Indoles Diels-Alder addition, intramolecular

XIII). A thermal retro-Diels-Alder reaction of 39 liberating cyclopen-tadiene was used to afford a diene oxime ether which cyclized to give a tetracyclic indole as a 3 2 mixture of diastereomers. Three additional steps served to convert this adduct to ( )-lysergic acid (40). Of particular interest here is the fact that simple oximino compounds are not normally reactive dienophiles, and the intramolecularity of the conversion is apparently crucial to the success of this transformation. 

In addition to the above intermolecular reactions, the intramolecular Diels-Alder cycloadditions of furo[3,4-b]indoles have also been reported. Herndon and coworkers [131] used the coupling reaction of the Af-benzylindolynal derivative 396 with Fischer carbenes 397a-b to obtain the carbazoles 398a-b, presumably via the... 

Boronic acid 225 and alkenylindole 226 underwent a domino 1,4-addition/intramolecular Diels—Alder cycloaddition/protodeboronation sequence to furnish indole twistenedione 227 in 40% yield. The boronic acid moiety is critical to promote the regioselective 1,4-addition, which generates an appropriately reactive dienolate. The indole double bond of... 

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