Endocyclische SN‐Reaktionen am gesättigten Kohlenstoff? Vorläufige Mitteilung

Publisher Website
Google Scholar
Abstract
Fig. 1 illustrates a definition of the terms endocyclic and exocyclic SN‐reactions, referring to intramolecular nucleophilic substitution processes that occur by an SN2‐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 SN2‐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 SN2‐reactions at tetrahedral carbon.