A deacetonative Sonogashira coupling of aryl chlorides and propargyl alcohols

While sp-sp2 couplings are now classics, whether using terminal alkynes, zinc, magnesium, boron or silicon alkynides, it is the first time I see a propargyl alcohol used as a partner in this type of coupling. The group of Yang and Wu (Zhengzhou University, China) reported last year a deacetonative “Sonogashira” coupling between aryl chlorides and tertiary propargyl alcohols:

13aIf you know your Name Reactions really well, it should remind you of the retro-Favorskii reaction, named after the Favorskii reaction (or Favorskii-Babayan reaction, see Scheme below), not to be confused with the Favorskii rearrangement.

13bReference: J. Org. Chem. 2013 10506-10511 link

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7. On cyclopropane C-H activation.

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.

7.b

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.

7.a

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.

7.c

Reference:
Angew. Chem. Int. Ed. 2012, 51, 12842-12845. link