Face Selectivity of the Diels-Alder Reaction of Hexadienone Moieties Grafted onto the Bicyclo[2.2.2]octene Skeleton and Perturbed by a Remote Tricarbonylbutadieneiron Group

Selective oxidations of bis(tricarbonyliron) complexes of methyl (3,7,8-trimethylidenebicyclo[2.2.2]oct-5-en-2-ylidene)methyl ketones 15 – 17 afforded selectively the tricarbonyl {(1RS,4SR,7SR,8RS)-C,7,8,C-η-[methyl (3,7,8-trimethylidenebicyclo[2.2.2]oct-5-en-(2Z)-2-ylidene)methyl ketone]}iron ( 12 ), the corresponding (2E)-derivative 13 and the tricarbonyl{(1RS,2RS,3SR,4SR)-C,2,3,C-η-[methyl (3,7,8-trimethylidenebicyclo[2.2.2]oct-5-en-(2Z)-2-ylidene)methyl ketone]}iron ( 18 ). The stereoselectivity of the Diels-Alder reactions of the uncomplexed (Z)- and (E)-hexadienone 12 and 13 , respectively, was established. The face of the diene syn with respect to the C(5), C(6) etheno bridge was preferred for the cycloadditions of N-phenyltriazolinedione (NPTAD). In contrast, the reactions of dimethyl acetylenedicarboxylate (DMAD) and methyl propynoate showed a slight preference for addtion to the face of the hexadienones anti with respect to the etheno bridges of 12 and 13 . The crystal structure of the adduct 25 resulting from the cycloaddition of NPTAD to 12 is reported.     

Stereoselectivity of the Diels-Alder additions of exocyclic dienes grafted onto bicyclo[2.2.n]alkanes

The stereoselectivity of the Diels-Alder additions of (norborn-2-eno) [c]furan, (E,E)-5,6-bis(chloromethylene)bicyclo[2.2.2]oct-2-ene, (E,E)-5,6-bis(chloromethylene)-exo-2,3-epoxybicyclo[2.2.2]octane, (E)- and (Z)-2-chloromethylene-3-methylene-exo-5,6-bis(chloromethyl)-7-oxanorbornanes is presented.     

Mass spectral study of bicyclic peroxides. 1. Dioxabicyclo[n.2.2]alkanes and the corresponding dioxabicyclo[n.2.2]alkenes

A series of dioxabicyclo[n.2.2]alkanes (n = 1,2,3 and 4) and dioxabicyclo[n.2.2]alkenes were studied under electron impact ionization. The fragmentation pathways were elucidated with the aid of accurate mass measurements, metastable scan techniojei and deuterium labelling. The preferential fragmentation of molecular ions in dioxabicyclo[n.2.2]alkanes corresponds to the loss of hydroperoxyl radical ·OOH. Hydrogens that are participating in this elimination come primarily from the syn position on the two-membered carbon bridge. The dioxabicyclo[n.2.2]alkenes undergo the retro-Diels–Alder process, which produces dioxygen and 1,3-cycloalkadiene. In both saturated and unsatutated peroxides subsequent fragmentation of the hydrocarbon ring depends upon the value of n.     

Conformational analysis of 2,3,5,6-tetrakis(methylene)bicyclo[2.2.2]octanes by circular dichroism.

The variable temperature CD spectra of (+)-(7R)-7-deuterio- and (+)-(7S)-7-methyl-2,3,5,6-tetrakis(methylene)bicyclo[2.2.2]octane suggest single energy minimum hypersurfaces with eclipsed bicyclic skeletons and planar dienes whereas that of (?)-(2R)-5,6,7,8-tetrakis-(methylene)-2-bicyclo(2.2.2]octanol is consistent with a twisted structure.     

Effects of Remote Substitution on the Photo-oxidation of Exocyclic s-cis-Butadienes Grafted onto Bicyclo [2.2.1]heptanes. Thermal and Rhodium Catalyzed Rearrangements of 3,6-Dihydro-1,2-dioxines

