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Stereospecific multi‐step elimination of methanol involving 1,4‐methoxyl migration from the MH + ion of 2,3‐ cis ‐3‐methoxytricyclo[6.2.2.0 2,7 ]dodeca‐9‐ene
Author(s) -
MorlenderVais N.,
Mandelbaum A.
Publication year - 1999
Publication title -
journal of mass spectrometry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.475
H-Index - 121
eISSN - 1096-9888
pISSN - 1076-5174
DOI - 10.1002/(sici)1096-9888(199904)34:4<291::aid-jms751>3.0.co;2-i
Subject(s) - chemistry , moiety , stereospecificity , deuterium , dissociation (chemistry) , methanol , medicinal chemistry , stereochemistry , hydrogen atom , double bond , ion , elimination reaction , hydrogen bond , molecule , organic chemistry , group (periodic table) , catalysis , physics , quantum mechanics
The elimination of methanol from the MD + ion of2,3‐ cis ‐3‐methoxytricyclo[6.2.2.0 2,7 ]dodeca‐9‐ene, endo ‐2,upon chemical ionization (CI) gives rise to both[MD−MeOD] + and[MD−MeOH] + ions. Only the[MD−MeOH] + ion is formed undercollision‐induced dissociation (CID) conditions.This is in contrast with the behavior of the 2,3‐ trans ‐stereoisomer exo ‐2 and with saturatedanalogs which undergo exclusive elimination of MeOD. The unusualelimination of MeOH from endo ‐2 indicates transfer ofthe external deuteron in the MD + ion from the oxygenatom to the interior of the organic moiety and a back transfer of ahydrogen from the organic moiety to the oxygen atom prior to theCO bond dissociation step. A deuterium labeling study showedthat the hydrogen atom involved in this elimination processoriginates at position 3 (formal 1,1‐elimination).These results suggest a multi‐step mechanism for this uniquestereospecific methanol elimination, initiated by a proton transferfrom the methoxy group to the double bond followed by a1,4‐methoxyl migration from C‐3 to C‐10. Theproposed mechanism finds support in the CI and CID study ofdeuterium‐labeled analogs which have a methoxy group atposition 10. Copyright © 1999 John Wiley & Sons Ltd.