N-Allylic Alkylation of Indoles

Significance: Modified cinchona alkaloid hydroquinidine 1,4-phthalazinediyl diether [(DHQD)2PHAL] (1) catalyzes the chemoselective asymmetric N-allylic alkylation of indoles with Morita–Baylis–Hillman carbonates. Moderate to excellent yields and enantioselectivities have been achieved and variation in the substitution pattern of electron-rich or electron-deficient indoles was well tolerated. Furthermore, it is shown that the N-allylic indole products can be converted into pyrrolo[1,2-a]indole and pyrrolo[3,2,1-ij]quinoline derivatives. Comment: Due to the C3-chemoselectivity of indole the majority of enantioselective reactions of indoles focus on this position, whereas asymmetric substitutions at nitrogen are rare and underdeveloped (see Reviews below). Moreover, by using Morita–Baylis–Hillman carbonates as substrates an asymmetric allylic alkylation is realized. This is an attractive method for accessing enantioenriched compounds that can easily undergo further transformations.