Rearrangement reactions of aziridinylbenzaldoximes

Abstract

Reactions of 2,2‐dimethylaziridine with benzohydroximoyl chlorides [ArC(Cl)NOH] give aziridinylbenzaldoximes 1. It has been found that the aziridine ring in these compounds undergoes ring opening in hydrogen chloride‐dioxane solution to give (Z)‐N‐hydroxy‐N′‐(2‐chloro‐2‐methylpropyl)benzenecarboximidamides [ArC(NHCH2CR1R2Cl)NOH, 4]. Treatment of 1 with hydrochloric acid followed by neutralization with aqueous sodium hydroxide gave 6,6‐dimethyl‐3‐aryl‐1,2,4‐oxadiazines 2. Reaction of 4 with sodium hydride in dioxane gave 5‐isopropyl‐3‐aryl‐4,5‐dihydro‐1,2,4‐oxadiazoles 5. Reaction of the 4,5‐dihydro‐1,2,4‐oxadiazoles 5 with N‐chlorosuccinimide gave the heteroaromatic 1,2,4‐oxadiazoles 6. It is suggested that reactions of 4 with sodium hydride in dioxane solution involve the conjugate base of 4 which undergoes a 1,2‐hydride shift that is concerted with loss of chloride ion. In aqueous sodium hydroxide solution it is suggested that the conjugate base of 4 undergoes ionization of the chlorine atom followed by nucleophilic attack by the oximate anion.

Oxadiazoles

“…Oxidation of 4,5-dihydro-1,2,4-oxadiazoles 316 leads to fully conjugated 1,2,4-oxadiazoles 317; the oxidation has been performed with different oxidants such as N-chlorosuccinimide, manganese dioxide, and concentrated HNO 3 (Scheme 13.114) [125,162,169]. …”

Mass spectrometric analysis of 1,2,4‐Oxadiazoles and 4,5‐Dihydro‐1,2,4‐Oxadiazoles

“…There are other references where the synthesis of substituted 4,5-dihydro-1,2,4-oxadiazoles and their mass spectral data have been reported. These are: (Cavalleri, Bellani, & Lancini, 1973;Grundmenn, Bansal, & Osmanski, 1973;Hussein, 1987;Lessel, 1993Lessel, , 1995Chou et al, 1996;Johnson et al, 1996;Lessel & Herfs, 2000;Aitken et al, 2000).…”

“…SCHEME 19. Examination of the electron-impact behavior of 51a-c. Reproduced from the article of Johnson et al (1996), with permission from HeteroCorporation., Copyright 1996.…”

“…For example, Johnson et al (1996) provided the important ions and the relative intensities of compounds 3-isopropyl-3-phenyl-and 3-isopropyl-4-tolyl-1,2,4-oxadiazoles. Similarly, Nicolaides et al (1998) included the ions of some 3-(coumarin-4-yl)-1,2,4-oxadiazole derivatives.…”

“…Three 4,5-dihydro-1,2,4-oxadizoles were synthesized (Johnson et al, 1996) and the low resolution spectra of these SCHEME 12. (Continued) SCHEME 13.…”