Double elimination protocol for synthesis of 5,6,11,12-tetradehydrodibenzo[a,e]cyclooctene

A new method for constructing 5,6,11,12-tetradehydrodibenzo[a,e]cyclooctene is described on the basis of one-pot double elimination protocol. The target molecule, which is the smallest cyclophane with alternate arylene-ethynylene linkage, is synthesized in 61 % yield through oxidative dimerization of ortho-(phenylsulfonylmethyl)benzaldehyde. The initial carbon-carbon bond formation between sp(3) carbons followed by stepwise conversion to sp(2) and finally sp carbons bypasses the difficulty encountered in direct coupling of the sp carbon in the terminal acetylene. The mechanism of this process is discussed. The Wittig-Horner-type coupling is a key reaction employed for the carbon-carbon bond formation. Generation of (E)-vinylsulfone moiety in the first coupling between alpha-sulfonyl anion and aldehyde functions is crucial for the effective second coupling to complete the cyclization. The syn-elimination of the (E)-vinylsulfone moieties in the cyclized intermediate furnishes the acetylenic bonds.     

Silver(I) complex of 5,6,11,12-tetradehydrodibenzo[a,e]cyclooctene

The reaction of 5,6,11,12-tetradehydrodibenzo[a,e]cyclooctene with silver(I)triflate yielded a 1:2 complex. X-ray investigations revealed that each silver ion is tetrahedrally coordinated to one triple bond and three oxygen atoms of the triflate anion.     

Gas-phase conformations and exciton couplings in 5,6,11,12-tetrahydrodibenzo[a,e]cyclooctene

The conformations and exciton couplings in 5,6,11,12-tetrahydrodibenzo[a,e]cyclooctene (THDC) have been studied using resonance-enhanced two-photon ionization spectroscopy in a supersonic jet expansion. It has been estimated from the spectral analysis that 90% of THDC exists in the twist-boat (TB) conformation; the chair (C) conformer constitutes the remaining 10%. Most of the vibronic activity in the spectrum of THDC is associated with the symmetric flapping of the aromatic rings of the TB conformer. The observed S₁/S₂ exciton splitting of the TB conformer is 100 cm^?1. The S₁/S₂ transition of the C conformer is found to be forbidden. The exciton splittings of the C and TB conformers were estimated by the spectral analysis of two deuterated isotopomers of THDC. The estimated exciton splittings of the C and TB conformers are 14.7 and 101.9 cm^?1, respectively. The supramolecular model of bichromophores with identical chromophores at the CIS/6-31+G(d)//HF/6-31+G(d) level of theory predicted electronic coupling energies that are very close to the experimental exciton coupling energies.     

Intramolecular Pauson-Khand reactions of methylenecyclopropane and bicyclopropylidene derivatives as an approach to spiro(cyclopropanebicyclo[n.3.0]alkenones)

The trimethylsilyl-protected enynes 9a-c and 14a,b with alkynyl substituents on the three-membered ring or on the double bond of a methylenecyclopropane or a bicyclopropylidene moiety were prepared in two steps from the alcohols 6a-c and 12a,b, respectively, by conversion to the iodides and their coupling with lithium (trimethylsilyl)acetylide (8) in 38-73% overall yields. The bicyclopropylidene derivative 9d was synthesized in 49% yield directly from bicyclopropylidene (3) by lithiation followed by coupling with (5-iodopent-1-ynyl)trimethylsilane (11). Enynes 9b-d were protiodesilylated by treatment with K2CO3 in methanol to give the corresponding unprotected enynes 10b-d in 53, 74 and 94% yield, respectively. Enynes 17a-c with a carbonyl group adjacent to the acetylenic moiety were synthesized from oxo derivatives 15a-c by Wittig olefination followed by coupling with 8 in 47, 18 and 12% overall yield, respectively. Pauson-Khand reactions of the methylenecyclopropane derivatives with a substituent on the ring (9a,b and 10a) as well as on the double bond (14a,b and their in situ prepared protiodesilylated analogues) proceeded smoothly by stirring of the corresponding enyne with [Co2(CO)8] in dichloromethane at ambient temperature followed by treatment of the formed complexes with trimethylamine N-oxide under an oxygen atmosphere at -78 degrees C to give tricyclic or spirocyclopropanated bicyclic enones 18a,b, 19a, 20a,b, 21a,b in good yields. Alkynylbicyclopropylidene derivatives 9c,d and 10c,d formed the corresponding cobalt complexes at -78 to -20 degrees C. Treatment of the latter with N-methylmorpholine N-oxide under an argon atmosphere at -20 degrees C gave the spirocyclopropanated tricyclic enones 18c, 19c and 18d in 31-45% yields. The structure of 19c was proved by X-ray crystal structure analysis. The cyclization of enynones 17a-c in MeCN at 80 degrees C gave the spirocyclopropanated bicyclic diketones 22a-c in 38-65% yields. Intramolecular PKRs of the enynes 25a,d with a chiral auxiliary adjacent to the triple bond gave the corresponding products 26a,d in 70 and 79% yield, respectively, as 5:1 and 8:1 mixtures of diastereomers, respectively. Addition of lithium dimethylcuprate or higher order cuprates to the double bond of the former furnished bridgehead-substituted bicyclo[3.3.0]octanones 27a-c in 57-86% yields. Protiodesilylation of 27a followed by acetal cleavage gave the enantiomerically pure spirocyclopropanated bicyclo[3.3.0]octanedione (1R,5R)- 29a with [alpha]D(20)=-148 (c=1.0 in CHCl3) in 55% overall yield.     

