Bicyclo octane structure

Thus, the predictions seem to be in conflict with the observed syn biases. However, along the trajectory of attack of the nucleophile to the carbonyl group of the bicyclo[2.2.2]octane structures (indicated in 23 and 24), out-of-phase interactions between the reagent and the substrate are involved, and this is different from the situation in the bicyclo[2.2.1]heptane structures (15a) [83-87]. Thus, attack on the side opposite to the unsaturated moiety will be favored. This is a kind of SOI (Fig. 3a) which unsymmetrizes the n face. 

A preliminary report of another Te82+ in a cage-like bicyclo[2.2.2]octane structure appeared in 1997.4 This structure is best understood as a Zintl structure in which the two bridgehead Te atoms bear the positive charge and three noncharged Te2 bridges are formed. However, no full structural report on this compound has been published and therefore we resist further analysis. 

While most tertiary amine catalysts are effective approximately in proportion to their base strength, an exception is triethylene diamine, 4-diaza[2.2.2]bicyclo-octane). As shown by Farkas et al. [142,143] this catalyst is much more powerful than would be predicted from its base strength, being five times stronger as a catalyst than iV,JV -dimethyl-piperazine, which has slightly greater basicity. It was first suggested that the explanation may be the complete lack of steric hindrance in the structure. 

However, if the norbornyl carbonium is brought to the proper temperature, passage to the more stable bicyclo[3.2.1]octane structure becomes possible. Lack of evidence for the reverse passage points to the lack of thermodynamic stability of the norbornyl structure even at low temperatures. 

The evolution of the systems with increasing temperature or reaction time indicates that bicyclo[3.2.1]octane structures, rather stable in the medium range of temperatures (160-200°) are irreversibly converted to bicyclo[3.3.0]octane isomers at higher temperatures (250°). They act as unstable intermediates whenever a temperature higher than 200° is required to pass from the bicyclo[2.2.1]heptane to the bicyclo[3.2.1]-octane, and this happens in the Gg and Cio series. 

The passage from bicyclo[2.2.2]octane structures to the isomeric bicyclo[3.2.1]octanes is irreversible for all practical purposes in the CsHiz and C9H14 series (it was not investigated in the CioHie series) and this conclusion is substantiated by other facts the acid-catalyzed dehydration of 2-methylbicyclo[3.2.1]-2-octanols and 3-methylbicyclo-[3.2.1]-3-octanols gives small quantities of methylbicyclo[2.2.2]octenes 30), while the acid-catalyzed hydration of bicyclo[2.2.2]-2-octene forms the bicyclo[3.2.1]-2-octanol 27) the nitrous acid deamination of 2-aminobicyclo[2.2.2]-5-octene goes to bicyclo[3.2.1]octenols 31) and the solvolysis of bicyclo[2.2.2]-5-octen-2-ol esters to bicyclo[3.2.1]octenols 32). 

The squalestatins, e.g. 6.28, also known as the zaragozic adds, have attracted considerable interest as inhibitors of squalene synthase and hence of cholesterol biosynthesis and lipid deposition in the circulatory system. They are also inhibitors of farnesyl protein transferase and thus they may have other potentially useful biological applications. They are formed by Phoma spedes and also by Setosphaeria khartoumensis. The squalestatins are characterized by a dioxabicyclo-octane core bearing three carboxyl groups and two polyketide chains, one of which is attached as an ester. The biosynthetic incorporation of succinic acid into part of the bicyclo-octane, together with its oxygenation pattern, indicate that it may be derived via oxaloacetic acid. Both the polyketide chains have several pendant methyl groups attached to them, which arise from methionine, whilst benzoic add ads as a starter unit for one of the chains. These complex structures are thus the summation of several biosynthetic pathways. 

Bases accelerate all the isocyanate reactions and in general their catalytic effect increases with increasing strength of the base. Table 4.7 compares the action of several amine catalysts at near ambient temperature. The significant increase in urethane reaction rate is apparent but particularly so in the case of triethylene diamine (l,4-diazo-[2,2,2]-bicyclo-octane), commonly known as DABCO. The reason for this is probably the complete lack of steric hindrance, given its cage-like structure. 

