Spirocyclic scaffolds are prevalent in numerous naturally occurring products and pharmaceuticals, which exhibit important biological and pharmacological activities. In this communication, a Sc(OTf)₃/Bis(oxazoline) complex catalyzed asymmetric Diels-Alder reaction of 2-arylidene-1,3-indanediones with 2-vinylindoles has been developed. The reaction provides a convenient and practical approach to biologically useful and synthetically important spiro-tetrahydrocarbazoles in good yields with high enantioselectivities (16 examples, up to 92% yield, 94% ee). A representative procedure for this asymmetric Diels-Alder reaction is described below: Sc(OTf)₃ (0.02 mmol) and chiral tridentate diphenyl-pybox ligand IV (0.02 mmol) were dissolved in toluene (1.5 mL) and stirred for 30 minutes at room temperature. 2-Arylidene-1,3-indanediones (0.20 mmol) was added to the above-mentioned solution and stirred at 5 ℃ for another 30 minutes. The solution of 2-vinylindoles (0.20 mmol) in toluene (0.5 mL) was then added to the reaction system and the mixture was stirred until the complete consumption of substrates (as monitored by TLC). The reaction mixture was purified directly by flash column chromatography on silica gel (petroleum ether/ethyl acetate=15:1～10:1) to give the corresponding products.

Key words: Diels-Alder reaction, asymmetric synthesis, Lewis acid catalysis, 1,3-indanedione, tetrahydrocarbazole