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Endocyclische S N ‐Reaktionen am gesättigten Kohlenstoff? Vorläufige Mitteilung
Author(s) -
Tenud L.,
Farooq S.,
Seibl J.,
Eschenmoser A.
Publication year - 1970
Publication title -
helvetica chimica acta
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.74
H-Index - 82
eISSN - 1522-2675
pISSN - 0018-019X
DOI - 10.1002/hlca.19700530816
Subject(s) - chemistry , intramolecular force , nucleophile , intermolecular force , ring (chemistry) , stereochemistry , transition state , nucleophilic substitution , computational chemistry , medicinal chemistry , molecule , organic chemistry , catalysis
Fig. 1 illustrates a definition of the terms endocyclic and exocyclic SN ‐reactions, referring to intramolecular nucleophilic substitution processes that occur by an SN 2 ‐analogous mechanism. Crossing experiments show that the methyl transfer I → II (see scheme 1) does not follow the formally appealing mechanism of the endocyclic SN ‐process III; the reaction proceeds intermolecularly under all conditions investigated. Kinetic measurements indicate that the methyl transfer XI → XII (see scheme 3) occurs in a similar fashion. This behaviour is believed to follow from the preference of tetrahedral carbon for backside attack by the nucleophile in SN 2 ‐reactions. The general experience, according to which intramolecular reaction paths over cyclic transition states with ring sizes of 5 or 6 are preferred to their intermolecular counterparts, is not to be extrapolated to SN 2 ‐reactions at tetrahedral carbon.