Conversion of imino-1,2,3-dithiazoles into 2-cyanobenzothiazoles, cyanoimidoyl chlorides and diatomic sulfur

Ring transformations of 2-hydroxy-(4-chloro-5 H -1,2,3-dithiazol-5-ylideneamino)arenes

“…Thermolysis and base mediated ring transformations. The relative thermal stability of the 2-hydroxy(dithiazolylideneamino) arenes 5aec was indicated during their isolation and purification: both the (dithiazolylideneamino)phenol and pyridin-3-ol 5a and 5c, respectively, can be recrystallised as yellow cotton fibres from warm c-hexane, however, the (dithiazolylideneamino)pyridin-2-ol 5b was unstable and partly cyclised into oxazolo [5,4-b]pyridine-2-carbonitrile (4b) affording also traces of [1,2,3]dithiazolo [5,4-e] pyrido [2,3-b] [1,4]oxazine (6b). Purification of the (dithiazolylideneamino)pyridin-2-ol 5b was, therefore, carried out via precipitation in n-pentane from THF.…”

“…27 Direct displacement of the dithiazoles C4 chlorine atom has proved to be difficult, 17a and the intramolecular cyclisation of the (dithiazolylideneamino)phenol 5a to afford the benzoxazine 6a is a very rare example of a cyclisation onto the dithiazole C4 position that maintains the integrity of the dithiazole ring. The only other known example is the reaction of 5-(4-chloro-5H-1,2,3-dithiazol-5-ylidene)-2,2-dimethyl-1,3-dioxane-4,6-dione (10) with secondary alkylamines to yield 6-carbamoyl-5-oxo-5H-furo [2,3-d] [1,2,3] dithiazoles (11) (Scheme 4). 28 However, this cyclisation proceeds via an ANRORC style mechanism where the amine attacks the ring sulfur to generate a disulfide intermediate that then recyclises.…”

“…Where the ortho substituent is a primary, secondary 19,24 or even a tertiary amine, 25 thermolysis affords the analogous imidazole-2-carbonitriles 3, and when the ortho substituent is a hydroxyl group the analogous benzo[d]oxazole-2-carbonitrile (4a) forms (Scheme 2). 17a,20 Surprisingly, in the latter case, treatment of 2-(4-chloro-5H-1,2,3-dithiazol-5-ylideneamino) phenol (5a) with NaH in dry THF gave benzo[b] [1,2,3]dithiazolo [5,4-e] [1,4]oxazine (6a) (Scheme 2). 17a Scheme 1.…”

“…21 Moreover, 1,2,3-dithiazolylideneamines have also been used to prepare acyclic functionalities such as isothiocyanates 22 and thiocyanoformamides. 2,23 Several examples of (4-chloro-5H-1,2,3-dithiazol-5-ylidene amino)arene ring transformations involve a nucleophilic ortho substituent on the arene. Where the ortho substituent is a primary, secondary 19,24 or even a tertiary amine, 25 thermolysis affords the analogous imidazole-2-carbonitriles 3, and when the ortho substituent is a hydroxyl group the analogous benzo[d]oxazole-2-carbonitrile (4a) forms (Scheme 2).…”

A tribute to Professor Oleg Alekseevich Rakitin

“…The period led to exciting discoveries of new heterocycles and ring transformations. The work focused on three strategies: i) an investigation of 4,5-dichloro-1,2,3-dithiazolium chloride 2 (Appel salt); [17][18][19] ii) a study of During sulfurization studies of 1,4-benzoquinones monooximes 8, Oleg and coworkers serendipitously discovered the mindboggling synthesis of an array of complex sulfur rich heterocycles. Treatment of comparatively simple starting materials such as trialkylamines [25][26][27] or dialkylsulfides 28 with the powerful DABCO/S 2 Cl 2 protocol gave fused 1,2-ditholes, 1,4-thiazines and polysufur systems such as 1,2,3,4,5-pentathiepin and heptathiocanes (Scheme 5).…”