Cobalt-catalyzed cross-coupling of Umpolung carbonyls with alkyl halides under mild conditions
作者:Ruofei Cheng、Graham de Ruiter、Chao-Jun Li
DOI:10.1039/d2cc04302e
日期:——
dominated by palladium and nickel catalysts, cobalt-based catalysts have shown unique advantages for such cross-coupling reactions in terms of higher catalyticactivity and lower toxicity. Herein, we describe a novel cobalt-catalyzed alkyl–alkyl cross-coupling reaction of hydrazone with alkylhalides under mild reaction conditions, where the use of a PNP-type pincerligand is essential for catalysis
Various CH(2)X groups have been attached to the ortho position of phenylcarbene. If 2'- or 3'-C-H bonds are present, as in 23 (X = Me), 71 (X = CMe(3)), and 58 (X = SiMe(3)), C-H insertion leading to five- or six-membered rings predominates in the gas phase and competes with intermolecular reactions in solution. The formation of benzocyclobutenes via insertion into 1'-C-H bonds is a very minor reaction path of 23 and 71. In contrast, 58 produces substantial amounts of the benzocyclobutene 59 by way of C-Si insertion, particularly in the gas phase. Insertion into the Si-Me bonds of 58 also occurs while the C-F bonds of 37 (X = CF3) and 50 (X = Fl are inert. In the gas phase, 37 and 50 give mainly benzocyclobutenes whereas intermolecular reactions prevail in solution. The effects of sensitization and of solvent polarity suggest that benzocyclobutenes arise from singlet arylcarbenes. The amount of carbene-carbene rearrangement decreases in the order 7 (X = H) > 37 (X = CF3) > 23 (X = Me); no rearrangement was observed with 50 (X = Fl, 58 (X = SiMe(3)), and 71 (X = CMe(3)).
New precursors for arylcarbenes. Photocycloelimination reactions of cyclic sulfites