Cyclopropanation of 5-methylene galactopyranosides by dihalo-, ethoxycarbonyl-, and unsubstituted carbenes

Cyclopropanation reactions of 6-deoxyhex-5-enopyranosides by methylene-zinc-iodide complex, dichlorocarbene, and rhodium ethoxycarbonyl complex addition afford optimum yields of the corresponding spirocyclopropanes. Surprisingly, a stereospecific spirocyclopropane derivative with the two halogens on the Upper face of the 4-hydroxy substituent is obtained. To get more insight on the dichlorocarbene cyclopropa nation process a computational study, based on DFT quantomechanic calculation was conducted. (c) 2008 Elsevier Ltd. All rights reserved.