Iridium‐Catalyzed [2+2+2] Cycloaddition of α,ω‐Diynes with Cyanamides

Abstract

Thec omplex[ Ir(cod)Cl] 2 /DPPF or rac-BINAP is an efficient catalyst for the [2+ +2+ +2] cycloaddition of a,w-diynesw ith cyanamides.Awide range of cyanamides derived from secondary amines are good coupling partners for a,w-diynes. Ther eaction of unsymmetrical a,w-diynes possessingt wo different internal alkyne moieties with cyanamides is regioselective.Ac ompetitive experiment showed that cyanamide is more reactive than nitrile. This higher reactivity of cyanamide than nitrile was analyzed based on density functional theory (DFT)c alculations at the B3LYP level.

Synthesis of Anthraquinones by Iridium-Catalyzed [2 + 2 + 2] Cycloaddition of a 1,2-Bis(propiolyl)benzene Derivative with Alkynes

“…While PPh3, 2,2'bis(diphenylphosphino)biphenyl (BIPHEP), and DPPF were ineffective at catalyzing the formation of fluorenone 5j (Yield 28% to 63%, entries 2 to 4), excellent yield was realized with the use of 1,2bis[bis(pentafluorophenyl)phosphino]ethane (F-DPPE) (Yield 94%, entry 5). Based on our previous results [45,46,48,49], we envision that the catalytic reaction is initiated by the coordination of diyne 1 to the iridium(I) complex. Oxidative addition of diyne 1 to an iridium(I) complex forms iridacyclopentadiene [51][52][53][54].…”

“…Sufficient yield was achieved with the use of 1,2-bis(diphenylphosphino)ethane (DPPE) as a ligand to give 83% yield of anthraquinone 3a (entry 3), while other representative bidentate phosphine ligands such as 1,3-bis(diphenylphosphino)propane (DPPP), 1,4-bis(diphenylphosphino)butane (DPPB), and 1,1 -bis(diphenylphosphino)ferrocene (DPPF) were ineffective at achieving a high yield (Yield 22% to 45%, entries 4 to 6). with alkynes, nitriles, and isocyanate to provide a variety of aromatic carbocycles and heterocycles [42][43][44][45][46][47][48][49][50]. In the course of our ongoing investigation into iridium-catalyzed [2 + 2 + 2] cycloaddition, we found that an iridium/bisphosphine catalytic system catalyzed the [2 + 2 + 2] cycloaddition of 1,2bis(propiolyl)benzene derivatives to provide anthraquinones bearing a variety of substituents in an atom-economical manner.…”

Regioselectivity in the Iridium-Catalyzed [2 + 2 + 2] Cycloaddition of Unsymmetrical α,ω-Diynes with Nitrile: A DFT Study

“…The highest occupied (HO) MO of the iridacyclopentadiene fragment in IIs (Figure 6a) is responsible for the electron delocalization from the iridacyclopentadiene fragment to nitrile. 13 The weight of the C 1 atom in the orbital is 0.223, which is larger than that of the C 4 atom, 0.208, because of the out-of-phase overlap between the Ir atom and the chlorine atom. 30 Not only the σ-donating ability but also the existence of a pπ-orbital of the chloride ligand also affects the difference in reactivity between the two α-carbon atoms (C 1 and C 4 ).…”

“…11 The difference in reactivity between cyanamide and nitrile was also discussed in terms of orbital interactions. 13 Some other groups theoretically determined the mechanism via iridacyclopentadienes for iridium-catalyzed cycloaddition. 16−19 In the present study, we carried out DFT calculations to elucidate the origin of the regioselectivity in the iridiumcatalyzed cycloaddition of a nitrile with an α,ω-unsymmetrical diyne.…”

Recent Advances in Cyanamide Chemistry: Synthesis and Applications

“…Takeuchi and co-workers found [Ir(cod)Cl] 2 /BINAP as an efficient catalyst for the [2 + 2 + 2] cycloaddition of α,ω-diynes 54 with cyanamide nitriles ( Scheme 13 e). The authors argue that the presence of a phosphine-ligand-offered flexibility with respect to the catalytic activity, which could be achieved by choosing the appropriate phosphine ligand [ 27 ].…”