Friedel-Crafts alkylation dihydroindoles

Less common 2-substituted indole derivatives can be prepared by Friedel-Crafts alkylation of 4,7-dihydroindoles with a,p-unsaturated aldehydes, followed by oxidation with p-benzoquinone [317]. 4,7-Dihydroindoles, which can be considered as 2,3-disubstituted pyrroles, react with a wide variety of aromatic and aliphatic enals... 

The ability of the less sterically hindered primary amines to perform iminium activation with challenging substrates such a,P-unsaturated ketones has been also applied to the Friedel-Crafts alkylation of 4,7-dihydroindoles using simple 1,2-vicinal diamines derived from L-leucine [329]. 

Primary-secondary diamine catalyst 14 was found to be useful in the Friedel-Crafts alkylation reaction (Scheme 3.20). In the presence of 14/trifluoroacetic acid (TFA), alkylation of 4,7-dihydroindoles 85 with a,(3-unsaturated enones 86 proceeded well, and the desired alkylation products were obtained in high yields and with excellent enantioselectivities [56]. 

---