool proteins can be analyzed as the corresponding S-amidomethyl derivatives [13].Amidomethyl and benzamidomethyl esters were synthesized and evaluated as potential prodrugs of carboxylic acid agents [14][15][16][17] or amide agents [18].The benzamidomethyl esters of carboxylic acids were used as a benzamidomethylation regent for compounds with a different nucleophilic group [19,20].In the case of an amine group, amidomethylation was used for synthesis of derivatives of some uracils or thiouracils that showed antitumor activity [21,22].Zlotin and coworkers [23] investigated some routes for the synthesis of N-benzamidomethyl derivatives of functional derivatives of α-aminoacids and peptides, etc.Our good results with the benzamidomethylation of phenols [1] using (benzamidomethyl)triethylammonium chloride (1), prompted us to investigate the reaction of this compound with thiols, carboxylic acids and amines.

Results and Discussion
Reactions with thiols were performed in very vigorously stirred aqueous mixtures of 1 and thiols 2(a, b, c and d), in the presence of a small quantity of triethylamine (TEA) to pH>9 (Scheme 1).The reactions with liquid thiols (2a,c,d) in the first 5-10 minutes gave yellow oils which over the next 5-10 minutes are transformed to small white solid lumps.For best results, the lumps should be ground with a glass rod and the reaction mixture stirred over 1 hour, although in same cases the reaction is over in 30-40 minutes.The products were collected by filtration.The sparingly water soluble 2-thionaphtole (2b) was also benzamidomethylated with 1, but the reaction mixture was stirred over 3 hours.Reactions of 1 with aqueous solutions of Na 2 S always gave dibenzamidomethyl sulphide (3e; R = CH 2 NHBz, Y = S), regardless of the mole ratio of reactants (compound 1 : Na 2 S = 1:0.5;1:1; 1:2 or 1:5).An attempt to synthesize N-(sulphonylmethyl)benzamide (PhCONHCH 2 SH) at pH = 9 (where the concentration of S 2-ions is minimal and concentration of SH - ions is maximal [24]) failed.Under these conditions the reaction did not occur.An experiment with and aqueous solution of H 2 S and controlled increase of pH failed, too.The reaction started and occurred rapidly only when the pH of the mixture was ~10 and higher; however only 3e was obtained.Product 3e was also obtained in the reactions of 1 with thioacetic acid and thioacetamide.However, in a reaction of ammonium pyrroldinedithiocarbamate (2f) with 1, performed in aqueous solution (at room temperature), benzamidomethyl pyrroldinedithiocarbamate (3f) was obtained.
The benzamidomethylation reactions of carboxylic acids with 1 did not take place in aqueous solutions.Benzamidomethyl esters 3(g,h) were obtained in the reactions of carboxylic acids 2(g,h) and 1, performed for 20 min in boiling chloroform in the presence of a small quantity of TEA.Benzamidomethylation of 2i (which is sparingly soluble in chloroform) under the same conditions did not give good results.But, when the reaction was performed in a dioxane suspension of 1, benzamidomethyl hippurate (3i) was obtained in more than a 70% yield.The temperature of the mixture had to be higher than 40 o C (at lower temperatures, the reaction does not occur or is very slow) and lower than 60 o C (otherwise, a branching reaction occurs, and N,N'-methylenedibenzamide is obtained).Under the same conditions 3f and 3g were also obtained. 1H-NMR and 13 C-NMR data of compounds 3a-i are given in Table 1, and physicochemical data are given in Table 2.
Benzamidomethylation of amines in the aqueous solutions occurred immediately (Scheme 2).At room temperature 1 reacts very quickly with the primary amines (4a-c) as well as with the secondary amine (4e).Because of that, dibenzamidomethyl derivatives of primary amines (5a-c) were obtained regardless of whether the reaction mixture had a larger quantity of primary amine than of 1.For the synthesis of monobenzamidomethyl derivative of aniline (5d), drops of a very dispersed water solution of 1 had to be added to a very concentrated and vigorously stirred aqueous solution of aniline (4c).Benzamidomethylation of sparingly water soluble diphenylamine (4f) was performed in dioxane-water mixture as a solvent.The reaction of 1 with an aqueous solution of NH 3 gave a mixture of di(benzamidomethyl)amine (5g) and tri(benzamidomethyl)amine (5h).The major component (5g; 50-70%) was obtained when small quantities of 1 in powder form were added to a vigorously stirred large volume of 37% aqueous solution of NH 3 .Compound 5h was obtained without admixture of 5g when aqueous NH 3 was dropped into a concentrated aqueous solution of 1. Also, 5g formed when a large quantity of TEA was added to the aqueous reaction mixture of 1 or an aqueous mixture of 1 and any other nucleophilic substrate (phenols, thiols, etc).A possible explanation for this phenomena is that pure TEA (98%) contains some quantity of NH 3 .The physicochemical data of compounds 5a-h are given in Table 2, and their 1 H-NMR and 13 C-NMR data are given in Table 3.

