Thioxane ring

Thioxanes (60) give similar ring-opening reactions but the subsequent reaction to lose oxygen is not observed.1,3-Dithiolanes such as the cis and trans forms of (61) can be isomerized by Lewis acids but fail to undergo reduction with H2AICI this may be a consequence of solubility problems. 

Figure 9.6 Ring-flip dynamics of 1,4-thioxane and 1,4-dioxane inside 5...

Similar ring-closure procedures have been applied for the preparation of (12a, X = S) from 1,2-dichloro-1,2-dimethoxyethane [124] and (12c) from 2,3-dichlor-odioxane (see [68-70,81,124] and refs, cited therein). Also, the preparation of (20) from 2,3-dichloro-p-thioxane by a similar method has been reported veiy recently [265]. Scheme 3.4 outlines the preparation procedure of (12c) and (20) [68,265]. Compound (20) has also been prepared by a ring-closure procedure [111] starting from mercaptoethanol and methyl bromoacetate [235]. The derivative with X = O has limited shelf-life, even in the freezer, and it is used immediately after preparation [235]. 

Benzyne intermediates are probably involved in the ring-closure of 2-(or 3-) chloro-2 -(methylthio)benzophenones to thioxanthones. Xanthones were prepared analogously. Syntheses of several pharmacologically useful thioxan-thene derivatives have been described. Ceric ammonium nitrate oxidizes thioxanthene to thioxanthone. ... 

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