Reactions of enamino-ketones. Part II. Synthesis of 4H-1,4-benzothiazines

Abstract

Die Kondensation von o‐Aminophenol (I) mit Cyclohexandionen (II) liefert die Phenothiazinonderivate (III).

Reaction between 2,2′-dithiodianiline and activated alkynes. Synthesis of 4H-1,4-benzothiazines

“…On the basis of these findings we can rationalise some results obtained from the reaction between the disulphide (1) and the alkyne (2c), namely: (a) benzothiazole (5) formation, (b) a possible way for benzothiazoline (4c) formation, and (c) the absence of the (2)-isomer of compound (6).…”

“…To gain insight into the formation of these latter products, we verified that under the above conditions the following reactions also occurred: (i) thermal decomposition l2 of benzothiazoline (4c) yielded only the expected benzothiazole (5) in 42% yield, (ii) cyclisation (6) -+ (4c) did not go to completion; the benzothiazoline (4c) and the benzothiazole (5) were obtained in 13% and 9% yield respectively together with 74% of recovered starting material. (iii) The known l1 p- (6) and its (2)-isomer [very probably arising from an ionic rather than radical addition of 2-aminobenzenethiol to alkyne (2c) *], cyclised at a different rate to compound (4c). It follows that, contrary to what was previously observed for the cyclisation of (6), its (2)-isomer under identical conditions yielded the benzothiazoline (4c) quantitatively in CQ.…”

A facile synthesis of 1,4-benzothiazines under solvent free conditions

“…The products of the condensation were found to be 2,3-disubstituted 1,4-benzothiazines and their melting points and spectral data are in good agreement with those reported in the literature. 22,23 The probable mechanism of the condensation is depicted in Scheme 1. Melting points as well as the observed yields of the products are presented in Table 1.…”

Ionic Liquids-Prompted Synthesis of Biologically Relevant Five- and Six-Membered Heterocyclic Skeletons

“…The optimum catalyst loading for [BMIM][Br] was found to be 20 mol%. The transformation when carried out in DMSO as a molecular solvent under 30-40 min of refluxing afforded products in comparatively low yield (62-72%) [281]. Use of catalyst in 25 mol% resulted in almost the same yield and diastereoselectivity.…”