Tandem Cyclization in Ruthenium Vinylidene Complexes with Two Ester Groups

et al. 2016

Self Cite

In an investigation into the chemical reactions of N-propargyl pyrroles 1 a-c, containing aldehyde, keto, and ester groups on the pyrrole ring, with [Ru]-Cl ([Ru]=Cp(PPh3 )2 Ru; Cp=C5 H5 ), an aldehyde group in the pyrrole ring is found to play a crucial role in stimulating the cyclization reaction. The reaction of 1 a, containing an aldehyde group, with [Ru]-Cl in the presence of NH4 PF6 yields the vinylidene complex 2 a, which further reacts with allyl amine to give the carbene complex 6 a with a pyrrolizine group. However, if 1 a is first reacted with allyl amine to yield the iminenyne 8 a, then the reaction of 8 a with [Ru]-Cl in the presence of NH4 PF6 yields the ruthenium complex 9 a, containing a cationic pyrrolopyrazinium group, which has been fully characterized by XRD analysis. These results can be adequately explained by coordination of the triple bond of the propargyl group to the ruthenium metal center first, followed by two processes, that is, formation of a vinylidene intermediate or direct nucleophilic attack. Additionally, the deprotonation of 2 a by R4 NOH yields the neutral acetylide complex 3 a. In the presence of NH4 PF6 , the attempted alkylation of 3 a resulted in the formation the Fischer-type amino-carbene complex 5 a as a result of the presence of NH3, which served as a nucleophile. With KPF6, the alkylation of 3 a with ethyl and benzyl bromoacetates afforded the disubstituted vinylidene complexes 10 a and 11 a, containing ester groups, which underwent deprotonation reactions to give the furyl complexes 12 a and 13 a, respectively. For 13 a, containing an O-benzyl group, subsequent 1,3-migration of the benzyl group was observed to yield product 14 a with a lactone unit. Similar reactivity was not observed for the corresponding N-propargyl pyrroles 1 b and 1 c, which contained keto and ester groups, respectively, on the pyrrole ring.

Section: Alkylation Versus Nucleophilic Additionmentioning

confidence: 60%

“…The 31 P NMR spectrum of complex 14 a displays two doublet resonances at δ= 51.2 and 50.7 ppm, with 2 J (P,P)=35.6 Hz. We recently observed an interesting tandem cyclization of a vinylidene complex containing two adjacent ester groups induced by deprotonation to yield a three‐ring system . However, no similar reaction was observed for 10 a .…”

Section: Resultsmentioning

confidence: 99%

Reactions of a Ruthenium Complex with Substituted N‐Propargyl Pyrroles

Chia

Huang

et al. 2016

Self Cite

“…In the 1 H NMR spectrum, the two doublet resonances at δ =4.36 and 4.26 ppm with 2 J (H,H) = 19.3 Hz are assigned to two hydrogen atoms of C β H 2 because of the nearby stereogenic sp 3 carbon. In the 31 P NMR spectrum, two doublets appear at δ =45.86 and 44.41 ppm with 2 J (P,P)=30.8 Hz 23. However, in the absence of MeOH, the reaction of 10 with HBF 4 in CH 2 Cl 2 affords the fluorine‐substituted bicyclic oxacarbene complex 13 .…”

Section: Resultsmentioning

confidence: 99%

“…In the 31 P NMR spectrum, two doublets appear at d = 45.86 and 44.41 ppm with 2 J-A C H T U N G T R E N N U N G (P,P) = 30.8 Hz. [23] However, in the absence of MeOH, the reaction of 10 with HBF 4 in CH 2 Cl 2 affords the fluorine-substituted bicyclic oxacarbene complex 13. Namely, fluorine is added to the carbocationic site to yield 13.…”

Section: Ring Expansion Using Epoxidesmentioning

confidence: 99%

Reactions of Propargyl Compounds Containing a Cyclobutyl Group Induced by a Ruthenium Complex