A study of [Co2(alkyne)(binap)(CO)4] complexes (BINAP=(1,1'-binaphthalene)-2,2'-diylbis(diphenylphosphine))

Understanding the interaction of chiral ligands, alkynes, and alkenes with cobaltcarbonyl sources is critical to learning more about the mechanism of the catalytic, asymmetric Pauson-Khand reaction. We have successfully characterized complexes of the type [Co2(alkyne)(binap)(CO)4] (BINAP=(1,1'-binaphthalene)-2,2'-diylbis(diphenylphosphine)) and shown that diastereomer interconversion occurs under Pauson-Khand reaction conditions when alkyne=HC[triple bond]CCO2Me. Attempts to isolate [Co2(alkyne)(binap)(CO)x] complexes with coordinated alkenes led to the formation of cobaltacyclopentadiene species.     

A stable derivative of cyclooctatrienyne: Synthesis and crystal structures of 1,4,7,10-tetramethyl-5,6-didehydrodibenzo[a,e]cyclooctene and 1,4,7,10-tetramethyldibenzo[a,e]cyclooctene

A stable derivative of cyclooctatrienyne (1), namely 1,4,7,10-tetramethyl-5,6-didehydrodibenzo-[a,e]cyclooctene (3), has been synthesized and fully characterized. X-Ray crystallographic analyses indicate that 3 adopts a “butterfly” conformation intermediate between those of virtually planar 5,6-didehydrodibenzo-[a,e]cyclooctene (2) and tub-shaped 1,4,7,10-tetramethyldibenzo[a,e]cyclooctene(16). The methyl substituents effectively shield the otherwise rather exposed strained triple bond of 3 and kinetically stabilize it against dimerization and/or air oxidation.     

Synthesis of 1,4-Cyclohexadiene Carboxylates through a Formal [2+4]-Cycloaddition of Propiolates under Cobalt Catalysis

A low-valent cobalt(I) complex, formed from the reduction of CoBr₂(dppe) with zinc, acts as catalyst for the efficient [2+4] cycloaddition of β-alkyl, cycloalkyl and aryl substituted propiolates to dienes. This transformation yields synthetically relevant 1,4-cyclohexadiene carboxylates in good to excellent yields. Furthermore, the target compounds are novel lead structures for the discovery of fragrance ingredients from the fruity, floral and spicy odor family.     

