Lanthanide Amide-catalyzed Aza-Henry Reaction of N-Tosyl Imines with Nitroalkanes

In the presence of 10 mol% lanthanide amide [(Me₃Si)₂N]₃Ln(µ‐Cl)Li(THF)₃, the aza‐Henry reaction of N‐tosyl imines with nitroalkanes (1:5 molar ratio) could be performed in good yields. The lanthanide amide‐catalyzed aza‐Henry reaction has the features of mild reaction conditions, tolerance of a variety of aromatic aldehyde‐derived imines and nitroalkanes, short time and good chemical yields. A catalytic mechanism for the reaction was also proposed.     

Synthesis,Structural Characterization,and Catalytic Activity of Scandium,Samarium, and Dysprosium Complexes Supported by Tris(pyrrolyl‐α‐methyl)amine Ligand

The synthesis, structures and catalytic activities of three organolanthanide complexes supported by the H₃tpa ligand (H₃tpa = tris(pyrrolyl‐α‐methyl) amine) are described. Treatment of H₃tpa with one equivalent of Ln[N(SiMe₃)₂]₃ (Ln = Sc, Sm, Dy) in THF gives, after recrystallization from toluene/THF solution, Sc(tpa)(THF)₂ ( 1 ), Sm(tpa)(THF)₃ ( 2 ) and Dy(tpa)(THF)₃ ( 3 ) in good yields. The structures of complexes 1 – 3 were determined by single‐crystal X‐ray diffraction and elemental analysis. Complexes 2 and 3 exhibited good catalytic activity for the polymerization of ?‐caprolactone.     

Ruthenium‐Catalyzed Tandem‐Isomerization/Asymmetric Transfer Hydrogenation of Allylic Alcohols

A one‐pot procedure for the direct conversion of racemic allylic alcohols to enantiomerically enriched saturated alcohols is presented. The tandem‐isomerization/asymmetric transfer hydrogenation process is efficiently catalyzed by [{Ru(p‐cymene)Cl₂}₂] in combination with the α‐amino acid hydroxyamide ligand 1 , and performed under mild conditions in a mixture of ethanol and THF. The saturated alcohol products are isolated in good to excellent chemical yields and in enantiomeric excess up to 93 %.     

Efficient synthesis of polysubstituted pyrrole-3-carbonitriles via reactions of 1,1-dicyano-2,3-diarylcyclopropanes with aromatic imines

Co(ClO₄)₂ smoothly catalyzed the reactions of 1,1-dicyano-2,3-diarylcyclopropanes with aromatic imines to give the novel polysubstituted pyrrole-3-carbonitriles bearing an 2-arylidenimino group in good to high yields in refluxing THF.     

Reductive Coupling of Aldimines Mediated with Samarium Catalyzed by Cp2TiCl2

Reductive coupling of aldimines into vicinal diamines mediated with samarium catalyzed by Cp₂TiCl₂ proceeds in refluxing THF with good yields.     

Cationic palladium complex‐catalyzed carbonylation of 2,3‐dien‐1‐ols to 1,3‐diene‐2‐carboxylic acids and esters under mild conditions

A cationic palladium complex, [Pd(PPh₃)₂(MeCN)₂](BF₄)₂, catalyzed the carbonylation of 2,3‐dien‐1‐ols under mild conditions. The dienols bearing two or more alkyl substituents on the diene part afforded 1,3‐diene‐2‐carboxylic acids successfully in tetrahydrofuran (THF), while those possessing one or no alkyl substituent gave polymers of the products exclusively. The former afforded the corresponding methyl esters in good yields when the reactions were carried out in methanol, while the latter afforded mainly the Diels–Alder reaction products of the resulting esters. An alkylidene group‐substituted π‐allylpalladium species has been presumed to be an intermediate. Copyright © 2000 John Wiley & Sons, Ltd.     

Rhenium-catalyzed synthesis of naphthalene derivatives via insertion of aldehydes into a C-H bond

A rhenium complex, [ReBr(CO)₃(THF)]₂, catalyzed reactions of aromatic ketimines and aldehydes with dienophiles, followed by dehydration, to give naphthalene derivatives in good to excellent yields. This reaction proceeds via C-H bond activation, insertion of an aldehyde, intramolecular nucleophilic cyclization, reductive elimination, elimination of aniline and Diels-Alder reaction. After dehydration, naphthalene derivatives were formed.     

