Syntheses of New Multisubstituted 1-Acyloxyindole Compounds.

The syntheses of novel 1-acyloxyindole compounds and the investigations on reaction pathways are presented. Nitro ketoester substrate , obtained in a two-step synthetic process, underwent reduction, intramolecular addition, nucleophilic 1,5-addition, and acylation to afford 1-acyloxyindoles in one pot. Based on the systematic studies, we established the optimized reaction conditions for focusing on the final acylation step of the intermediate 1-hydroxyindole . With the optimized conditions, we succeeded in synthesizing 21 examples of new 1-acyloxyindole derivatives in modest yields (Y = 24 - 35%). Among the 1-acyloxyindole compounds, 1-acetoxyindole compounds were generally unstable, and their yields were relatively lower than the other 1-acyloxyindoles. We expect that a bulkier alkyl or aromatic group on R could stabilize the 1-acyloxyindole compounds. Significantly, one-pot reactions of a four-step sequence successfully generated compounds that are all new and might be difficult to be synthesized otherwise.