Stereospecific multi-step elimination of methanol involving 1,4-methoxyl migration from the MH+ ion of 2,3-cis-3-methoxytricyclo[6.2.2.02,7]dodeca-9-ene

✍ Scribed by Morlender-Vais, N.; Mandelbaum, A.

• Publisher: John Wiley and Sons
• Year: 1999
• Tongue: English
• Weight: 447 KB
• Volume: 34
• Category: Article
• ISSN: 1076-5174
• DOI: 10.1002/(sici)1096-9888(199904)34:4<291::aid-jms751>3.0.co;2-i

✦ Synopsis

The elimination of methanol from the MD' ion of 2,3-cis-3-methoxytricyclo [ 6.2.2.02,7 ] dodeca-9-ene, endo-2, upon chemical ionization (CI) gives rise to both [ MD Ô MeOD ] ' and [ MD Ô MeOH ] ' ions. Only the [ MD Ô MeOH ] ' ion is formed under collision-induced dissociation (CID) conditions. This is in contrast with the behavior of the 2,3-trans-stereoisomer exo-2 and with saturated analogs which undergo exclusive elimination of MeOD. The unusual elimination of MeOH from endo-2 indicates transfer of the external deuteron in the MD' ion from the oxygen atom to the interior of the organic moiety and a back transfer of a hydrogen from the organic moiety to the oxygen atom prior to the CwO bond dissociation step. A deuterium labeling study showed that the hydrogen atom involved in this elimination process originates at position 3 (formal 1,1-elimination). These results suggest a multi-step mechanism for this unique stereospeciÐc methanol elimination, initiated by a proton transfer from the methoxy group to the double bond followed by a 1,4-methoxyl migration from C-3 to C-10. The proposed mechanism Ðnds support in the CI and CID study of deuterium-labeled analogs which have a methoxy group at position 10.