Asymmetric synthesis of 7-membered-ring-bridged 3,4-fused tricyclic indoles via Friedel-Crafts alkylation/annulation

With N-methyl-4-aminoindole as the 1,4-bisnucleophile, the regio- and enantioselective Friedel-Crafts alkylation/N-hemiacetalization and dehydration sequence with beta,gamma-unsaturated alpha-ketoesters was reported using 5 mol% Ni(ii)-PyBPI complex, affording diverse chiral 7-membered-ring-bridged 3,4-fused tricyclic indoles in good results (up to 91% yield and 97% ee). The by-products were 6-membered-ring-bridged 4,5-fused tricyclic indoles.