Oxidative Annulation of Anilides with Internal Alkynes Using an (Electron‐Deficient η⁵‐Cyclopentadienyl)Rhodium(III) Catalyst Under Ambient Conditions

Abstract

A dinuclear (electron‐deficient η5‐cyclopentadienyl)rhodium(III) complex was synthesized on a preparative scale via the rhodium‐catalyzed cross [2+2+1] cyclotrimerization of silylacetylenes and two alkynyl esters, leading to substituted silylfulvenes, followed by reductive complexation with rhodium(III) chloride in ethanol. The thus obtained dinuclear (electron‐deficient η5‐cyclopentadienyl)rhodium(III) complex is a highly active precatalyst for the oxidative annulation of anilides with internal alkynes under ambient conditions (at room temperature under air). A preference for annulation across electron‐rich substrates over electron‐deficient substrates was observed using this electron‐deficient rhodium(III) complex.

Oxidative Olefination of Anilides with Unactivated Alkenes Catalyzed by an (Electron‐Deficient η5‐Cyclopentadienyl)Rhodium(III) Complex Under Ambient Conditions

“…In order to gain mechanistic insights into the CH bond activation step using the electron‐deficient complex 1 , a deuterium kinetic isotope effect (DKIE) of olefination of 2 a with 3 a was measured 23. The intermolecular competition experiment between 2 a and 2 a ‐[D 5 ] in the presence of 3 a revealed a DKIE value of 3.3 (Scheme ), which is the almost the same value as that of our previously reported oxidative annulation of 1 a with diphenylacetylene (DKIE value=3.5) 17b. A DKIE value, measured by comparing the initial rates obtained from individual reactions of 2 a and 2 a ‐[D 5 ] with 3 a , was 2.8 (Scheme ).…”

Rhodium(III)‐Catalyzed Tandem [2+2+2] Annulation–Lactamization of Anilides with Two Alkynoates via Cleavage of Two Adjacent C−H or C−H/C−O bonds

“…[4] On the other hand, we have recently reported that the oxidative [3+ +2] annulation of acetanilides with alkynes proceeds at room temperature under air in the presence of catalytic amountso fe lectron-deficient rhodium(III)c omplex [Cp E RhCl 2 ] 2 (1), AgSbF 6 ,and Cu(OAc) 2 . [5,6] In this paper, we have established that an electron-deficientC p E -rhodium(III) complex catalyzes the tandem [2+ +2+ +2] annulation-lactamization of acetanilides with two alkynoates via cleavage of two adjacent CÀHb onds at room temperatureu nder air to give densely substituted banzo[cd]indolones [7] (bottom, Scheme 1). Surprisingly,t he reactions of meta-methoxy-substituted acetanilides with two alkynoates also provided benzo[cd]indolones via unprecedented adjacent CÀH/CÀOb ond cleavage (bottom, Scheme 1).…”

“…Surprisingly,t he reactions of meta-methoxy-substituted acetanilides with two alkynoates also provided benzo[cd]indolones via unprecedented adjacent CÀH/CÀOb ond cleavage (bottom, Scheme 1). [8] In the course of our study of the oxidative [3+ +2] annulation of acetanilides with alkynes using 1 as ap recatalyst, [5] we found that the reaction of 4'-methoxyacetanilide (2a)a nd ethyl 2-butynoate (3a)i na cetonea fforded not indole 4aa but benzo[cd]indolone 5aa as am ajor product ( Table 1, entry 1). The use of CH 2 Cl 2 as as olventa ccelerated the reaction, but led to ac omplex mixture of products.F ortunately,t he use of CH 2 Cl 2 /acetone( 1:1) balancedt he product yield and reaction rate (entry 2).…”

Rh(III)- and Ir(III)-Catalyzed C–C Bond Cross Couplings from C–H Bonds

“…Following this goal, extensive studies have been conducted by Tanaka who investigated the potential of electron-deficient Cp* ligands, bearing two ester substituents [148][149][150]. This complex showed an improved reactivity with regard to electron-rich C-H substrates like acetanilides and benzylic alcohols, enabling a C-H activation/annulation sequence at room temperature and benefiting from air as oxidant.…”