A cyclic thioketone as biradical heterocyclopentane-1,3-diyl: synthesis, structure and activation chemistry

Abstract

The reaction of the biradical [(μ-NTer)P˙]₂ with thiophosgene, SCCl₂, leads to a cyclic phospha-aza thiourea derivative in very good yields. This synthetic approach represents a new possibility to prepare cyclic thioketones starting from four-membered cyclo-diphosphadiazanediyls by formal CS insertion with simultaneous oxidation of the two phosphorus atoms by the two chlorine atoms. When the phospha-aza thiourea derivative is reduced with magnesium chips, a deep blue, highly labile cyclic thioketone is formed, which can be regarded as a biradical heterocyclopentane-1,3-diyl. This new biradical can be converted to a housane species by light, which triggers transannular P–P bond formation. A thermal back-reaction was not observed, but scavenging reactions with CS₂ or PhCHO clearly indicate the intermediate formation of the labile, biradical cyclic thioketone. Various intercepted products, such as [2.2.1]bicyclic cage compounds could be isolated and structurally characterized. Freshly in situ generated biradical thioketone can be utilized to activate small molecules.