Preparation and Diels-Alder Reactivity of Tricarbonyliron Complexes of [2.2.2]Hericene

Treatment of [2.2.2]hericene 10 with Fe₂(CO)₉ in hexane gave a mixture of monometallic complex 14 , two isomeric dimetallic complexes 15 and 16 , and a trimetallic complex 19 in which all the three diene moieties of 10 , are coordinated. The rate constants of the Diels-Alder additions of tetracyanoethylene (TCE) and dimethyl acetylenedicarboxylate (DMAD) to the uncomplexed diene moieties of 14–16 have been evaluated and compared with those measured for the uncomplexed 10 and its monoadducts 11A, 11B and bis-adducts 12A, 12B. The tricarbonyldieneiron function retards the cycloaddition of an homoconjugated, exocyclic s-cis-butadiene. The effect is significantly larger for TCE- than for DMAD-additions. The origin of this effect is discussed briefly in terms of the valence-bond model which is usually assumed to describe the properties of a tricarbonyldieneiron complex, and in terms of the inductive and steric factors of the Fe(CO)₃-group.     

Face Selectivity of the Diels-Alder Reaction of 5,6-Bis((D)methylidene)-2-bicyclo[2.2.2]octene

The face selectivity (endo-face vs. exo-face attack onto the exocyclic s-cis-butadiene moiety) of the [4+2]cycloadditions of 5,6-bis((D)methylidene)-2-bicyclo-[2.2.2]octene ( 11 ) to strong dienophiles has been determined in benzene at 25°. It is ca. 95/5, 75/5, 70/30, 60/40 and 50/50 for N-phenyltriazolinedione (NPTAD), tetracyanoethylene (TCE), dimethyl acetylenedicarboxylate (DMAD), maleic anhydride (MA) and singlet oxygen (¹O₂), respectively. The endo-face preference is probably due to a participation of the homoconjugated double bond at C(2), C(3) which makes the etheno bridge more polarizable than the ethano bridge in 11. The absence of face selectivity with ¹O₂ is consistent with an entropy-controlled mechanism involving the intermediacy of an exciplex.     

Nature of the 2-bicyclo[3.2.1]octanyl and 2-bicyclo[3.2.2]nonanyl cations.

Density functional and ab initio calculations have been employed to explore the nature of the cations formed in the solvolysis of 2-bicyclo[3.2.1]octanyl tosylate the 2-bicyclo[3.2.2]nonanyl tosylate. In contrast to recent conclusions in the literature, the various proposed classical carbocations postulated to explain the products of the 2-bicyclo[3.2.2]nonanyl tosylate solvolysis were found to have nonclassical structures.     

Charge-transfer bands of bicyclic β,γ-unsaturated ketones. Circular dichroism of (+)-(1R)-5,6-dimethylidene-2-bicyclo[2.2.2]octanone and (+)-(1R)-2-bicyclo[2.2.2]oct-5-enone

An “extra” band between those attributed to the carbonyl and olefinic chromophores has been found in the CD spectra of bicyclic ketones homoconjugated to endocyclic olefins or exocyolic dienes.     

Iron and molybdenum carbonyls of 5,6,7,8-tetramethylenebicyclo[2.2.2]-oct-2-ene

The reaction of the title ligand with iron carbonyls under various conditions gives (tetrahapto)5,6,7,8-tetramethylenebicyclo[2.2.2]oct-2-ene-exotricarbonyliron (I) and the bis(tetrahapto)endoexo-(II) and diexohexacarbonyl diiron (III) complexes as main products. The monoexo complex reacts with Mo(CO)₃(CH₃CN)₃ giving a (tetrahapto)iron(hexahapto)molybdenum complex (IV).     

Synthesis and Reactivity of Bis(silylene)-Coordinated Calcium and Divalent Lanthanide Complexes

Divalent lanthanide complexes of Eu ( 1 ) and Yb ( 2 ) coordinated by a chelating pyridine-based bis(silylene) ligand were isolated and fully characterized. Compared to the Eu^II complex 1 , the Yb^II complex 2 presents a lower thermal stability, resulting in the activation of one Si^II−N bond and formation of an Yb^III complex ( 3 ), which features a unique silylene-pyridyl-amido ligand. The different thermal stability of 1 and 2 points towards reduction-induced cleavage of one Si^II−N bond of the bis(silylene) ligand. Successful isolation of the corresponding redox-inert bis(silylene) Ca^II complex ( 5 ) was achieved at low temperature and thermal decomposition into a Ca^II complex ( 4 ) bearing the same silylene-pyridyl-amido ligand was identified. In this case, the thermolysis reaction proceeds through another, non-redox induced, mechanism. An alternative higher yielding route to 4 was developed through an in situ generated silylene-pyridyl-amine proligand.     

