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Umlagerungen von Bicyclo[3.2.1]oct‐2‐en‐6‐yl‐ und Benzobicyclo[3.2.1]octenyl‐Kationen
Author(s) -
Kirmse Wolfgang,
Mönch Dietmar
Publication year - 1992
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.19921250540
Subject(s) - chemistry , bicyclic molecule , carbocation , degree of unsaturation , nucleophile , nucleophilic substitution , hydride , stereochemistry , propellane , medicinal chemistry , alkyl , organic chemistry , hydrogen , catalysis
Rearrangement of Bicyclo[3.2.1]oct‐2‐en‐6‐yl and Benzobicyclo[3.2.1]octenyl Cations The ketones 9, 27 , and 51 were prepared by modified or novel routes. The analogous tosylhydrazones 10, 28 , and 52 were photolyzed in 0.5 N NaOH (NaOD) to generate the carbocations 15, 34 , and 53 , respectively, by way of diazonium precursors. 2,3‐Unsaturation ( 15 ) and 2,3‐benzoanellation ( 34 ) affected the course of 4,6‐(4,5‐)hydride shifts, as elucidated by deuterium labeling. While the parent system 3 strongly prefers C‐5 over C‐6 (95:5) as the terminus of hydride shifts, 15 and 34 (55:45) approach the equivalence of C‐5 and C‐6 that is indicative of rapid Wagner‐Meerwein rearrangements or symmetrically bridged intermediates. This trend is attributed to flattening of the six‐membered ring in 15 and 24 , as compared to the chair conformation of 3 . On the other hand, predominant nucleophilic substitution at C‐6 is unaffected by 2,3‐unsaturation. We suggest that s̀ participation ( k Δ ) by alkyl groups is not sufficient to eliminate inverting displacement of nitrogen from the diazonium precursors by the solvent ( k s ). Equivalence of C‐5 and C‐6 toward external nucleophiles is achieved only by π participation, i.e. with the 3,4‐unsaturated and 3,4‐benzoanellated bicyclo[3.2.1]oct‐6‐yl systems ( 53 ).