Wang

Lin

2012

Reactions of [Ru]Cl ([Ru] = {Cp(PPh(3))(2)Ru}; Cp = cyclopentadienyl) with three alkynyl compounds, 1, 5, and 8, each containing a cyclobutyl group, are explored. For 1, the reaction gives the vinylidene complex 2, with a cyclobutylidene group, through dehydration at C(δ)H and C(γ)OH. With an additional methylene group, compound 5 reacts with [Ru]Cl to afford the cyclic oxacarbene complex 6. The reaction proceeds via a vinylidene intermediate followed by an intramolecular cyclization reaction through nucleophilic addition of the hydroxy group onto C(α) of the vinylidene ligand. Deprotonation of 2 with NaOMe produces the acetylide complex 3 and alkylations of 3 by allyl iodide, methyl iodide, and ethyl iodoacetate generate 4 a-c, respectively, each with a stable cyclobutyl group. Dehydration of 1 is catalyzed by the cationic ruthenium acetonitrile complex at 70 °C to form the 1,3-enyne 7. The epoxidation reaction of the double bond of 7 yields oxirane 8. Ring expansion of the cyclobutyl group of 8 is readily induced by the acidic salt NH(4)PF(6) to afford the 2-ethynyl-substituted cyclopentanone 9. The same ring expansion is also seen in the reaction of [Ru]Cl with 8 in CH(2)Cl(2), affording the vinylidene complex 10, which can also be obtained from 9 and [Ru]Cl. However, in MeOH, the same reaction of [Ru]Cl with 8 affords the bicyclic oxacarbene complex 12 a through an additional cyclization reaction. Transformation of 10 into 12 a is readily achieved in MeOH/HBF(4), but, in MeOH alone, acetylide complex 11 is produced from 10. In the absence of MeOH, cyclization of 10, induced by HBF(4), is followed by fluorination to afford complex 13. Crystal structures of 6 and 12 a' were determined by single-crystal diffraction analysis.

“…Various transition metals, such as titanium, vanadium, chromium, manganese, and iron, have all been utilized to form carbene complexes or that with even higher unsaturated carbon chains, the structure characteristics and chemical reactivities of the resulted complexes have been studied as well. Complexes of the second period transition metals, such as ruthenium carbenes, vinylidenes,, and allenylidienes, were also synthesized and characterized in recent years. Different kinds of metal cumulenes were synthesized by modified organic precursors, particularly alkyne and enyne compounds.…”

Section: Introductionmentioning

confidence: 99%

Reactions of Ruthenium Complexes Containing Pentatetraenylidene Ligand

Tsai

Lin

2016

Self Cite

Two ruthenium acetylide complexes [Ru]-C≡C-C≡C-C(OR)(C H ) (2, R=H and 2 a, R=CH ; [Ru]=Cp(PPh ) Ru) each with two cyclopropyl rings were synthesized from TMS-C≡C-C≡C-C(OH)(C H ) (1; TMS=trimethylsilyl). Treatments of 2 and 2 a with allyl halide in the presence of KPF afforded the vinylidene complexes 3 and 3 a, respectively. When NH PF was used, instead of KPF , additional ring-opening reaction took place on one of the three-membered ring. Treatment of [Ru]Cl with 1,3-butadiyne (6), bearing an epoxide ring, afforded acetylide complex 7 with a furyl ring. Treatment of 2 a with Ph CPF presumably afforded pentatetraenylidene complex {[Ru]=C=C=C=C=C(C H ) }[PF ] (10), which was not isolated. Additions of various alcohols in a solution of 10 generated a number of disubstituted allenylidene complexes {[Ru]=C=C=C(OR)-C=C(C H ) }[PF ] (11). Treatment of 11 with K CO afforded the acetylide complex 12 bearing a carbonyl group, characterized by single X-ray diffraction analysis. Addition of a primary amine to 10 caused cleavage of the farthermost C=C bond and several allenylidene complexes {[Ru]=C=C=C(Me)(NHR)}[PF ] (18) were isolated.