Reductive Elimination of Phenylsulfonyl Groups in the 3‐Position of Benzo[a]heptalene‐2,4‐diols

3‐(Phenylsulfonyl)benzo[a]heptalene‐2,4‐diols 1 can be desulfonylated with an excess of LiAlH₄/MeLi?LiBr in boiling THF in good yields (Scheme 6). When the reaction is run with LiAlH₄/MeLi, mainly the 3,3′‐disulfides 6 of the corresponding 2,4‐dihydroxybenzo[a]heptalene‐3‐thiols are formed after workup (Scheme 7). However, the best yields of desulfonylated products are obtained when the 2,4‐dimethoxy‐substituted benzo[a]heptalenes 2 are reduced with an excess of LiAlH₄/TiCl₄ at ?78→20° in THF (Scheme 10). Attempts to substitute the PhSO₂ group of 2 with freshly prepared MeONa in boiling THF led to a highly selective ether cleavage of the 4‐MeO group, rather than to desulfonylation (Scheme 13).     

Reactivity of mixed organozinc and mixed organocopper reagents: 11. Nickel‐catalyzed atom‐economic aryl–allyl coupling of mixed (n‐alkyl)(aryl)zincs

Group selectivity in the allylation of mixed (n‐butyl)(phenyl)zinc reagent can be controlled by changing reaction parameters. CuCN‐catalyzed allylation in tetrahydrofuran (THF)–hexamethylphosphoric triamide is n‐butyl selective and also γ‐selective in the presence of MgCl₂, whereas CuI‐catalyzed allylation in THF in the presence of n‐Bu₃P takes place with a n‐butyl transfer:phenyl transfer ratio of 23:77 and an α:γ transfer ratio of phenyl of 76:24. NiCl₂(Ph₃P)₂‐catalyzed allylation in the presence of LiCl is phenyl selective with an α:γ ratio of 65:35. The reaction of methyl‐ or n‐butyl(aryl)zinc reagents with an allylic electrophile in THF at room temperature in the presence of NiCl₂(Ph₃P)₂ catalyst and LiCl as an additive provides an atom‐economic alternative to aryl–allyl coupling using diarylzincs. Copyright © 2014 John Wiley & Sons, Ltd.     

Synthesis and Structural Characterization of Lanthanide Amides Stabilized by an N-Aryloxo Functionalized β-Ketoiminate Ligand

The synthesis and characterization of dimeric lanthanide amides stabilized by a dianionic N‐aryloxo functionalized β‐ketoiminate ligand are described in this paper. Reactions of 4‐(2‐hydroxy‐5‐tert‐butyl‐phenyl)imino‐2‐pentanone (LH₂) with Ln[N(SiMe₃)₂]₃(µ‐Cl)Li(THF)₃ in a 1:1 molar ratio in THF gave the dimeric lanthanide amido complexes [LLn{N(SiMe₃)₂}(THF)]₂ [Ln=Nd ( 1 ), Sm ( 2 ), Yb ( 3 ), Y ( 4 )] in good isolated yields. These complexes were characterized by IR spectroscopy, elemental analysis, and ¹H NMR spectroscopy in the case of complex 4 . The definitive molecular structures of complexes 1 , 3 , and 4 were determined. It was found that complexes 1 to 4 can initiate the ring‐opening polymerization of L‐lactide.     

Facile Synthesis and Palladium‐Catalyzed Cross‐Coupling Reactions of 2,3‐Bis(pinacolatoboryl)‐1,3‐butadiene

Treatment of 1,1‐bis(pinacolatoboryl)ethene with an excess of 1‐bromo‐1‐lithioethene gave 2,3‐bis(pinacolatoboryl)‐1,3‐butadiene in high yield. Palladium‐catalyzed cross‐coupling of the resulting diborylbutadiene with aryl iodides took place smoothly in the presence of a catalytic amount of Pd(OAc)₂/PPh₃ and aqueous KOH to give 2,3‐diaryl‐1,3‐butadienes in good yields. The coupling reaction with commercially available 4‐acetoxyphenylmethyl chloride under the same conditions followed by hydrolysis of the acetyl groups gave anolignan B in a one‐pot manner. A variety of [3]‐ to [6]dendralenes were synthesized by palladium‐catalyzed coupling of the diene or 1,1‐bis(pinacolato)borylethene with alkenyl or dienyl halides, respectively, in good yields.     

Catalytic Divergent [3+3]‐ and [3+2]‐Cycloaddition by Discrimination Between Diazo Compounds

Highly selective divergent cycloaddition reactions of enoldiazo compounds and α‐diazocarboximides catalyzed by copper(I) or dirhodium(II) have been developed. With tetrakis(acetonitrile)copper(I) tetrafluoroborate as the catalyst epoxypyrrolo[1,2‐a]azepine derivatives were prepared in good yields and excellent diastereoselectivities through the first reported [3+3]‐cycloaddition of a carbonyl ylide. Use of Rh₂(pfb)₄ or Rh₂(esp)₂ directs the reactants to regioselective [3+2]‐cycloaddition generating cyclopenta[2,3]pyrrolo[2,1‐b]oxazoles with good yields and excellent diastereoselectivities.     

