No abstract

Trimolecular adducts resulting from condensation between indolin‐2‐one (or indoline‐2‐thione), (aryl)aldehydes, and Meldrum’s acid are useful intermediates for the synthesis of either 1,2,3,4‐tetrahydro‐1‐thiacarbazoles or spiro[pyrrolidino‐3,3′‐oxindoles] related to the natural product horsfiline. These latter compounds were obtained in a three‐step procedure characterized by acyl azide formation, Curtius rearrangement, and subsequent thermal spiro cyclization. The relative stereochemistry of the spiro derivatives was determined by comparison of NOESY data and calculated conformational analyses. (© Wiley‐VCH Verlag GmbH, 69451 Weinheim, Germany, 2002)

Synthesis of Carbazoles by a Balanced Four ComponentCondensation. -Multicomponent reaction between substituted indoles (I), aromatic aldehydes (II), and Meldrum's acid (III) yields the functionalized tetrahydrocarbazoles (IV) and (V) as mixture of diastereomers as well as side products like di-indoles (VI) or indolyl-propionic acid derivatives (VII). Improvements with respect to yield, selectivity, and purity can be achieved by microwave assisted condensation, cf. (Ib). This type of condensation is not reserved to 2-carbon substituted indoles because indole-2-thione reacts smoothly with benzaldehyde and Meldrum's acid to the corresponding thiacarbazole. Since the multicomponent reaction appears to be reversible, this type of reaction could be a first step towards the development of a combinatorial version of the Yonemitsu reaction. -(COCHARD*, F.; LARONZE, M.; SIGAUT, P.; SAPI*, J.; LARONZE, J.-Y.;