Samarium(II) Iodide-Induced Reductive Cyclization of Unactivated Olefinic Ketones. Sequential Radical Cyclization/Intermolecular Nucleophilic Addition and Substitution Reactions

Article abstract of DOI:10.1021/jo00037a033

Samarium(II) iodide in the presence of HMPA effectively promotes the intramolecular coupling of unactivated olefinic ketones by a reductive ketyl-olefin radical-cyclization process.The reaction is quite general for the formation of 5- and 6-membered carbocycles and even provides modest yields in less facile cyclization processes as evidenced by the generation of methylcyclooctanol via an 8-endo cyclization.Sequential radical cyclization-intermolecular nucleophilic addition/substitution processes set the SmI2 reaction apart from its radical-chain, photochemical, and electrochemical counterparts.In addition to delineating the synthetic potential of this reaction, the role played by HMPA in enhancing SmI2 reactivity has been further refined, and a model correlating the high diastereoselectivity and product distribution in SmI2-promoted reductive coupling processes with HMPA concentration has been established.