Selective Formation and Unusual Reactivity of Tetraarsabicyclo[1.1.0]butane Complexes

The selective formation of the dinuclear butterfly complexes [{Cp′′′Fe(CO)₂}₂(μ,η^1:1‐E₄)] (E=P ( 1 a ), As ( 1 b )) and [{Cp*Cr(CO)₃}₂(μ,η^1:1‐E₄)] (E=P ( 2 a ), As ( 2 b )) as new representatives of this rare class of compounds was found by reaction of E₄ with the corresponding dimeric carbonyl complexes. Complexes 1 b and 2 b are the first As₄ butterfly compounds with a bridging coordination mode. Moreover, first studies regarding the reactivity of 1 b and 2 b are presented, revealing the formation of the unprecedented As₈ cuneane complexes [{Cp′′′Fe(CO)₂}₂{Cp′′′Fe(CO)}₂(μ₄,η^1:1:2:2‐As₈)] ( 3 b ) and [{Cp*Cr(CO)₃}₄(μ₄,η^1:1:1:1‐As₈)] ( 4 ). The compounds are fully characterized by NMR and IR spectroscopy as well as by X‐ray structure analysis. In addition, DFT calculations give insight into the transformation pathway from the E₄ butterfly to the corresponding cuneane structural motif.     

Interaction between Exocyclic s-cis-Butadiene and Homoconjugated Functions. Preparation and Diels-Alder Reactivity of Remotely Substituted 2,3-Dimethylidenebicyclo[2.2.2]octanes

The preparations of 5,6-dimethylidene-2exo-bicyclo[2.2.2]octanol ( 8 ), its endo isomer 9 , 5,6-dimethylidene-2-bicyclo[2.2.2]octanone ( 10 ) and 2 exo, 3 exo-epoxy-5,6dimethylidenebicyclo[2.2.2]octane ( 11 ) are described. The kinetics of their cycloaddition to tetracyanoethylene has been measured in toluene at 25° together with those of 2,3-dimethylidenebicyclo[2.2.2]octane ( 7 ) and 5,6-dimethylidenebicyclo[2.2.2]oct-2-ene (12). The effects of remote substitution on the Diels-Alder reactivity of 2,3-dimethyl idenebicyclo[2.2.2]octanes are compared with those observed in the 2,3-dimethylidenenorbornane series ( 1–6 ).     

The Photochemistry of 5,6-Dimethylidene-2-norborananone. Synthesis and Diels-Alder Reactivity of 2,3-Dimethylidenebicyclo-[2.1.1]hexane

2,3-Dimethylidenebicyclo [2.1.1]hexane (4) was isolated from direct irradiation (253.7 nm) of 5,6-dimethylidene-2-norbornanone (3) . Quenching experiments at 253.7 nm, as well as direct and sensitized irradiations at >300 nm suggested that a high vibrationally excited S₁- or a S₂-state is required for the photodecarbonylation of 3 in contrast with other β, γ-unsaturated ketones for which α-cleavage occurs with lower excitation-energy. The new diene 4 reacted toward tetracyano-ethylene (k (1mol^?1 s^?1))=(3.1±0.34) · 10^?3) in toluene and (6.2±0.11) · 10^?3 in benzene only 60 times more slowly than 2,3-dimethylidenenorbornane (5) and ca. 850 times as fast as 2,3-dimethylidene-syn1,4,5,6-tetramethylbicyclo[2.1.1]-hexane (9) .     

Reactivity with Amines of Bis(cyanamide) and Bis(cyanoguanidine) Complexes of the Iron Triad

Treatment of bis(cyanamide) [M(N≡CNEt₂)₂L₄](BPh₄)₂ and bis(cyanoguanidine) [M{N≡CN(H)C(NH₂)=NH}₂L₄](BPh₄)₂ complexes [M = Fe, Ru, Os; L = P(OEt)₃] with an excess of amine RNH₂ (R = nPr, iPr) affords mixed‐ligand complexes with cyanamide and amine [M(NH₂R)(N≡CNEt₂)L₄](BPh₄)₂ ( 1a – 5a ) and [M(NH₂R){N≡CN(H)C(NH₂)=NH}L₄](BPh₄)₂ ( 1b , 2b ). The complexes were characterized by spectroscopy and X‐ray crystal structure determination of [M(NH₂iPr)(N≡CNEt₂){P(OEt)₃}₄](BPh₄)₂ [M = Ru ( 3a ), Os ( 5a )].     

Asymmetric Diels—Alder Reaction Catalyzed by Novel Chiral Dibenzo[a,c] cycloheptadiene Bis（oxazoline） Metal Complexes

A series of novel chiral C2-symmetric bis (oxazoline) ligands have been synthesized.The copper and magnesium complexes,prepared in situ from copper(Ⅱ)-triflate of magnesium triflate with the new enantiopure oxazoline ligands,were evaluated as chiral catalysts in the enantioselective Diels-Alder reaction of cyclopentadiene with N-crotenoyl-oxazolidin-2-one.Primary results showed that diastereoselectivity up to 94% and enantioselectivity up to 68% ee for endo products were observed respectively with these ligands.     

