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The Crystal and Molecular Structure of an Octacycloheneicosane Inert Towards Lewis Acid Isomerization
Author(s) -
Engel Peter,
Nowacki Werner,
Slutsky Joel,
Grubmüller Peter,
Schleyer Paul v. R.
Publication year - 1979
Publication title -
chemische berichte
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.667
H-Index - 136
eISSN - 1099-0682
pISSN - 0009-2940
DOI - 10.1002/cber.19791121106
Subject(s) - chemistry , isomerization , methylcyclohexane , lewis acids and bases , trimer , norbornadiene , frustrated lewis pair , crystal structure , hydride , dimer , crystallography , stereochemistry , computational chemistry , photochemistry , catalysis , medicinal chemistry , organic chemistry , hydrogen
Hydride transfer reduction (with 96% H 2 SO 4 and methylcyclohexane) of norbornadiene trimer ( 1 ) gives exo, exo ‐octacyclo[8.8.1.1 3,6 .1 12,15 .0 2,9 .0 4,8 .0 11,18 .0 13,17 ]heneicosane ( 4 ). The X ‐ray structural details of 4 and those calculated by force field methods are in excellent agreement. Further rearrangement of 4 to more stable C 21 H 28 isomers (e.g., 2 or 3 ) does not take place even with highly active Lewis acid catalysts. This exceptional behavior is attributed mechanistically to energetically unfavorable “bottlenecks”, i. e., intermediates with quaternary carbons and highly strained structures lying along the rearrangement pathway, which cannot be achieved under the reaction conditions without decomposition taking place.