First [4+2] cycloaddition of alkynyl Fischer carbene complexes with heterodienes. Facile synthesis of 1,4-dihydropyridines from 1-azadienes

✍ Scribed by José Barluenga; Miguel Tomás; JoséA. López-Pelegrín; Eduardo Rubio

• Book ID: 104257099
• Publisher: Elsevier Science
• Year: 1997
• Tongue: French
• Weight: 172 KB
• Volume: 38
• Category: Article
• ISSN: 0040-4039
• DOI: 10.1016/s0040-4039(97)00737-5

✦ Synopsis

Neutral 1-azadienes react in a [4 + 2] fashion with alkynyl Fischer carbene complexes to afford regioselectively substituted 1.4-dihydropyridines © 1997 Elsevier Science Ltd.

We have recently reported the reaction of 1-azadienes with chromium Fischer alkynyl carbene complexes that results in the formation of azepines through a clean [4 + 3] annulation. 1 In the course of that study we discovered that, in some cases, a small amount of the [4 + 2] cycloadduct was also obtained. We focussed on this observation since the reluctance of 1-azadienes to undergo [4 + 2] cycloadditions is very well documented. Although one example of cycloaddition of unactivated 1-azadiene with enamines has been reported, 2 their reaction with electron poor dienophiles is not expected and indeed, it remains unknown. 3 On the other hand, a range of [4 + 2] cycloadditions of activated carbodienes with alkynyl Fischer carbene