Palladium-Catalyzed Dearomative [4+2]-Cycloaddition toward Hydrocarbazoles

An efficient method for the construction of hydrocarbazoles bearing three continuous sterically hindered stereocenters, two quaternary and one tertiary, via a highly diastereoselective palladium-catalyzed [4 + 2]-cycloaddition/ dearomatization of 3-nitroindoles has been developed. The cycloaddition of 3-nitroindoles occurs at ambient conditions with a 1,4zwitterionic intermediate, in situ generated from gamma-methylidene-delta-valerolactones. The further synthetic utility of this method is demonstrated by the multifaceted transformations possible from the products. The catalytic asymmetric aspect of this transformation has also been explored.