Oxidations of 4<i>H</i>‐1,2,6‐Thiadiazines

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