Preparation, reactions, and structure of 5,10-epoxy-, 5,10-epithio-, 5,10-episeleno-, and 5,10-epitelluro-5,10-dihydroarsanthren

Abstract

The compound recorded by Kalb (1921) as ‘arsanthren oxide’ has been more fully investigated. Its monomeric nature, now established, confirms that it is 5,10-epoxy-5,10-dihydroarsanthren. Its ready formation by hydrolysis of 5,10-dichloro-5,10-dihydroarsanthren with cold aqueous sodium carbonate presumably proceeds by the cyclisation of the intermediate 5-chloro-10-hydroxy- or 5,10-dihydroxy-compound. If the 5,10-dichloro- 5,10-dihydroarsanthren, like the 5,10-dimethyl analogue, has the folded ‘butterfly’ conformation, with the two substituents in the cis position, this process involves a flexing of the molecule about the As–As axis, which for steric reasons can be complete only when the two substituents react to form a five-membered ring.

The 5,10-epoxy-compound is unaffected by boiling methyl iodide, but is readily oxidised to arsanthrenic acid and is converted by methylmagnesium iodide into 5,10-dihydro-5,10-dimethylarsanthren. In ethanol it reacts rapidly with hydrogen sulphide, selenide, and telluride, giving the crystalline 5,10-epithio-, 5,10-episeleno-, and 5,10-epitelluro-analogues. X-Ray crystal analysis has established the complete structure and conformation of the 5,10-epithio-compound, but although this compound and the episeleno- and epitelluro-compounds have closely related cell constants, they are not isomorphous.

The u.v. i.r., n.m.r., and mass spectra of the four compounds are discussed. The mass spectral fragmentation patterns of various related arsanthren compounds are briefly recorded.