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Synthesis 2006(13): 2183-2190  
DOI: 10.1055/s-2006-942414
PAPER
© Georg Thieme Verlag Stuttgart · New York

Electrocyclization Reactions of Benzannulated 2-Azaheptatrienyl- and 4-Azanonatetraenyllithium Compounds: Synthesis of N-Acylated 2,3-Dihydro-1H-benzo[c]azepines and a (5,6-Dihydrobenzocycloocten-5-yl)amine

Melanie Sajitz, Roland Fröhlich, Kirsi Salorinne, Ernst-Ulrich Würthwein*
Organisch-Chemisches Institut der Westfälischen Wilhelms-Universität Münster, Corrensstrasse 40, 48149 Münster, Germany
Fax: +49(251)8339772; e-Mail: wurthwe@uni-muenster.de;
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Publication History

Received 7 April 2005
Publication Date:
12 June 2006 (online)

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Abstract

Deprotonation of 2-alkenylbenzaldehyde N-benzyl­imines by lithium diisopropylamide and subsequent addition of pivaloyl chloride or methyl chloroformate yields 2-acylated 2,3-dihydro-1H-benzo[c]azepines. This reaction is interpreted as a cascade involving a 1,7-electrocyclization reaction and a subsequent 1,5-hydrogen shift. In contrast, 2-prop-1-enylbenzaldehyde N-allylimine leads to an N-acylated (5,6-dihydrobenzocycloocten-5-yl)amine upon deprotonation and addition of pivaloyl chloride. This transformation is interpreted as a reaction sequence consisting of a 1,7-electrocyclization, the addition of the electrophile, another deprotonation and a [2,3]-aza-Wittig rearrangement, which proceeds in two steps according to quantum chemical calculations.

Key words

ring closure - lithium - rearrangements - heterocycles - carbocycles - quantum chemical calculations

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