Transition-Metal-Free Cross-Coupling of Aryl Halides with Arylstannanes

Abstract

Transition-metal-free LiCl-promoted cross-coupling reactions of tetraphenyltin, trichlorophenyl-, dichlorodiphenyl-, and chlorotriphenylstannanes with aryl halides in DMF provided access to biaryls in good to high yields. Up to four phenyl groups were transferred from the organostannanes substrates. The aryls bearing electron-withdrawing groups in either halides or organotin substrates gave coupling products in higher yields. The methodology has been applied for the efficient synthesis of ipriflavones.

Organozinc‐Mediated Direct C−C Bond Formation via C−N Bond Cleavage of Ammonium Salts

“…Consequently, TM‐free cross‐coupling methods have attracted much attention in recent years . Some elegant direct cross‐coupling reactions between organometallics (R–M) and organohalides (R–Hal) have been developed, in which R–M (such as Mg, Zn, Al, and Sn,) reacts efficiently with various types of organohalides, including R–I, R—Br, and even unreactive R–Cl (Scheme a). The mechanisms of these direct cross‐coupling reactions have been clarified by means of both experimental–– and theoretical methods.…”

“…[1] However,v arious issues remain, including high cost and poor stability of many TM catalysts and ligands, and disposal of the heavy-metalr esidues.C onsequently,T Mfree cross-coupling methods have attracted much attention in recent years. [2] Some elegantd irectc ross-coupling reactions between organometallics (R-M) and organohalides (R-Hal) have been developed, in which R-M (such as Mg, [3] Zn, [4] Al, [5] and Sn, [6] )reacts efficiently with varioustypes of organohalides, including R-I, R-Br,a nd even unreactiveR -Cl (Scheme 1a).Scheme1.Recent developments in TM-free cross-coupling reactions.[a] Dr.Scheme2.Proposed mechanism.Scheme3.Bis-arylation of ammonium compound 1n.Scheme4.Control experiments.…”

Electron‐Catalyzed Cross‐Coupling of Arylboron Compounds with Aryl Iodides

“…Among these, Suzuki–Miyaura coupling, which employs arylboron compounds as arylmetals, is one of the most widely used due to the high stability and high availability of the reagents and the high functional‐group tolerance of the reaction . On the other hand, since our group reported the first electron‐catalyzed cross‐coupling, where aryl Grignard reagents are employed and an electron derived from them instead of a transition metal acts as a catalyst, we and other groups have reported transition‐metal‐free cross‐coupling of arylmetals (Zn/Al/Sn) as well as alkyl‐ and alkynylzinc reagents . Herein, we report for the first time that arylboron compounds can be utilized as aryl nucleophiles in the electron‐catalyzed cross‐coupling with the aid of a zinc reagent such as diethylzinc or zinc chloride/potassium tert ‐butoxide…”

“…of 2 a ; Table , entry 2). Addition of LiCl (1.5 equiv), an effective accelerator in the previous electron‐catalyzed cross‐coupling reactions, led to full conversion of 2 a to give 3 aa in a high yield (Table , entry 3). No reaction took place in the absence of diethylzinc (Table , entry 4).…”

Electron‐Catalyzed Cross‐Coupling of Arylboron Compounds with Aryl Iodides

“…[1] Among these,S uzuki-Miyaura coupling, which employs arylboron compounds as arylmetals,i s one of the most widely used due to the high stability and high availability of the reagents and the high functional-group tolerance of the reaction. [2] On the other hand, since our group reported the first electron-catalyzed cross-coupling, where aryl Grignard reagents are employed and an electron derived from them instead of at ransition metal acts as ac atalyst, [3] we and other groups have reported transitionmetal-free cross-coupling of arylmetals (Zn [4] /Al [5] /Sn [6] )a s well as alkyl- [7] and alkynylzinc [8] reagents. [9,10] Herein, we report for the first time that arylboron compounds can be utilized as aryl nucleophiles in the electron-catalyzed crosscoupling with the aid of az inc reagent such as diethylzinc or zinc chloride/potassium tert-butoxide.…”