Four‐Component,One‐Pot Synthesis of 1,4‐Disubstituted 1,2,3‐Triazoles Bearing 1‐(2‐Phenylselenocyclohexyl) Group

An efficient, one‐pot, three‐step, regioselective synthesis of 4‐substituted 1‐(2‐phenylselenocyclohexyl)‐1,2,3‐triazoles, involving in situ generation of l‐azido‐2‐phenylselenocyclohexane has been developed via four‐component reaction of phenylselenenyl bromide, cyclohexene, sodium azide and terminal alkynes catalyzed by copper iodide in a mixture of DMF/THF (1:1) at room temperature under mild conditions with simple workup and good yields.     

Phenylene‐bridged β‐Ketoiminate Dilanthanide Aryloxides: Synthesis,Structure, and Catalytic Activity for Addition of Amines to Carbodiimides

The synthesis and reactivity of a series of bimetallic lanthanide aryloxides stabilized by a p‐phenylene‐bridged bis(β‐ketoiminate) ligand is presented. The reaction of 1,4‐diaminobenzene with acetylacetone in a 1:2.5 molar ratio in absolute ethanol gave the compound 1,4‐bis(4‐imino‐2‐pentanone)benzene ( 1 ) (LH₂) in high yield. Compound 1 reacted with (ArO)₃Ln(THF)₂ (ArO = 2,6‐tBu₂‐4‐MeC₆H₂O, THF = tetrahydrofuran) in a 1:2 molar ratio in THF, after workup, to give the corresponding dilanthanide aryloxides L[Ln(OAr)₂(THF)]₂ [Ln = Yb ( 2 ), Y ( 3 ), Sm ( 4 ), Nd ( 5 ), La ( 6 )] in high isolated yields. Compound 1 and complexes 2 – 6 were fully characterized, including X‐ray crystal structure analyses for complexes 2 , 3 , 5 , and 6 . Complexes 2 – 6 can be used as efficient pre‐catalysts for catalytic addition of amines to carbodiimides, and the ionic radii of the central metal atoms have a significant effect on the catalytic activity with the increasing sequence of La ( 6 ) < Nd ( 5 ) ≈ Sm ( 4 ) < Y ( 3 ) ≈ Yb ( 2 ). The catalytic addition reaction with 2 showed a good scope of substrates including primary and secondary amines.     

Palladium‐Catalyzed Annulation of 1,2‐Diborylalkenes and ‐Arenes with 1‐Bromo‐2‐[(Z)‐2‐bromoethenyl]arenes: A Modular Approach to Multisubstituted Naphthalenes and Fused Phenanthrenes

(Z)‐1,2‐Diaryl‐1,2‐bis(pinacolatoboryl)ethenes underwent double‐cross‐coupling reactions with 1‐bromo‐2‐[(Z)‐2‐bromoethenyl]arenes in the presence of [Pd(PPh₃)₄] as a catalyst and 3 M aqueous Cs₂CO₃ as a base in THF at 80 °C. The double‐coupling reaction gave multisubstituted naphthalenes in good to high yields. Annulation of 1,2‐bis(pinacolatoboryl)arenes with bromo(bromoethenyl)arenes in the presence of a catalyst system that consisted of [Pd₂(dba)₃] (dba=dibenzylideneacetone) and 2‐dicyclohexylphosphino‐2′,6′‐dimethoxybiphenyl (SPhos) under the same conditions produced fused phenanthrenes in good to high yields. The first annulation coupling occurred regiospecifically at the bromoethenyl moiety. This procedure is applicable to the facile synthesis of polysubstituted anthracenes, benzothiophenes, and dibenzoanthracenes through a double annulation pathway by using the corresponding dibromobis[(Z)‐2‐bromoethenyl]benzenes as diboryl coupling partners.     