Conclusions
In conclusion, compound 1 is an excellent benzamidomethylation agent for thiols and amines and a good agent for carboxylic acids.Reactions of 1 with thiols and amines occurred faster and with higher yields (>90%) than the reactions of 1 with phenols, at room temperature.The products are easily isolated from reaction mixture by simple filtration.

Benzamidomethyl phenyl sulphide (3a)
A solution of 1 (2.8611 g, 10.59 mmol) in water (40 cm 3 ) was added to the water (40 cm 3 ) mixture of 2a (0.538 g, 5.7 mmol) and TEA (0.3-0.5 cm 3 ).The mixture was stirred for 1h at room temperature.White lumps formed, which were ground with a glass rod.Colorless crystals were collected by filtration.Purification was performed by dissolving the product in cold EtOH (the smallest quantity possible) and precipitating with drops of cold water.
3b, 3c, 3d and 3f were synthesized in a similar manner as 3a, and only the differences are noted for each product.

Benzamidomethyl benzyl sulphide (3c)
Colorless crystals; Purification was performed by dissolving the product in cold acetone (smallest quantity possible) and precipitating with drops of cold water.

Benzamidomethyl pyrroldinedithiocarbamate (3f)
Gray-white crystals; The purification was performed by dissolving the product in dioxane and precipitating with drops of cold water.

Benzamidomethyl benzoate (3g)
Mixture of 1 (2.5633 g, 9.46 mmol), 2g (0.9758 g, 7.99 mmol) and TEA (0.2-0.4 cm 3 ) in CHCl 3 (40 cm 3 ) was refluxed for 20-30 min.The solvent was removed under reduced pressure and theresidue was dissolved in dioxane.After filtration, water was added to the dioxane solution until a white precipitate appeared.Colorless crystals were filtered and purified by repeating the last procedure.Compound 3g was also synthesized as described for 3i.

Benzamidomethyl hippurate (3i)
To a suspension of 1 (2.122 g, 7.83 mmol) in dioxane (40 mL) was added hippuric acid (2i) (1.020 g, 5.69 mmol) and TEA (0.2-0.4 cm 3 ).The mixture was stirred and heated at 50 o C for 24 h.After cooling, water was added to the mixture until a white precipitate appeared.Colorless crystals were filtered and purified as for 3g.

Di(benzamidomethyl)amine (5g)
Powdered 1 (2.1769 g, 8.04 mmol) was added with spatula in small portions to the vigorously stirred 37% aqueous solution of NH 3 (60 cm 3 ).After 20 min, the precipitate formed was filtered off and dissolved in a small quantity of acetone.The solution was filtered to remove the admixture of 5h.Colorless crystals of 5g were obtained by precipitation with water.5b, 5c, 5e and 5h were synthesized in a similar manner as 5a, and only the differences are presented for each product.

Table 1 .
NMR data of compounds 3a-i.

Table 2 .
Physicochemical data of compounds 3a-i and 5a-h.