The rates of photo-oxidation of exocyclic S-cis-butadienes grafted onto bicyclo-[2.2.1]heptanes and 7-oxabicyclo[2.2.1]heptanes ( 1–6 ) are dependent upon remote modifications of the bicyclic skeletons. They correlate with the rates of Diels-Alder additions of these dienes to strong dienophiles. The 2,3-dimethylidenenorbornane ( 1 ), 5,6-dimethylidene-2-norbornene ( 2 ) and 2,3-dimethylidene-7-oxanorbornane ( 3 ) gave the corresponding endo-peroxides (3,6-dihydro-1,2-dioxines) 7–9 in good yield. The 2, 3, 5, 6-tetramethylidene-7-oxanorbornane ( 4 ) gave the mono-endo-pe-roxide 6 , the latter did not react with a second equivalent of oxygen. Similarly, 5, 6-dimethylidene-7-oxa-2-norbornene ( 5 ) was unreactive toward photo-oxidation. Thermal isomerization of the endo-peroxides 7 and 9 gave, the trans-diepoxides 10 and 14 , respectively, with high stereoselectivity. The endo-peroxides 6 , 7 and 9 were cleanly isomerized into the corresponding α, β-unsaturated γ-hydroxy aldehydes in the presence of catalytic amounts of Rh₂(CO)₄Cl₂.     

Stereoselectivity in the Diels‐Alder Cycloadditions of a Facially Dissymmetric Bicyclo[2.2.2]octadiene‐Grafted Maleic Anhydride with Exocyclic Butadienes. Unexpected Facial Selectivity in the Cycloaddition with 2,3,5,6‐tetramethylidenebicyclo[2.2.2]octene

The Diels‐Alder cycloadditions of facially dissymmetric maleic anhydride 1 with facially nonequivalent exocyclic 1,3‐butadienes(dimethylidenebicyclo[2.2.2]octene 3 and 2,3,5,6‐tetramethylidenebicyclo[2.2.2]‐octene ( 4 )) were investigated. In each cycloaddition, the reaction occurred via the course in which 1 added exclusively by its syn‐face (same face as the etheno‐bridge) onto either π‐face of the exocyclic 1,3‐butadiene systems to produce only two of the four possible stereoisomeric monocycloadducts ( 8a / 8b and 9a / 9b ). In the Diels‐Alder cycloaddition of 1 with bis‐exocyclic butadiene 4 , however, both monocycloadducts 9a and 9b underwent subsequent cycloaddition with distinctive facial selectivity to produce the C_s‐symmetric bis‐cyclohexanobarrelene 10a as only bis‐cycloadduct.     

双环[2.2.2]辛-7-烯-2，3，5，6-四羧酸铜配合物的合成和晶体结构研究

以双环[2.2.2]辛-7-烯-2,3,5,6-四羧酸(H4L)为配体,采用水热法合成了个铜配合物[Cu2L2(H2O)2](2),并得到单晶,同时在水热条件下得到了化合物H4L.2H2O(1)的晶体。分别对化合物1和2进行了元素分析、红外光谱等分析,并用X-射线单晶衍射测定了化合物的单晶结构。化合物1属于三斜晶系,P1空间群,化合物1的晶体学数据为:a=0.88554(15)nm,b=0.95566(16)nm,c=1.043 88(17)nm,α=110.863(3)°,β=91.127(3)°,γ=91.429(3)°,V=0.824 9(2)nm3,Z=2,Mr=366.32,Dc=1.475 g.cm-3,F(000)=388,μ=0.129,R1=0.067 0,wR2=0.189 3;配合物2属于正交晶系,Pnnm空间群,配合物2的晶体学数据为:a=2.766 8(6)nm,b=0.638 75(14)nm,c=0.737 32(16)nm,V=1.303 1(5)nm3,Z=4,Mr=442.31,Dc=2.254 g.cm-3,F(000)=884,μ=3.324,R1=0.059 4和wR2=0.191 7。化合物1通过氢键形成三维网状结构,配合物2中的中心离子有3种配位方式,通过不同的配位方式也形成三维结构。     

Regioselective Electrophilic Additions of Bicyclo[2.2.n]alk-2-enes Controlled by Remote Epoxide Functions