Synthesis of Aminopyridines and Aminopyridones by Cobalt‐Catalyzed [2+2+2] Cycloadditions Involving Yne‐Ynamides: Scope,Limitations, and Mechanistic Insights

An in‐depth study of the cobalt‐catalyzed [2+2+2] cycloaddition between yne‐ynamides and nitriles to afford aminopyridines has been carried out. About 30 nitriles exhibiting a broad range of steric demand and electronic properties have been evaluated, some of which open new perspectives in metal‐catalyzed arene formation. In particular, the use of [CpCo(CO)(dmfu)] (dmfu=dimethyl fumarate) as a precatalyst made possible the incorporation of electron‐deficient nitriles into the pyridine core. Modification of the substitution pattern at the yne‐ynamide allows the regioselectivity to be switched toward 3‐ or 4‐aminopyridines. Application of this synthetic methodology to the construction of the aminopyridone framework using a yne‐ynamide and an isocyanate was also briefly examined. DFT computations suggest that 3‐aminopyridines are formed by formal [4+2] cycloaddition between the nitrile and the intermediate cobaltacyclopentadiene, whereas 4‐aminopyridines arise from an insertion pathway.     

Synthesis of Tricyclic Fused 3‐Aminopyridines through Intramolecular CoI‐Catalyzed [2+2+2] Cycloaddition between Ynamides,Nitriles, and Alkynes

Three‐ring circus : An expedient route to tricyclic fused 2‐trimethylsilyl‐3‐aminopyridines exhibiting unprecedented skeletons is described. The key step is a very efficient cobalt‐catalyzed [2+2+2] cycloaddition of a polyunsaturated compound displaying an ynamide, an alkyne, and a nitrile functionality (see picture).

     

Synthesis and Crystal Structure of Bis[2-[2-(diethylamino)ethyliminomethyl]-4-nitrophenolato]dimethanolcobalt(Ⅱ) Dinitrate

The title mononuclear cobalt(Ⅱ) complex [Co(DENP)2(MeOH)2]·2NO3 (DENP =2-[2-(diethylamino)ethyliminomethyl]-4-nitrophenolate) was prepared and characterized by elemental analysis, IR and single-crystal X-ray diffraction. The crystal belongs to the triclinic system, space group Pī with a = 8.297(1), b = 11.075(2), c = 11.134(2) (A), α = 69.69(1),β = 70.97(2), γ =84.02(2)°, Z = 1, V = 907.0(4) (A)3, Dc = 1.424 g/cm3, Mr = 777.66, λ(MoKα) = 0.71073 (A), μ = 0.548mm-1, F(000) = 409, R = 0.0628 and wR = 0.1734. The complex consists of a [Co(DENP)2-(MeOH)2]2+ cation and two disordered nitrate anions. The Co atom, lying at the inversion centre, is six-coordinated by two DENP ligands and two MeOH molecules in an octahedral geometry. The molecules in the crystal are linked through intermolecular O-H…O, O-H…N and N-H…O hydrogen bonds, forming chains parallel to the b axis.     

Synthesis and Crystal Structure of Bis[2-[2-(diethylamino)ethyliminomethyl]-4-nitrophenolato]dimethanolcobalt(II) Dinitrate

1 INTRODUCTION The significance of cobalt coordination com- pounds in biological systems is recognized[1～3]. In many instances the cobalt coordination compounds of Schiff bases have been suggested as models to describe energy transfer in naturally occurring systems. In such cases the coordination sphere about the metal ion is believed to play an important role in determining the nature of the model system[4, 5]. In order to investigate the structures of such complexes, we report herein t…     

Synthesis,reactions, and antimicrobial evaluations of new benzo[e][1,3]thiazine derivatives

4H-Spiro[benzo[d][1,3]oxathiine-2,1′-cyclohexan]-4-one undergoes aminolysis with certain aromatic amines to give the respective 4-benzenesulfonamide, Ethyl benzoate, and 4-acetylphenyl of 4-oxospirobenzo[e][1,3]thiazine derivatives. The Schiff bases prepared by reacting Ethyl benzoate derivative 2a with aldehydes, undergoes cyclocondensation with thioglycolic acid yielding p-methoxyphenyl and 2-(thiophen-2-yl) thiazolidinone derivatives. Treatment of the benzoate derivative with hydrazine hydrate afforded the corresponding benzohydrazide derivative which upon reaction with phenyl isocyanate and phenyl isothiocyanate afforded the urea and thiourea derivatives. New pyrimidine, pyridone, and imino pyridine derivatives of 4-oxospirobenzo[e][1,3]thiazine were also successfully prepared by reacting 2b or 2c with the appropriate organic reagents. Structural elucidations for the new products were based upon compatible microanalytical and spectroscopic measurements. Besides, their biological screening indicated that they possess potent antimicrobial activity in comparison with reference drugs.