If there is a topic of catalysis that has been restlessly growing these past ten years, it is without much doubt the field of C-H activation. In it, C-H activation on Csp3 positions proves difficult, though more and more methods are developed. In particular, the C-H bonds borne by cyclopropane moieties seem to be activated reasonably easily by palladium complexes.
In 2012, the group of Prof. Nicolai Cramer of EPFL (Lausanne, Switzerland) reported a new enantioselective method for the synthesis of cyclopropane-fused tetrahydroquinolines via palladium-catalysed cyclopropane Csp3-H activation.
The only downside of the method is the mandatory substitution on the R position. In the case where R = H, the favoured product is the corresponding spiro dihydroindole compound.
This is easily understandable as the 6-membered ring product must come from a 7-membered ring intermediate whereas the 6-membered intermediate would be favoured, affording the 5-membered product.
Angew. Chem. Int. Ed. 2012, 51, 12842-12845. link