1H-phosphindoles as structural units in the synthesis of chiral helicenes

Building helicenes: A photochemical cyclization approach affords helicenes in which the fused ring sequence ends with a phosphole unit (see scheme). The stereogenic phosphorus centers of the substrates control the screw sense of helical chirality. The terminal phosphole units undergo photochemical [2+2] annulations to give dimeric helical structures. Copyright © 2012 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.