Domino retro Diels-Alder/Diels-Alder reaction: an efficient protocol for the synthesis of highly functionalized bicyclo[2.2.2]octenones and bicyclo[2.2.2]octadienones

A novel and convenient approach, the domino retro Diels-Alder/Diels-Alder reaction sequence for highly stereo- and regioselective synthesis of various bicyclo[2.2.2]octenone and bicyclo[2.2.2]octadienone derivatives is presented. Thus, the masked o-benzoquinones (MOBs) 2a-e generated by the pyrolysis of the respective dimers 3a-e participated in this novel synthetic strategy with a variety of olefinic and acetylenic dienophiles at 220 degrees C to provide the title compounds in good to excellent yields.     

选择性合成双[噻吩并[2,3-d]嘧啶-4(3H)-酮]

以2-氨基-4-三氟甲基-5-甲基-噻吩-3-羧酸乙酯(1)为起始原料制得膦亚胺2.在碳酸钾的催化下,膦亚胺2与芳基异氰酸酯和伯二胺的氮杂Wittig反应制得嘧啶环上2,2’取代的双[噻吩并[2,3-d]嘧啶-4(3H)-酮]3;膦亚胺2与烷基异氰酸酯和伯二胺的氮杂Wittig反应制得嘧啶环上3,3’取代的双[噻吩并[2,3-d]嘧啶-4(3H)-酮]4.化合物3的核磁共振氢谱表明关环反应在嘧啶环的2,2’位;化合物4的核磁共振氢谱表明关环反应在嘧啶环的3,3’位.对合成反应机理的推导及目标产物核磁共振氢谱数据的分析解释了此合成反应的选择性.     

Preparation and Spectral Investigation of Bis[N(2-methyl-phenyl) 4-Nitro-thiobenzamidato] mercury(II), Bis[N(2-methoxy-phenyl) 4-Nitro-thiobenzamidato]mercury(II), and Bis[N(2-chloro-phenyl) 4-Nitro-thiobenzamidato]mercury(II) Complexes

Several preparative routes to bis[N(substituted-phenyl) 4-nitro-thiobenzamidato] mercury(II) complexes are presented, including the reaction of mercury(II) oxide, fluoride, chloride, bromide, cyanide, acetate, and nitrate with N(substituted-phenyl) 4-nitro-thiobenzamide derivatives. ¹ H-NMR, Raman, and IR measurements confirmed the complexation of mercury to sulphur.     

Bis(dibenzo[c.e][1,2]oxaphosphorino)dichloroplatinum Complexes

Reaction of a series of P-amino and P-cycloalkoxy dibenzo[c.e][1,2]oxaphosphorines (1), (3) and (5) with cis-bis(benzonitrile)dichloroplatinum(II) afforded the title bis(dibenzooxaphosphorino) complexes (2), (4) and (6), respectively. In the case of chiral P-substituents, the complexes (4) and (6) were obtained in homo and heterochiral forms. Stereospecific ¹J(¹⁹⁵Pt–P) couplings found in the ³¹P-n.m.r. spectra of the products (2), (4) and (6) suggested the cis orientation of the identical substituents.     

Regioselectivity of the Diels-Alder Additions of 2-Substituted 5,6 Dimethylidenenorbornanes and-bicyclo[2.2.2]octanes

The cycloadditions of methyl propynoate and methyl vinyl ketone to 5,6-dimethylidene-2-norbornanone ( 6 ) are para′-regioselective

1 “Para” (p) designs in this paper the 4, 9-disubstituted tricclo[6.2.1.0^{2, 7}] undecane- and 4, 9-disubsstituted tricycle[6.2.20^2,7] dodecane derivatives, “meta” (m) design the corresponding 4, 10-disubstituted compounds.

. A smaller para -regioselectivity is observed for the addition of methyl propynoate to 5,6-dimethylidene-2bicyclo[2.2.2]octanone ( 10 ). No regioselectivity is observed with 5,6-dimethylidene-2exo-norbornyl alcohol ( 3 ), acetate ( 5 ) and 5,6-dimethylidene-2exo-bicyclo[2.2.2]octanol ( 9 ). PMO arguments based on the shape of the HOMO's and subHOMO's of the dienes allow to rationalize these observations. Unpredictable para′- or ‘meta’regioselectivities are found for the Diels,-Alder additions of 5,6-dimethylidene-2endo-norbornyl alcohol ( 2 ), acetate ( 4 ) and 5,6-dimethylidene-2endo-bicyclo[2.2.2]octanol ( 8 ). The carbonyl group of β,γ unsaturated ketones such as 6 and 10 can act as an electron donating homoconjugated substituent. The n(CO) ? σ[C(1), C(2)] ? π[C(5), C(6)] hyperconjugative interaction can override the usual electron-withdrawing effect of this function.