One‐Pot Synthesis of Pyrrolo[1,2‐ a ]indoles by Chiral N ‐Triflyl Phosphoramide Catalyzed Friedel‐Crafts Alkylation of 4,7‐Dihydroindole with β , γ ‐Unsaturated α ‐Keto Esters

Chiral N ‐triflyl phosphoramide was found an efficient catalyst for the enantioselective Friedel‐Crafts alkylation reaction of 4,7‐dihydroindole with β , γ ‐unsaturated α ‐keto esters. In the presence of 5 mol% of the optimized catalyst, various pyrrolo[1,2‐ a ]indoles were obtained in excellent enantioselectivity, moderate yields and up to 3:1 diastereoselectivity based on the one‐pot synthesis including the Friedel‐Crafts alkylation reaction and the subsequent p ‐benzoquinone oxidation.