3-Diethylamino-4- isothiazole 5,5-dioxide

Diethylamino-4-(4-methoxyphenyl)-isothiazole 5,5-dioxide 6 is (95T(51)2455) a highly reactive partner in 1,3-dipolar cycloadditions with several dipoles. Azomethine yhdes, such as oxazolones 7 and miinchnones 8, afforded with 6 bicychc pyrrolo[3,4-d]isothiazole 5,5-dioxides 9, 10, 11 in satisfactory yield. The regioselectivity of the reaction was excellent. The thermal behavior of these new bicychc systems was investigated. When heated at their melting point or shghtly above, triarylpyrroles 12, 13 were obtained through SOj and AtiV-diethylcyanamide ehmination. 

In the presence of various metal ions, 2-(fluoroenone)benzothiazoline has been found to rearrange to A-2-mercaptophenylenimine, while a free radical mechanism involving the homolysis of C-S and C-N bonds has been invoked to explain the formation of 3-phenyl-1,2,4-triazole derivatives from the thermal fragmentation and rearrangement of 2-(arylidenehydrazino)-4-(5//)-thiazolone derivatives. The cycloadducts (36) formed from the reaction of 3-diethylamino-4-(4-methoxyphenyl)-5-vinyl-isothiazole 1,1-dioxide (34) with nitric oxides or miinchnones (35) have been found to undergo pyrolytic transformation into a, jS-unsaturated nitriles (38) by way of pyrrole-isothiazoline 1,1-dioxide intermediates (37). 

Clerici et al. studied the reaction of 3-diethylamino-4-(4-methoxyphenyl)-5-vinyl-isothiazole 1,1-dioxides 15 with nitrile oxides and with munchnones. These reactions produced cycloadducts such as 16 and 17 which underwent thermal rearrangement to a, P-unsaturated nitriles <98T11285>. 

The reaction of sodium azide with 5-substituted 3-diethylamino-4-(4-methoxyphenyl)-isothiazole 1,1-dioxides afforded [l,2]thiazete 5,5-dioxides 56. It has been proposed that a nucleophilic addition of the azide ion to C-5 followed by ring closure gave a triazoline intermediate, which cyclized intramolecularly with concomitant nitrogen extrusion <02T5173>. 

Diethylamino-4-(4-methoxyphenyl)isothiazole-1,1-dioxide (17 Ar = 4-MeOPh) on treatment with one equivalent of bromine gave the dibromo derivative (18) which upon heating or by reaction with triethylamine furnished the mono bromo compound (19) on elimination of HBr. Palladium catalysed coupling of (19) with a variety of organostannanes provided good yields of 5-substituted isothiazoles (20) <97T15859>. 

Tin Reagents. Vinyltrialkyltin reagents can be used for introduction of alkenyl substituents into the 4-position in N-protected imidazoles 130 (Scheme 55). In this particular case alkenylation reaction under Heck conditions was unsatisfactory due to facile homocoupling of the heterocycle. A related series of reactions has been used for introduction of an allylic alcohol substituent into the imidazole 4-position in a ribosylimidazole nucleoside 131.Vinylation of 5-bromo-3-diethylamino-4-(4-methoxyphenyl)isothiazole 1,1-dioxide 132 with vinylstannane reagents can be used for the preparation of 5-alkenylated isothiazole 1,1-dioxides. "... 

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