An Unexpected Isomerization of N‐Aryl‐3‐amino‐4‐nitroisothiazol‐5(2H)‐imines to 2‐(Benzothiazol‐2‐yl)‐2‐nitroethene‐l, l‐diamines

Abstract

The syntheses of several N-aryl-3-amino-4-nitroisothiazol-5(2H)-imines 12 from 3,3-diamino-2-nitrothioacrylamides 11 are reported (Scheme 3). In polar solvents, a spontaneous isomerization of some of the prepared isothiazol-5(2H)-imines 12 yielded benzothiazoles 13 (Scheme 4). In the case of 2-alkyl-substituted derivatives of type 12, the isomerization occurred only at higher temperatures. Electronic influences of different substituents on the rate of the isomerization were studied, and a polar reaction mechanism is proposed in Scheme 6. The structures of 12e and 13e were established by X-ray crystallography. Conformational analyses of 3-(methylamino)-2-nitro-N-phenyl-3-(pyrrolidin-l-yl)thioacry~amide (1 1 I) by NMR and X-ray methods were performed with the aim of explaining the distinct behavior of this amide towards Br, or diethyl azodicarboxylate.

Isothiazoles (1,2-thiazoles): synthesis, properties and applications

“…K 2 SO 4 ) involves selectively the exocylic sulfur atom and affords the corresponding 5-alkylsulfonylisothiazoles 162 in high yields. 123,124 The oxidation of the methylene group in substituted acetamide 163 by dimethylformamide dimethylacetal (164), which can be regarded as a variant of the condensation reaction associated with the elimination of two MeOH molecules, gives enamino ketone 165. 125 The chlorination of 5-[2-(N-tert-butyldimethylsilylamino)vinyl]isothiazoles 166 with N-chlorosuccinimide (NCS) proceeds selectively at the vinyl group resulting in the Z-isomers of isothiazole 167.…”

“…161 The reaction of 3-diethylamino-4-(4-methoxyphenyl)isothiazole 1,1-dioxide (199) with organomagnesium compounds in THF occurs via ring opening leading to a mixture of E-and Z-isomers of 3-substituted 2-arylpropeneamidines 247. 162 The chemistry of the 4-nitroisothiazole-5(2H)-imine derivatives 248, particularly, their isomerisation and desulfurisation, has been discussed in the papers 163,164 and a recent review. 165 It has already been noted (Section III.2) that the photolysis of 4-phenylisothiazole in benzene gives small amounts of 4-phenylthiazole (238) as a result of a rearrangement; cyanothiol 249, which was trapped as benzyl sulfide 250, is the main photolysis product in the absence of a base.…”

Imines, enamines and oximes

“…In polar solvents a spontaneous isomerisation to benzothiazoles 75 occurred, although some of the isothiazol-5(2H)-imines (Scheme 26) required heating. 130 A thermal rearrangement of the C,N-dialkynylimine 76, a proposed aza-Bergman rearrangement occurring via the intermediacy of 77, has been observed to give the olefin 78 in 88% yield with Z : E ratio of >95 : 5 (Scheme 27). 131 Isomerisation of ketimines to aldimines can be achieved if N-benzylimines are treated with ruthenium hydride complexes [RuH 2 (N 2 )(PPh 3 ) 3 or RuH 2 (PPh 3 ) 4 ] in toluene or dioxane under a hydrogen atmosphere.…”