Diels-Alder reaction 2£,4£ -Dienamides

An intramolecular Diels-Alder reaction of allenic dienamide 181 provided the tet-rahydroindole ring system 182, which was oxidized with DDQ or Mn02 to give indole derivatives [147]. 

Another approach to the lycorane skeleton involving an intramolecular Diels-Alder reaction commenced with the conversion of the unsaturated nitrile 138 to the imine 139 by sequential reduction with diisobutylaluminum hydride followed by condensation with but-3-enylamine (Scheme 13) (118). When 139 was acy-lated with chloroethyl chloroformate in the presence of Hiinig base and the resulting dienamide heated at 140°C, the bicyclic carbamate 141 was isolated. If it is assumed that the Diels-Alder reaction proceeded via an exo transition state,... 

Diels-Alder reaction of the allenic dienamides (111). The corresponding cis-indolidines and indoles are readily prepared from the products (112) by standard reductive and oxidative methods, respectively. The fused five-, six-, and seven-membered nitrogen heterocycles (114) can be prepared in excellent yields from the... 

Biolatto B, Kneeteman M et al (1999) Diels-Alder reactions of lV-tosyl-3-nitroindole and dienamides synthesis of intermediates of Aspidospermine alkaloids. Tetrahedron Lett... 

Path B works back through cyclohexene 111 and an intramolecular Diels-Alder reaction of dienamine 112. Once again, enamine tautomerization is likely to present big problems, but once again this can be overcome by using dienamide 113. This plan provides an opportunity to control absolute stereochemistry if 113 could be prepared in enantiopure form. The dienophile olefin geometry would afford the proper relative stereochemistry at C2 and C3, but stereochemistry relative to 5 and Cio is not guaranteed. 

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