Oxidations of 4H‐1,2,6‐Thiadiazines

Abstract

AbstractThe oxidation of various non‐S‐oxidized 4H‐1,2,6‐thiadiazines with N2O4, meta‐chloroperbenzoic acid (m‐CPBA), Oxone, [bis(trifluoroacetoxy)iodo]benzene (PIFA) and phenyliodine (III) diacetate (PIDA) is reported. Six 3,5‐diamino‐4H‐1,2,6‐thiadiazin‐4‐ones were oxidized to the corresponding sulfones (67–95 % yields) most efficiently using PIFA (3 equiv.). A 3,5‐diphenylthio analogue, however, oxidized at the exocyclic sulfur to give the asymmetric mono sulfoxide using PIFA (3 equiv.) in 86 % yield. 4H‐1,2,6‐Thiadiazine 4‐ylidenemalononitriles, 4‐ylidinemalonates and 4‐phenylimines were oxidized stepwise, initially to sulfoxides using all the above reagents in 31–97 % yields and then to sulfones using N2O4, m‐CPBA or Oxone in 31–89 % yields. Oxidation of a 4‐thione derivative using Oxone (1.5 equiv.) gave the sulfine in 56 %. Unexpectedly, oxidation of 3,5‐diphenyl‐4‐(phenylimino)‐4H‐1,2,6‐thiadiazine 1‐oxide with excess m‐CPBA gave a fused oxaziridine in 98 % yield, while 3,5‐dimorpholino‐4H‐1,2,6‐thiadiazin‐4‐one 1,1‐dioxide in EtOH/MeCN gave a hemiacetal in 56 % yield. Single crystal structures of 3,5‐bis(phenylamino)‐4H‐1,2,6‐thiadiazin‐4‐one 1,1‐dioxide, 4‐ethoxy‐4‐hydroxy‐3,5‐dimorpholino‐4H‐1,2,6‐thiadiazine 1,1‐dioxide, 2‐(1‐oxido‐3,5‐diphenyl‐4H‐1,2,6‐thiadiazin‐4‐ylidene)malononitrile, 2‐[1,1‐dioxido‐3,5‐di(thien‐2‐yl)‐4H‐1,2,6‐thiadiazin‐4‐ylidene]malononitrile and (E)‐4,6‐diphenyl‐5‐(phenylimino)‐7‐oxa‐2‐thia‐1,3‐diazabicyclo[4.1.0]‐hept‐3‐ene 2,2‐dioxide are reported.