Arsoles, cycloaddition

B-90MI 316-03) have been surveyed. Syntheses of 1,3-diphospholide anions were mentioned in a review on the chemistry of l,2-dihydro-l,2-diphosphetes <92Ml 316-01). The reactivity of 1,3-heterophospholes is discussed in some of the cited reviews. A review on cycloaddition reactions to P=C and As=C double bonds <86PS(26)203) mentions 1,3-benzoxaphospholes and 1,3-benzox-arsoles as examples. Besides that, only one 1978 and one 1994 review deal with 1,3-heteroarsoles [Pg.718]

The family of 1,3-benzoxaphospholes (9) and -arsoles (25) includes the 2-alkyl-1,3-benzoxaphos-pholes/arsoles, which are colorless liquids, thermally stable up to 130°C. The 2-aryl derivatives are yellow crystalline solids <80JOM(l 86)39,802tC342,83ZC439, 85PS(25)345>. Air oxidation of the alcoholic solution is fast for the 2-methyl, medium for the 2-/-butyl, and slow for the 2-phenyl derivatives. It probably proceeds via cycloaddition of the triplet oxygen to the P/As=C bond, and its subsequent fission. 

Protonation of the arsole anion (68) yields predominately the endo-bicyclic system (71). This reaction finds analogy in phosphorus chemistry and is believed to occur by initial formation of the 177-arsole (69), which tautomerizes to the 2i7-arsole (70) and then undergoes cycloaddition to give primarily the e do-product (Scheme 10). Some of the exo-isomer is observed by H NMR. The endo-dimer is converted into the exo-dimer by heating at 95°C for 16 h <91CB2453>. 

Arsoles exhibit rich cycloaddition chemistry. They react at room temperature with strongly electron-withdrawing alkenes to give stable Diels-Alder adducts (75), which transfer their arsenic moiety to dimethylbutadiene at elevated temperature to give diene derivatives. In some cases, the... 

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