Imidazoles manganese dioxide

Synthesis of imidazole-2-carboxaldehyde has previously been reported by manganese dioxide oxidation of the corresponding car-binol,4 by acid-promoted cyclization of 7V-(2,2-diethoxyethyl)-2,2-... 

The specific synthesis of 1,4- and 1,5-disubstituted imidazoles in 70% yields has been achieved by cyclizing 2-amino-3-methylaminopropionic acid with triethyl orthoformate. The products are isolated after dehydrogenation with active manganese dioxide of the 2-imidazoline (69 Scheme 37) (70AHC(12)103). 

A specific synthesis of 1,4- and 1,5-disubstituted imidazoles has been accomplished in about 70% yields by cyclization of 2-amino-3-methylaminopropanoic acid and 3-amino-2-methylaminopropanoic acid, respectively, with tricthyl orthoformate (Scheme 3.1.2). The initial product is the 2-imidazoline, which needs to be aromatized by treatment with active manganese dioxide [10]. 

To a solution of the imidazoline (7.5 g) in chloroform (150 ml) is added active manganese dioxide (30 g). The suspension is stirred at room temperature (16 h) then filtered, and the solid washed with hot chloroform. Evaporation of the combined chloroform fractions gives the imidazole ester (5.2 g). Sublimation at 80°C (0.05 mmHg) gives the pure product, m.p. 97-98°C. 

The isomeric 1-suhstituted imidazole-5-carboxylates are made by cyclization of 3-amino-2-alkylaminopropanoic acids with triethyl orthoformate followed by active manganese dioxide oxidation of the imidazoline product (see Section 3.1.1), or from IV-substituted glycine esters, which are formylated, converted into the enolates and then condensed with potassium thiocyanate... 

Imidazole-2-carbaldehyde is obtained in 70% yield from imidazole-2-methanol and the six-fold amount of activated manganese dioxide-B in anhydrous ether, acetone, or CC14 at 20°.422... 

Reaction of lithium aluminum hydride followed by manganese dioxide converts 5-oxyl-l,2,5,6,7,7a-hexahydroimidazo[l,5-A][l,2,4]oxadiazol-2-one (109) into the l-oxyl-2,5-dihydro-l//-imidazole (110) (Equation (16)) <93T10693>. 

---