Oxidative Annulation of Arenecarboxylic and Acrylic Acids with Alkynes under Ambient Conditions Catalyzed by an Electron‐Deficient Rhodium(III) Complex

Abstract

It has been established that an electron-deficient Cp(E) rhodium(III) complex catalyzes the oxidative [4+2] annulation of substituted arenecarboxylic and acrylic acids with alkynes under ambient conditions (at RT-40 °C, under air) without using excess amounts of substrates to produce the corresponding substituted isocoumarins and α-pyrones in high yields. Minor modification of reaction conditions depending on the coordination ability of alkynes realized the high efficiency.

Recent Advances in Ruthenium(II)‐Catalyzed C−H Bond Activation and Alkyne Annulation Reactions

“…The same annulation reaction was also reported by Miura and co‐workers in 2007 with the comparatively more expensive [Cp*RhCl 2 ] 2 catalyst (1 mol%) using Cu(OAc) 2 ⋅H 2 O (5 mol%) as the co‐catalyst and air as the oxidant . Tanaka and co‐workers reported the same annulation reaction of benzoic acids with alkynes using an electron‐deficient Rh(III) complex under ambient conditions (at room temperature to 40 °C), using AgNTf 2 and Cu(OAc) 2 ⋅H 2 O as the additives . In 2013, Ison and co‐workers developed relatively mild reaction conditions (60 °C, 24 h in CH 3 OH), for the same annulation reaction using (Cp*IrCl 2 ) 2 as the catalyst and AgOAc as the oxidant .…”

A comprehensive overview of directing groups applied in metal-catalysed C–H functionalisation chemistry

“…A Rh catalysed annulation developed by Tanaka also proceeded under very mild conditions ( Scheme 11B ). 144 However, the use of DCM made this protocol environmentally less attractive. The authors classified the used alkynes into three groups depending on their coordination ability to the catalyst and developed three different protocols accordingly.…”

“…Notably, though, the reaction also worked with heteroaromatic acids and methacrylic acids as substrates. 144 …”

Effect of Cp‐Ligand Methylation on Rhodium(III)‐Catalyzed Annulations of Aromatic Carboxylic Acids with Alkynes: Synthesis of Isocoumarins and PAHs for Organic Light‐Emitting Devices

“…[14] Shibata and Tanaka with co-workers showed that the oxidant nature (Cu(II) or Ag(I)) also have a crucial impact on the selectivity in the case of usage of electron-deficient rhodium complex [Cp'RhCl 2 ] 2 (Cp' = 1,3-(COOEt) 2 -C 5 Me 3 ) as a catalyst. [15] In the last decade, efficient catalytic systems with different selectivity based on other transition metal complexes have been also developed. [16,17] Herein we report on the use of the rhodium complexes [Cp*RhCl 2 ] 2 and [CpRhI 2 ] n for the synthesis of π-extended isocoumarins and PAHs using various polyaromatic carboxylic acids (e. g. 1-naphthoic acid, 1-pyrenecarboxylic acid, fluorene-1-carboxylic acid, etc.)…”