A Versatile Aminobenzannulation Method Based on the Deprotonation of 2-(1-Alkynyl)benzaldimines and Similar 2-Aza-2,4-heptadienyl-6-ynes: A Multistep Rearrangement Cascade

✍ Scribed by Pramod Sagar; Roland Fröhlich; Ernst-Ulrich Würthwein

• Publisher: John Wiley and Sons
• Year: 2004
• Tongue: English
• Weight: 204 KB
• Volume: 43
• Category: Article
• ISSN: 0044-8249
• DOI: 10.1002/anie.200461031

✦ Synopsis

Benzannulation is a frequently used method to construct molecules and to modify their chemical and pharmaceutical properties. Modern transition-metal carbene complexes, [1] metal-catalyzed [2] and metal-free methods [3] have been used successfully for benzannulation reactions. In the course of the search for new synthetic routes for seven-membered heterocycles we have uncovered a new and versatile method for the synthesis of aminobenzannulated aryl, heteroaryl, and cycloalkyl compounds.

Whereas the deprotonation of 2-alkenylbenzaldimines and subsequent treatment with electrophiles lead to the expected [4] dihydrobenzazepines [5] by means of a highly diastereoselective anionic 8p electrocyclization (Scheme 1), the analogous alkynyl compounds behave completely differently upon deprotonation. Much to our surprise when we deprotonated alkynylimines 1 a,b by use of lithium diisopropylamide (LDA) at À78 8C, then warmed the reaction mixture to room temperature, and added the appropriate electrophile EX, we isolated the 1-aminonaphthalene derivatives 3 a-l generally in good to very good yield (Table 1; see Figure 1 for Scheme 1. 4,5-3H-Dihydrobenzo[c]azepines prepared by electrocyclization of 2-aza-4,5-benzoheptatrienyllithium compounds.