The electrophilic additions of 2-nitrobenzenesulfenyl chloride to (1RS,2SR,4RS)-spiro[bicyclo[2.2.1]hept-5-ene-2,2′-oxirane] ( 12 ) and (1RS,2SR,4RS)-spiro[bicyclo[2.2.2]oct-5-ene-2,2′-oxirane] ( 14 ) were not regioselective under condition of kinetic control. However, good regioselectivity was observed for the addition of 2-nitro-benzenesulfenyl chloride to (1RS,2RS,4RS)-spiro[bicyclo[2.2.1]hept-5-ene-2,2′-oxirane] ( 13 ), giving (1RS,2SR,4SR,5RS,6RS)-6-exo-(2-nitrophenylthio)spiro[bicyclo[2.2.1]heptane-2.2′-oxirane]-5-endo-yl chloride ( 24 ) and for the exo addition to (1RS,2RS.4RS)-spiro[bicyclo[2.2.2]oct05-ene-2,2′-oxirane] ( 15 ), giving preferntially (1RS,2SR,4SR,5RS,6 RS)-6-exo-(2-nitrophenylthio) spiro[bicyxlo[2.2.2]octane-2,2′-oxirane]-5-endo-yl chloride ( 30 ). The facial selectivity (electrophilic exo vs. endo attack on the bucyclic alkene) depended on the relative configuration of the spiroepoxide ring in the bicyclo[2.2.2]octenes 14 and 15 . The exo-epoxide 14 was attacked preferentially (6:1) on the endo face by sulfenyl whereas exo attack was preferred (7:2) in the case of the endo-epoxide 15 . No products resulting from transannular ring expansion of the spiro-epoxide moieties could be detected.     

The Non-planarity of the Bicyclo[2.2.1]hept-2-ene Double bond. Crystal Structures of Bicyclo[2.2.2]oct-2-ene,Bicyclo[2.2.1]hept-2-ene,and Bicyclo[2.1.1]hex-2-ene Systems

The crystal structures of (1R,4R,5S,8S)-9,10-dimethylidentricyclo[6.2.1.0^2,7]undec2(7)-ene-4,5-dicarboxylic anhydride ( 3 ), (1R,4R,5S,8S)11-isopropylidene-9,10-dimethylidenetricyclo[6.2.1.m^2,7]undec-2(7)-ene-4,5-dicarboxylic anhydride ( 6 ), (1R,4R,5S8S)-9,10-dimethylidenetricyclo[6.2.2.0^2,7]dodec-2(7)-ene-4,5-dicarboxylic anhydride ( 9 ), (1R4R5S8S)-TRICYCLO[6.2.2.0^2,7]dodeca-2(7), 9-diene-4,5-dicarboxylic anhydride ( 12 ) and (4R,5S)-tricyclo[6.1.1.0^2.7]dec-2(7)-ene-4,5-dicarboxylic acid ( 16 ) were established by X-ray diffraction. The alkyl substituents onto the endocyclic bicyclo[2.2.1]hept-2-ene double bond deviate from the C(1), C(2), C(3), C(4), plane by 13.5°4 in 3 and by 13.9° in 6 , leaning toward the endo-face. No such out-of-plane deformations were observed with the bicyclo[2.2.2]oct-2-ene derivatives 9 and 12 . The exocyclic s-cis-butadiene moieties in 3, 6 and 9 do not deviate significantly from planarity. The deviation from planarity of the double bond n bicyclo[2.2.1]hept-2-ene derivatives and planarity in bicyclo[2.2.2]oct-2-ene analogues is shown to be general by analysis of all known structures in the Cambridge Crystallographic Data File. The non-planarity of the bicyclo[2.2.1]hept-2-ene double bond cannot be attributed only to bond-angle deformations which would favour rehybridizatoin of the olefinic C-atoms since the double bond in the more strained bicyclo[2.1.1]hex-2-ene drivative 16 deviates from planarity by less than 4°.     

Neighboring Group Participation in a Regio- and Stereoselective Chlorination of a Bicyclo[2.2.2]octanone

The zinc chloride-mediated acetylation of the optically active silyl enol ether 2a gave the beta-diketone 3a (48%) together with the regio- and stereoselectively chlorinated compound 4 (27%). The yield of 4 increased to 70% by starting from the O-acetyl derivative 2c. The chlorination most likely occurs via neighboring group participation by the endo acetoxy group.     

Polar Effects in the Solvolysis of 4-Substituted Bicyclo [2.2.2]octyl p-Nitrobenzenesulfonates. Polar effects. VII

Hydrolysis of bicyclo[2.2.2]octylp-nitrobenzenesulfonate ( 14a , X = p-NO₂C₆H₄SO₃), and nineteen 4-R-substituted derivatives 14b–14t in 70% aqueous dioxane yield the corresponding bicyclo[2.2.2]octanols 14 (X = OH), exclusively. The 7-center fragmentation to 1,4-dimethylidene-cyclohexane ( 15 ) is not observed. The logarithms of most of the rate constants, measured in 80% ethanol, correlate well with the corresponding inductive substituent constants σ of R. Hence, in these cases ionization rate is controlled by the inductive effect of R only. Poor correlations result when the substituents are potentially electrofugal groups, such as COO^?, CH₂OH, CH₂NH₂, CONH₂ and H, the deviations from the inductive regression line corresponding to rate enhancements of 1.6 to 8. These exalted substituent effects are tentatively ascribed to extended hyperconjugation involving two σ-bonds. This study corroborates previous evidence that the inductive effect alone does not fully account for the polar effect of some substituents in reactions involving carbocations.     