Polymerization of n‐phenyl maleimide by lanthanide complexes

N‐Phenyl maleimide (N‐PMI) was successfully polymerized by divalent rare‐earth complexes (ArO)₂Sm(THF)₄ (ArO = 2,6‐di‐tert‐butyl‐4‐methyl phenoxo‐; THF = tetrahydrofuran) and (Ar′O)₂Ln(THF)₃ (Ar′O = 2,6‐di‐tert‐butyl phenoxo‐; Ln = Sm, Yb, or Eu). The central metals greatly affected the reactivity, and the reactivity order was Sm(II) > Yb(II) > Eu(II). The activity of (Ar′O)₂Sm(THF)₃ was higher than that of (ArO)₂Sm(THF)₄. The polymerization yields were higher in THF than in other solvents, and the maximum yields were obtained around 25 °C. A proposed mechanism is discussed. © 2005 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 43: 3966–3972, 2005     

Synthesis of ferrocene‐containing N‐aryloxo β‐ketoiminate lanthanide complexes and polymerization of ε‐caprolactone

The synthesis, characterization and ε‐caprolactone polymerization behavior of lanthanide amido complexes stabilized by ferrocene‐containing N‐aryloxo functionalized β‐ketoiminate ligand FcCOCH₂C(Me)N(2‐HO‐5‐Bu^t‐C₆H₃) (LH₂, Fc = ferrocenyl) are described. The lanthanide amido complexes [LLnN(SiMe₃)₂(THF)]₂ [Ln = Nd ( 1 ), Sm ( 2 ), Yb ( 3 ), Y ( 4 )] were synthesized in good yields by the amine elimination reactions of LH₂ with Ln[N(SiMe₃)₂]₃(µ‐Cl)Li(THF)₃ in a 1:1 molar ratio in THF. These complexes were characterized by IR spectroscopy and elemental analysis, and ¹H NMR spectroscopy was added for the analysis of complex 4 . The definitive molecular structures of complexes 1 and 3 were determined by X‐ray diffraction studies. Complexes 1 – 4 can initiate the ring‐opening polymerization of ε‐caprolactone with moderate activity. Copyright © 2011 John Wiley & Sons, Ltd.     

Azirine/Oxindole Ring Enlargement via Amidinium Intermediates

A novel general method for the synthesis of oxindoles, namely the ‘azirine/oxindole ring enlargement via amidinium‐intermediates’ has been established: the reaction of 2H‐azirin‐3‐amines 1 with BF₃?OEt₂ in THF solution at ?78° leads to 1,3,3‐trialkyl‐2‐amino‐3H‐indolium tetrafluoroborates 14 in good yields (Scheme 5). Treatment of aqueous solutions of 14 at 0° with aqueous NaOH (30%) and extraction with CH₂Cl₂ gives oily substances that are either hydrates of 1,3,3‐trialkyl‐2‐dihydroindol‐2‐imines 15 or the corresponding indolium hydroxides. These products are transformed to the corresponding 1,3,3‐trialkyl‐2,3‐dihydroindol‐2‐ones 17 in modest yields upon refluxing in H₂O/THF. Reaction of 14 with Ac₂O in pyridine at ca. 23° for 16 h followed by aqueous workup and chromatographic separation leads to mixtures of N‐(1,3,3‐trialkyl‐2,3‐dihydro‐indol‐2‐yliden)acetamides 16 and oxindoles 17 (Scheme 6). Hydrolysis of 16 with aqueous HCl under reflux for 1–2 h gives oxindoles 17 in a good yield. Several oxindoles, spiro‐oxindoles, and 5‐substituted oxindoles were synthesized by means of the reactions mentioned above.     

Lanthanide amides [(Me3Si)2N]3Ln(µ‐Cl)Li(THF)3‐catalyzed phospho‐aldol‐brook rearrangement reaction of dialkyl phosphites with isatins

The tetracoordinated lanthanide amides [(Me₃Si)₂N]₃Ln(µ‐Cl)Li(THF)₃ were found to serve as highly active catalysts for the phospho‐Aldol‐Brook rearrangement reaction of various dialkyl phosphites and isatins. The reactions produced dialkyl 2‐oxoindolin‐3‐yl phosphates in good to excellent yields in the presence of 1 mol% [(Me₃Si)₂N]₃La(µ‐Cl)Li(THF)₃ at room temperature within 5 min. A mechanism for this highly efficient process was proposed. © 2012 Wiley Periodicals, Inc. Heteroatom Chem 23:449–456, 2012; View this article online at wileyonlinelibrary.com . DOI 10.1002/hc.21036     

A novel synthetic method for preparation of some folates

An improved method was developed for preparation of 5,6,7,8-tetrahydrofolic acid (THF) and calcium-5-methyltetrahydrofolate (5-MTHF-Ca) by reduction of folic acid using KBH₄ catalyzed by Pb(NO₃)₂. The yields of THF and 5-MTHF-Ca were 56.5 and 42.7 %, respectively. A convenient method for measurement of THF and 5-MTHF-Ca using liquid chromatography–mass spectrometry (LC–MS) was also established, enabling analysis of those folates within 10 min without application of gradient elution.