Copper‐Catalyzed Aerobic Oxidative Transformation of Ketone‐Derived N‐Tosyl Hydrazones: An Entry to Alkynes

Abstract

A novel strategy involving Cu-catalyzed oxidative transformation of ketone-derived hydrazone moiety to various synthetic valuable internal alkynes and diynes has been developed. This method features inexpensive metal catalyst, green oxidant, good functional group tolerance, high regioselectivity and readily available starting materials. Oxidative deprotonation reactions were carried out to form internal alkynes and symmetrical diynes. Cross-coupling reactions of hydrazones with halides and terminal alkynes were performed to afford functionalized alkynes and unsymmetrical conjugated diynes. A mechanism proceeding through a Cu-carbene intermediate is proposed for the CC triple bond formation.

In Situ Generation of Alkynylzinc and Its Subsequent Negishi Reaction in a Flow Reactor

“…4‐(Hex‐1‐yn‐1‐yl)benzonitrile (3cj): 1 H NMR (400 MHz, CDCl 3 ): δ = 7.48 (d, J = 8.4 Hz, 2H), 7.37 (d, J = 8.4 Hz, 2H), 2.35 (t, J = 6.8 Hz, 2H), 1.54–1.48 (m, 2H), 1.42–1.37(m, 2H), 0.87 (t, J = 7.6 Hz, 3H). 13 C NMR (100 MHz, CDCl 3 ): δ = 132.1, 131.9, 129.2, 118.7, 110.8, 95.7, 79.5, 30.5, 22.1, 19.2, 13.6.…”

Recent Development on Cp*Ir(III)‐Catalyzed C−H Bond Functionalization

“…Due to the readily occurring Glaser coupling as the side‐reaction in the directed C−H alkynylations, the choice of alkynylation reagent played a critical role. On their continuous research interest for alkynes synthesis, Li group reported a versatile catalytic system comprising of dicationic iridium catalyst and electrophilic alkynylation reagent for the ortho C−H alkynylation of carbonyl compounds (Scheme ). Heterocycles including furan and oxazole, proceed smoothly in this ortho C−H alkynylation, and regioselective C4−H alkynylation of C3‐ester indoles was also realized.…”

An Update of N-Tosylhydrazones: Versatile Reagents for Metal-Catalyzed and Metal-Free Coupling Reactions

“…In 2014, Jiang and co-workers reported an elegant divergent oxidative alkynylation of ketone-derived hydrazones that gave various internal alkynes and diynes in the presence of CuCl, DABCO, and DMSO at 100 °C under O 2 (1 atm) (Scheme 38). 74 The internal alkynes were generated from the direct dehydration of α-substituted N-tosylhydrazones (path a) or the cross-coupling reaction of methyl ketone derived N-tosylhydrazones (path b1). The alkyne-coordinated copper intermediates T43 generated in situ (R 2 = H) go through a cross-coupling or homocoupling reaction to deliver the corresponding conjugated diynes via paths b2 and b3, respectively.…”