Copper-catalysed cross-coupling of alkyl Grignard reagents and propargylic ammonium salts: stereospecific synthesis of allenes.

Herein we describe a robust and practical method to prepare enantiomerically enriched trisubstituted allenes using alkyl Grignard reagents and bench stable propargylic ammonium salts. Excellent yields as well as regio- and stereoselectivities are observed. Our conditions provide a solution to the allene racemization, which has been a long-standing problem when using Grignard reagents.

Ni Catalyzes the Regioselective Cross-Coupling of Alkylzinc Halides and Propargyl Bromides to Allenes.

We describe the unprecedented formation of allenes by Ni-catalyzed cross-coupling of propargyl bromides with alkylzinc halides. The reaction regioselectivity is complementary to the previously reported formation of propargyl-coupled compounds. Experiments support the formation of Ni complexes as the active species and the participation of radical intermediates.

Ni-catalyzed cascade cyclization-Kumada alkyl-alkyl cross-coupling.

Suggesting novel disconnections: A powerful Ni-catalyzed cascade reaction involving cyclization followed by cross-coupling allows the formation of up to three alkyl-alkyl bonds in a single operation by using alkene-containing alkyl iodides and Grignard reagents (see scheme; acac = acetylacetonate; TMEDA = N,N',N'-tetramethyl ethylenediamine). Mechanistic experimental and computational studies suggest a Ni(I)-Ni(II)-Ni(III) catalytic cycle and the intermediacy of radicals.