Premium
4,5‐Dihydro‐3 H ‐benzo[ c ]azepines from 1,7‐Electrocyclization Reactions of 2‐Aza‐4,5‐benzoheptatrienyllithium Compounds
Author(s) -
Gerdes Klaus,
Sagar Pramod,
Fröhlich Roland,
Wibbeling Birgit,
Würthwein ErnstUlrich
Publication year - 2004
Publication title -
european journal of organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 1434-193X
DOI - 10.1002/ejoc.200400206
Subject(s) - chemistry , pericyclic reaction , electrophile , ring (chemistry) , deprotonation , formylation , amide , dimer , cycloheptatriene , computational chemistry , benzylamine , conrotatory and disrotatory , medicinal chemistry , stereochemistry , organic chemistry , catalysis , ion
Various differently substituted (2‐alkenylbenzylidene)amines 4b − d gave, upon deprotonation with amide bases and addition of an electrophile, the respective 4,5‐dihydro‐3 H ‐benzo[ c ]azepines 6a − k in moderate to good yields. The imines 4 are easily accessible from 2‐bromobenzaldehyde ( 1 ) by Wittig olefination, formylation with DMF, and subsequent condensation with benzylamine. The ring‐closure reaction is interpreted as an anionic 1,7‐electrocyclization reaction involving benzo‐annulated 2‐azaheptatrienyllithium compounds. This reaction, and the subsequent addition of the electrophiles, proceed with excellent diastereoselectivity, determined by the ( E ) or ( Z ) configuration of the imines 4b − d . The corresponding allylimines 4e , f do not give ninemembered heterocycles 7 , but rather the corresponding 3‐vinyl‐4,5‐dihydro‐3 H ‐ benzo[ c ]azepines 6l , m . Molecular structures of several compounds 6 in the solid state were determined by X‐ray crystallography, including the structure of a 14‐membered ring dimer 8 . High‐level quantum chemical calculations on model anions concerning structures and relative energies of possible intermediates and transition states support the pericyclic mechanism suggested for the ring‐closure reaction. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)