AN ANOMALOUS SIMMONS-SMITH REACTION OF AN ALKENE TO FORM AN IODOMETHYL DERIVATIVE

An anomalous type of product from a Simmons-Smith reaction, involving the addition of the groups H and CH2I across the double bond, has been observed. When older samples of zinc-copper couple and diiodomethane are used in the reaction of 2-chloronorbornene (6), endo-2-chloro-exo-3-(iodomethyl)norbornane (7) is formed. Chloride 6 does proceed sluggishly via the classic reaction when fresh reagents are used, giving cyclopropanation to 4. Chloride 6 also is reluctant to add a methylene group via palladium(II) acetate catalysis when generated from diazomethane, giving poor yields of cyclopropyl chloride 4. Dehydrohalogenation of chloro iodide 7 was also studied, the main product being endo-2-chloro-exo-3-methylenenorbornane (8), though isomerization to 2-chloro-3-methylnorbornene (5) also occurs. Gas chromatography at higher temperatures with a certain packed column also isomerizes 8 to 5 and forms some exo-2-chloro-3-methylenenorbornane (9). © 1990, American Chemical Society. All rights reserved.