Stereospecificity and Concertedness of Retro-Diels-Alder Fragmentation in Some Diester Systems Upon Chemical Ionization

✍ Scribed by Denekamp, C.; Weisz, A.; Mandelbaum, A.

• Publisher: John Wiley and Sons
• Year: 1996
• Tongue: English
• Weight: 433 KB
• Volume: 31
• Category: Article
• ISSN: 1076-5174
• DOI: 10.1002/(sici)1096-9888(199609)31:9<1028::aid-jms388>3.0.co;2-k

✦ Synopsis

Retro-Diels-Alder (RDA) fragmentation of cis-and tuuns-2,3diethoxycarbonyl-5,6,7,8dihenzo bicyclo [ 2.2.2 J octanes under isobutane and methane chemical ionization conditions is highly stereospecific, giving rise to protonated diethyl maleate and fumarate, respectively. This behaviour indicates a single-step concerted mechanism, analogous to the ground-state RDA process that occurs in neutral molecules in the condensed phase. The analogous dissociation is partially stereospecific in stereoisomeric endo-, exo-and truns-2,3diethoxycarbonylbicyclo [ 2.2.1 1 heptanes and non-stereospecific in endo-, exo-and trans-2,3-diethoxycarbonyl-5,6benzobicyclo [ 2.2.23 octanes, indicating the involvement of a stepwise mechanism in the latter two systems. The different behaviour of the above systems is explained in terms of the energy of the RDA fragmentation. The differentiation and quantitative estimates of protonated diethyl maleate and fumarate were obtained from collisioninduced dissociation measurements.