Rather u(Ni)que: Two new C-H alkenylation reactions, that is C-H/C-O alkenylation and decarbonylative C-H alkenylation, of azoles are uniquely catalyzed by Ni/dcype. These azole alkenylation reactions are successfully applied to the convergent formal synthesis of siphonazole B.

C-H Alkenylation of Azoles with Enols and Esters by NickelCatalysis. -The utility of this new title reaction is demonstrated by the synthesis of compound (XVI) which is an intermediate in the synthesis of siphonazole B (XVII). -(MENG, L.; KAMADA, Y.; MUTO, K.; YAMAGUCHI*, J.; ITAMI, K.; Angew. Chem., Int. Ed. 52 (2013) 38, 10048-10051, http://dx.

Transition metal catalyzed alkenylation is one of the most reliable methods for making alkenyl-substituted arenes as exemplified by the Mizoroki-Heck reaction. [1] Recently, direct CÀH alkenylation [2] has received growing interest as an emerging tool for constructing alkenylated arenes and particularly alkenylated heteroarenes, since they are predominant motifs in biologically active natural products, pharmaceuticals and organic materials (Scheme 1 a). [3] Representative reaction types of CÀH alkenylation include (Scheme 1 b): 1) CÀH/CÀX alkenylation (X = halogens including triflates) of heteroarenes with alkenyl halides by using palladium and copper catalysts, [4] 2) CÀH/CÀH alkenylation (oxidative Mizoroki-Heck reaction) of heteroarenes with simple alkenes by using palladium and rhodium catalysts, [5] and 3) C À H addition of heteroarenes to alkynes by transitionmetal catalysts. [6] There also exist other CÀH couplings which are outside the realm of the above-mentioned category. [7] Meanwhile, our group has developed a number of unique C À H arylation reactions of heteroarenes catalyzed by transition-metal complexes. [8][9][10] For example, we recently discovered the first nickel-catalyzed C À H/C À O coupling of heteroarenes and phenol derivatives [10a] as well as a decarbonylative CÀH coupling between heteroarenes and aryl esters. [10b] These catalytic processes are unique among other CÀH arylation methods not only because they allow incorporation of unconventional aryl electrophiles in C À H arylation (phenol derivatives and arenecarboxylates), but also because these reactions are uniquely promoted by an enabling supporting ligand, 1,2-bis(dicyclohexylphosphino)ethane (dcype), on a nickel(0) catalyst (other closely related ligands display extremely low or no promoting effect in these catalyses).Based on these auspicious discoveries, we questioned whether unprecedented C À H alkenylations of heteroarenes would become possible with a Ni/dcype catalyst by using enol derivatives [Scheme 1 b, 4)] and a,b-unsaturated esters [Scheme 1 b, 5)] as alkenylation agents. The CÀH/CÀO alkenylation of heteroarenes is rare, [11] and the decarbonylative CÀH alkenylation is thus far unknown. Herein, we report the CÀH Scheme 1. a) Useful alkenyl-substituted heteroarenes. b) A classification of the type of direct CÀH alkenylation of heteroarenes.