Amidines are a class of oxoacid derivatives and used as Building Blocks in Synthesis
1. Amidines from nitriles
3-Cyanopyridine (52 g, 0.5 mol) was dissolved in MeOH (500 mL). Powdered NaOMe (2.7 g, 50 mmol) was added in one portion. The solution was stirred overnight at room temperature. After adding NH4Cl (30 g, 0.56 mol), the mixture was heated at reflux for 4 h and then cooled. The solvent was removed in vacuo. Absolute EtOH (600 mL) was added and the mixture was heated to reflux. After 15 min, the solids were filtered off and the mixture was allowed to cool to room temperature and stand overnight. Additional inorganic salts were filtered off, and the reaction mixture was concentrated to approximately 1/2 volume and filtered to afford 7.0 g of product (mp 186-188 oC). Concentration of the filtrate again to 1/2 its volume afforded an additional 25.0 g of product (mp 184-188 oC), followed by a third crop of 12.6 g (mp 184-188 oC) for a total of 44.6 g (57%) of 3-pyridinecarboximidamide.
2.Amidines from amides.
A solution of 0.1 mol of triethyloxonium fluoroborate in 50 ml of dry CHlCl2 was added to a suspension of 0.1 mol of the amide in 200 ml of dry CH2C12. The mixture was stirred overnight at room temperature. The solution was evaporated in Vacuo to one-third volume and treated with five volumes of anhydrous ether. The precipitated imidate fluoroborate was filtered and dried in uacuo. The salts could be recrystallized for analysis from dichloromethane or dichloromethane-ether. The crude salts were used in all cases for the amidine preparation. The imidate fluoroborate was stirred at room temperature in a tightly stoppered flrtsk with an 8-9% solution of ammonia or methylamine in absolute ethanol containing approximately a 40% excess of amine. After 3 days the mixture was evaporated to dryness in vacuo and treated with a small volume of water. The mixture was made strongly basic with 5 N NaOH and the insoluble oil was extracted into ethyl acetate or ether. The oil which remained after evaporation in vacuo of the organic solvent was either crystallized nnd purified or converted into the hydrochloride. A portion was also converted into the picrate.
3. Amidines from carboxylic acids
The following example is representative: PPSE was prepared from phosphorous pentoxide (1.42 g, 5 mmol) and hexamethyldisiloxane (2.56 g, 16 mmol) in 3 ml of CH2C12 at the refluxing temperature for 30 min, and the solvent was distilled away from the reaction mixture. To the residual syrup, p-methoxybenzoic acid (190 mg, 1.25 mmol) was added, and heated at 160 oC. After aniline (233 mg, 2.5 mmol) was added to the mixture, the solution was stirred at 160 oC for 5 h. The crude product was isolated by pouring the reaction mixture into 200 ml of cold 1M NaOH solution.
Recrystallization from aqueous ethanol gave pure N,N'-diphenylp-methoxybenzamidine melting at 115-116 oC (328 mg, 87%).
1. Synthesis of six-membered rings, such as Pyridines, Pyrimidines, Triazines and Tetrazines.
2.Synthesis of five-membered rings, such as Imidazole derivatives.
3. Synthesis of three-membered rings.
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