Clarification of the Reduction Behaver of Photoexcited Samarium Species and its Application to the Development of New Synthetic Process

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It has been revealed that the irradiation with visible light enhances the reducing ability of samarium diiodide. While the reduction of organic chlorides with SmIィイD22ィエD2 alone is difficult, irradiation with visible light causes the efficient reduction of organic chlorides to the corresponding hydrocarbons. Upon irradiation with visible light, gem-dichlorocyclopropanes undergo reductive dechlorination with samarium diiodide and benzenethiol to provide the corresponding cyclopropanes in good yields. The reaction may proceed via the hydrogen abstraction from PhSH by cycolopropyl radicals formed in situ by the reduction with SmIィイD22ィエD2. A novel photoinduced reduction of group 16 heteroatom compounds such as organic selenides, tosylates, and tellurides has also been developed. In particular, organic selenides, which can not be reduced with SmIィイD22ィエD2 in the dark (or even in the presence of HMPA), undergo reductive cleavage efficiently by using the SmIィイD22ィエD2-hv system. Moreover, the photoinitiated reaction of alkyl chlorides (R-Cl) with SmIィイD22ィエD2 in the presence of carbon monoxide (50 atm) is examined. The reaction provides the corresponding asymmetrical ketones (RC(=O)CHィイD22ィエD2R) as a carbonylated product. A mechanistic proposal includes the dimerization of acylsamarium species formed in situ by the reductive carbonylation of alkyl chlorides with CO and SmIィイD22ィエD2. Irradiation with near-UV light dramatically also enhances the reducing ability of ytterbium diiodide (YbIィイD22ィエD2). Organic bromides, iodies, tosylates, and tellurides are reduced efficiently by a YbIィイD22ィエD2-hv system, while these can not be reduced with YbIィイD22ィエD2 in the dark.