Conformation of bicyclo[n.1.0]-compounds: Part I. Bicyclo[5.1.0] octane and cycloheptene epoxide

MINDO/3 quantum-mechanical calculations indicate that the most stable conformations of cis-bicyclo[5.1.0]octane and cycloheptene epoxide are the chair—chair (CC) and boat—chair (BC) conformations, respectively. The possible pathways of interconversion have been studied and are discussed for each molecule. The geometry of trans-bicyclo[5.1.0]-octane has been calculated and a heat of isomerization of 3.8 kcal mol^?1 has been obtained. Theoretical results are compared with the experimental data available.     

Thermotropic Copolyesters. 1. Synthesis and Characterization of Liquid Crystal Copolyesters Containing the Bicyclo [2.2.2]octane Ring System

The syntheses and characterizations of poiy[oxy(2-chloro-l,4-phenylene)oxycarbonyl- l,4-bicyclo[2.2.2] octylenecarbonyl-co-oxy(2-chloro-l,4-phenylene)oxysebacoyl] and poly[oxy(2-methyl-l,4-phenylene)oxycarbonyl-l,4-bicyclo[2.2.2]octylenecarbonyl-co-oxy(2-methyl-l,4-phenylene)oxysebacoyl] are described. The resulting random copolyesters were characterized by infrared spectroscopy, proton magnetic resonance spectroscopy, solution viscosity, and differential scanning calorimetry. The random copolyesters formed birefringent fluid states in the melt.     

Structure of Tricarbonyl(diene)iron Complexes in Solution. Variable-Temperature Circular Dichroism of trans-μ-(2,3,5,6-Tetramethylidenebicyclo[2.2.2]octane)bis(tricarbonyliron) Complexes

Optically pure (?)-trans-μ-[(1R,2R,3S,4S,5S,6R)-C,2,3,C-η:C,5,6,C-η-(2,3,5,6,7-pentamethylidenebicyclo[2.2.2]octane)]bis(tricarbonyliron) ((?)- 9 ), (?)-trans-μ-[(1R,2R,3S,4S,5S,6R,7S)-C,2,3,C-η:C,5,6,C-η-(7-methyl-2,3,5,6-tetramethylidenebicyclo[2.2.2]octane)]bis(tricarbonyliron) ((?)- 10 ), and (?)-trans-μ-[(1R,2R,3S,4S,5S,6R,7R)-C,2,3,C-η:C,5,6,C-η-(2,3,5,6-tetramethylidene(7D)bicyclo[2.2.2]octane)]bis(tricarbonyliron) ((?)- 16 ) have been prepared. Their CD spectra were solvent- and concentration-independent, but temperature-dependent, in accord with the existence of equilibria between rapidly interconverting diastereoisomeric species which can be interpreted as arising from distortions of the tricarbonyl(diene)iron units from the C_s symmetry.     

Conformational analysis of bridgehead-substituted bicyclo[m.m.m]alkanes and bicyclo[8.8.n]alkanes

Conformational analyses of bicyclo[m.m.m]alkanes where m=1-10 and of bicyclo[8.8.n]alkanes where n=1-7 bearing methyl groups on the bridgeheads were carried out using a Monte Carlo search strategy. In the bicyclo[m.m.m]alkane series, greater variability was observed for the inter-bridgehead distance for larger values of m. This suggests that properly substituted bicyclo[8.8.8]hexacosanes or larger ring systems might serve as molecular springs.     

Synthesis of Bicyclo[n.1.0]alkanes by a Cobalt‐Catalyzed Multiple C(sp3)−H Activation Strategy

A cobalt‐catalyzed dual C(sp³)−H activation strategy has been developed and it provides a novel strategy for the synthesis of bicyclo[4.1.0]heptanes and bicyclo[3.1.0]hexanes. A key to the success of this reaction is the conformation‐induced methylene C(sp³)−H activation of the resulting cobaltabicyclo[4.n.1] intermediate. In addition, the synthesis of bicyclo[3.1.0]hexane from pivalamide, by a triple C(sp³)−H activation, has also been demonstrated.