Tetrahydropyran Ring-Opening Reactions Promoted by SmI_2

摘要

Many reductive transformations promoted by samarium diiodide (SmI_2) are used in ring-forming reactions; however, ring-opening reactions remain a far less studied area. Ketones and other carbonyl functions react readily with SmI_2 to form metal-associated ketyls possessing both free radical and anionic character. However, ring scission by the ejection of tethered atoms adjacent to carbonyl functions via SmI_2-generated ketyls is currently limited to small rings (1, n = 1) as shown in Scheme 1. Several noteworthy synthetic efforts have been achieved using epoxides, vinyl epoxides, and cyclo-propanes with the ring opening driven by strain energy release to afford general structure 2 (n = 1) rather than the direct reduction product 3 (n = 1).