The radicalic cycloaddition of phenylarsine and trimethylsilylsubstituted phenylarsines to pentadiyn-1, 4-ones-3 yields the 2-methylene-arsolene-4-ones-3; these ketones react with diphenylketene to give the substituted 2, 3-bis-methylene-arsolenes-4, which undergo thermal electrocyclic reactions. The resulting benzannelated arsolenes are dehydrogenated to the corresponding arsoles, which can be isolated by reaction of phenylarsine with 3- ...