1,7-ELECTROCYCLIZATION REACTIONS OF 2-AZAHEPTATRIENYL LITHIUM COMPOUNDS - SYNTHESIS OF 1-ACYL-2,3-DIHYDROAZEPINES

Deprotonation of the 2-aza-2,4,6-heptatriene 14 at -78 degrees C using lithium diisopropylamide as base yields the 2-azaheptatrienyl lithium compound 15. During warming up to 40 degrees C 15 undergoes a 1,7-ele ctrocyclisation to afford the 1-azacycloheptadienyl lithium compound 1 6, as predicted by quantum chemical ab initio calculations. This cycli sation reaction was monitored in detail by H-1 and C-13 NMR spectrosco py. Subsequent treatment with various acylating agents provides access to several 1-acyl-2,3-dihydroazepines 17. A X-ray diffraction structu re determination of derivative 17a shows a trans arrangement of the tw o aromatic substituents in 2- and 3-position, indicating a conrotatory mode of the ring closure reaction. The rotational barrier for the ami de rotation in 17b was determined to 15.4 kcal/mol. Copyright (C) 1996 Elsevier Science Ltd