Copper‐Mediated One‐Pot Access to Benzo[b][1,4]thiazines from 2‐N‐Sulfonylaminoaryl Disulfides

Abstract

Abstract2‐N‐Sulfonylaminoaryl disulfides can be converted into the corresponding benzo[b][1,4]thiazines in one pot when reacted with an electron‐rich alkene in the presence of a base and a substoichiometric amount of a copper salt. Depending upon the reaction conditions, and in particular the copper salt used, we observed the concurrent formation of variable amounts of the corresponding benzo[b][1,4]thiazine S‐oxides that are not the result of a post‐oxidation reaction. The overall procedure can provide simple access to benzo[b]thiazines or thiazine S,S‐dioxides by sequential reduction or oxidation of the crude reaction mixtures.

Copper‐Mediated One‐Pot Access to 2,3‐Dihydrobenzo[b][1,4]oxathiines from o,o′‐Dihydroxydisulfides

“…We started studying this reaction using disulfide 8a as a possible precursor of the parent o ‐thioquinone 7a (Scheme , R=H), p ‐methoxystyrene ( 10a ) (2 equiv) was chosen as a suitable trapping electron‐rich dienophile, and Et 3 N (1 equiv) as a base. Working in chloroform at 60°C, we initially verified that the reaction did not occur without a catalyst and then tested the ability of different copper LAs such as Cu(OAc) 2 , CuI, CuO, and Cu(acac) 2 to promote the reaction. As for the corresponding iminothiones and selenones, Cu(OTf) 2 (20% mol) was the only LA that allowed the isolation of expected benzoxathiine 2e , which, after 68 h at 60°C in chloroform and column chromatography, was obtained in a quite low yield (11%) as shown in Scheme .…”

“…A detailed analysis of the crude mixture, isolated after 68 h at 60°C, did not show any other derivative having the benzoxathiine skeleton. In particular, we did not observe the formation of oxathiine‐ S ‐oxide derivatives as it happens for the corresponding o,o ′‐di‐ N ‐tosylaminodisufide that, reacted under the same condition, led to isolation of dihydrobenzo[ b ][1,4]thiazines that were always accompanied by a variable amount of the corresponding dihydrobenzo[ b ][1,4]thiazine‐ S ‐oxides .…”

“…We have recently reported that transient dienic o ‐iminothioquinones (and o ‐iminoselenoquinones ) can be obtained from the corresponding o , o ′‐di‐ N ‐tosylaminodisulfides (or o , o ′‐di‐ N ‐tosylaminodiselenides) through a copper‐mediated 1,4‐elimination at sulfur (or selenium). The latter species can be trapped in an IEDDAR to give, under mild reaction conditions, 2,3‐dihydrobenzo[ b ][1,4]thiazines (and 2,3‐dihydrobenzo[ b ][1,4]selenazines ). The scope and extension of this new method to the preparation of o ‐thioquinones 7 is described in this paper.…”

“…We envisaged that a procedure related to those used for iminothioquinones and iminoselenoquinones could be applied to o,o ′‐dihydroxydisulfides. In particular, as depicted in Scheme , we hypothesized to react an o,o ′‐dihydroxydisulfide 8 with a proper Lewis acid (LA) in the presence of a Brønsted base such as Et 3 N. Thus, phenolic OH deprotonation and disulfide sulfur interaction with LA could trigger a 1,4‐elimination at sulfur of the thiolate ion 9 and formation of thioquinone 7 .…”

“…In fact, the ability of reacting as electron‐poor dienes with 1,3‐dienes working as dienophiles is typical of o ‐thioquinones and related hetero‐quinoid systems . As in the case of o ‐iminothiones and o ‐iminoselenones produced using this copper‐mediated procedure, no cycloadduct was obtained using phenyl vinyl sulfide 10f as a dienophile. A possible interaction of 10f with the catalyst, thus eliminating those with the disulfide and the consequential 1,4‐elimination at sulfur, cannot be ruled out; however, we demonstrated that reacting 8d in the presence of both 10f and 10a the oxathiine 2h was still isolated albeit in lower yields (51%).…”