Umsetzung von 3-Amino-2H-azirinen mit Salicylohydrazid

Abstract

Reaction of 3-Amino-2H-azirines with Salicylohydrazide. 3-Amino-2H-azirines 1a-g react with salicylohydrazide (7) in MeCN at 80° to give 2H,5H-1,2,4-triazines 10, 1,3,4-oxadiazoles 12 and, in the case of 1d, 1,2,4-triazin-6-one 11a (Scheme 3). The precursor of these heterocycles, the amidrazone of type 9, except for 9c and 9g, which could not be isolated, has been found as the main product after reaction of 1 and 7 in MeCN at room temperature. 3-(N-Methyl-N-phenylamino)-2-phenyl-2H-azirine (1g) reacts with 7 to give mainly the aromatic triazines 15b1 and 15b2. In this case, two unexpected by-products, 16 and salicylamide (17), occurred, probably by disproportionation of a 1:1 adduct from 1g and 7 (Scheme 8). Oxidation of 10f with DDQ leads to the triazine 15a. The structure of 10c, 11a , 12c, 13 (by-product in the reaction of 1b and 7), the N'-phenylureido derivative 14 of 9d (Scheme 4) as well as 15b, has been established by X-ray crystallography. The ratio of 10/12 as a function of substitution pattern in 1 and solvent has been investigated (Tables 1, 3, 4, and 7). A mechanism for the formation of 10 and 12 is proposed in Scheme 7.