Diverse Reactivity of Zirconacyclocumulenes Derived from Coupling of Benzynezirconocenes with 1,3‐Butadiynes towards Acyl Cyanides: Synthesis of Indeno[2,1‐<i>b</i>]pyrroles or [3]Cumulenones

An efficient multicomponent synthesis of 5-azaindoles and dihydropyrrolo[3,2-c]azepines was achieved by zirconocene-mediated coupling of silicon-tethered diynes, nitriles, and isocyanides. The synthesis, structures, and intramolecular cyclization of mono- and bis(iminoacyl)--Zr intermediates were investigated to elucidate the reaction process. Upon hydrolysis, the isolated mono(iminoacyl)--Zr intermediates underwent intramolecular cyclization to afford tetrasubstituted 5-azaindoles, whereas intramolecular cyclization of bis(iminoacyl)--Zr intermediates led to the formation of dihydropyrrolo[3,2-c]azepines. The structure of a bis(iminoacyl)--Zr intermediate, formed through insertion of two molecules of CyNC into the Zr--C bond, and structures of two dihydropyrrolo[3,2-c]azepines were characterized by single-crystal X-ray structural analysis.

Section: Resultsmentioning

confidence: 56%

Efficient One‐Pot Synthesis of N‐Containing Heterocycles by Multicomponent Coupling of Silicon‐Tethered Diynes, Nitriles, and Isocyanides through Intramolecular Cyclization of IminoacylZr Intermediates

Zhang

2010

“…The results indicated that a CN group reacts preferentially with zirconacycle 2 / 3 at the initial step. The reaction pattern is quite different compared with that of the reactions of aroyl cyanides with seven‐membered zirconacyclocumulenes, which were prepared by coupling of benzynezirconocene with butadiynes 7c. In those reactions, a carbonyl group reacted preferentially with a propargyl zirconium moiety.…”

Section: Methodsmentioning

confidence: 96%

“…7a An S E 2′‐type addition of the CN group of carbamoyl cyanides to the less hindered propargyl zirconium moiety in complex 2 takes place to deliver an azazirconacyclocumulene 8 , which might isomerize to azazirconacyclopentadiene 10 ; however, we still cannot exclude the reaction pathway for 10 involving direct insertion of a cyano group into the ZrC

_{sp^{2}}

bond close to the R 1 group of 2 17. As a minor reaction pathway, addition of the CO group of carbamoyl cyanides to zirconacycle 2 / 3 affords either cyano‐substituted oxazirconacycle 9 or 11 ; hydrolysis of 11 gives enynyl amide 5 through elimination of a cyano group 7c. Attack of the nitrogen lone pair in intermediate 10 to the CN moiety of a second molecule of carbamoyl cyanide followed by intramolecular nucleophilic addition provides fused oxirane intermediate 13 ;18 ring opening of the oxirane by the electron‐rich N ‐phenyl ring leads to intermediate 14 , CC bond fragmentation followed by a 1,3‐hydrogen shift furnishes the final product 4 .…”

Section: Methodsmentioning

confidence: 99%

Unexpected Zirconium‐Mediated Multicomponent Reactions of Conjugated 1,3‐Butadiynes and Monoynes with Acyl Cyanide Derivatives

You

Liu

2012

Self Cite

“…diene complexes 2 and the allenyl-aza-zirconacycles 3 were thus generated in high yields from tBuCN, a different nitrile RCN, a Si-tethered diyne, and the zirconocene species. [14][15][16][17] We believe that these two reactive organometallic intermediates 2 and 3 should be synthetically useful for the synthesis of heterocyclic compounds. Indeed in this work, as shown in Scheme 2, further reactions of these intermediates with nitriles were found to proceed smoothly through interesting insertions and skeletal rearrangements, providing useful synthetic methods for N-containing heterocyclic compounds.…”

Section: Introductionmentioning

confidence: 99%

One‐Pot Selective Syntheses of 5‐Azaindoles through Zirconocene‐Mediated Multicomponent Reactions with Three Different Nitrile Components and One Alkyne Component

Zhang

Zhao

et al. 2011

5-Azaindoles either with three different substituents at their 2-, 4-, and 6-positions or with two identical substituents at their 2- and 6-positions and a different one at the 4-position, were obtained in good to excellent isolated yields by a zirconocene-mediated multicomponent process. Each reaction involved four organic partners, comprising a Si-tethered diyne, one tBuCN component, and two (either different or identical) nitriles. All these four components were combined through the action of a Cp(2)Zr(II) species into a three-ring fused Zr/Si-containing organometallic complex in a perfectly chemo- and regioselective manner. This multicomponent reaction process consisted of three reaction steps, all of which were made clear through the isolation and characterization of their corresponding organometallic intermediates: the zirconacyclopropene-azasilacyclopentadienes 2, the allenyl-aza-zirconacycles 3, and the three-ring fused complexes 6. X-ray single-crystal structural analyses of two three-ring fused Zr/Si-containing intermediates and two 5-azaindoles unambiguously showed the positions of the different substituents and the regioselectivity. Iminopyrrole derivatives could be also highly selectively prepared from a Si-tethered diyne and two different nitriles.