AAS = atomic absorption spectroscopy ATOF-MS = aerosol time-of-flight mass spectrometry 2,6-ndc = 2,6-naphthalenedicarboxylate bdc = 1,4-benzenedicar-boxylate bpdc = 1,3,5-benzenetricarboxylate bpydc = 2,2 -bipyridine-5,5 -dicarboxylate btb = 4,4, 4"-benzene-1,3,5-triylbenzoate btc = 1,3,5-benzenetricarboxylate 3D = three-dimensional dabco = l,4-diaza[2.2.2]bicyclo-octane EDX = energy-dispersive X-ray spectroscopy EXAFS = extended X-ray fine structure Fc = ferrocenyl ICP-AES = inductively coupled plasma atomic emission spectroscopy MOF = metal-organic framework PSD = postsynthetic deprotection PSM = Postsynthetic modification PXRD = Powder X-ray diffraction 1,4-ndc = 1,4-naphthalenedicarboxylate SALE = solvent-assisted linker exchange SBU = secondary building unit ... 

Optimize the structure of bicyclo[2.2.2]octane using three different optimization procedures ... 

The potential of Fischer carbene complexes in the construction of complex structures from simple starting materials is nicely reflected in the next example. Thus, the reaction of alkenylcarbene complexes of chromium and tungsten with cyclopentanone and cyclohexanone enamines allows the di-astereo- and enantioselective synthesis of functionalised bicyclo[3.2.1]octane and bicyclo[3.3.1]nonane derivatives [12] (Scheme 44). The mechanism of this transformation is initiated by a 1,4-addition of the C -enamine to the alkenylcarbene complex. Further 1,2-addition of the of the newly formed enamine to the carbene carbon leads to a metalate intermediate which can... 

Fig. 5 (a) Structure directing agent (SDA) in the synthesis of zeolite ITQ-3 N quaternary nitrogen A-I carbon atoms of SDA, l,3,3,6,6-pentamethyl-6-azonium-bicyclo[3.2.1]octane some 13C line assignments were not unequivocally possible, so these are left open the orientation of the dipole moment was calculated with a semiempirical AM-1 simulation with the origin at the center of gravity of the molecular cation (b) 13C H 27A1 REAPDOR experiment on synthetic zeolite ITQ-3. Adapted from [204]... 

Theoretical calculation at the HF/6-31G level99,102 on some S-S dications and their precursors have shown that the electronic structure of 1,4-dithionia-bicyclo[2.2.0]hexane and the sp-sp conformation of the tetramethyldisulfonium dication, the difference in the energy levels of [S] — [S] and [S] + n[S]103 is decreased owing to steric strain and the order of orbitals thus corresponds to case B. In the less strained systems (l,5-dithioniabicyclo[3.3.0]octane, 1,4-dithioniabicyclo[3.2.0]heptane), the order of orbitals corresponds to case C. Interestingly, ap-ap conformer of tetramethyldisulfonium dication was reported to correspond to case A. 

The structures of [2]ladderane and [3]ladderane were determined by electron diffraction.22,23 Each cyclobutane ring of bicyclo[2.2.0]hexane has a folded structure with fold angle 11.5°, and the molecule has C2 symmetry.22 Anti- and yy/7-tricyclo[4.2.0.02,5]octanes also have folded cyclobutane rings with fold angles of 8.0 and 9.0°, respectively.23 MM2 calculations on... 

The cyclohexasilane ring of trans-lfl has a chair form and both chlorine atoms occupy axial positions. The cyclotetrasilane ring has a folded structure with the fold angles of 33.0 and 33.6°. The structure of the silicon framework of trans-lfl resembles that of bicyclo[4.2.0]octane, in which the cyclohexane ring has a chair form and the cyclobutane ring has a folded structure.67... 

Figure 6. Structural formulae of S-D amphiphilic compounds and other chemicals used for S-D monolayers for comparison of photo-induced electron transfer rates between a single alkyl chain and a triple alkyl chain as the spacers of the S-D dyads with the same length of four-carbons. In these S-D dyads, a naphthalene and a ferrocene moiety are used as an S and a D moiety, respectively. S-D dyads with a rigid spacer consisting of a bicyclo[2.2.2]octane are used as dyads with a triple alkyl chain.

The results obtained in combination with the data on the transformations of cations 9-11, led to the conclusion that 1,2-shifts of methyl groups occur readily in carbocations having a pentalene fragment. On the basis of the data obtained for rearrangements of such carbocations, an alternative mechanism has been proposed (52) for the rearrangement of structurally related carbocation 16 having a bicyclo[3.3.0]octane skeleton described in (33) (Scheme 12). 

Both the cis and trans isomers of bicyclo[4.2.0] octane are other examples of the auxiliary use of the MM method in precise structure determinations by vapor phase electron diffraction (115a). 

The X-ray crystal structure of the hexafluoroantimonate salt of 1,4-diithin radical cation stabilized by bicyclo[2.2.2]octane annelation revealed a planar ring and was in agreement with theoretical calculations. Tertiary aminium radical cations underwent facile 5-exo-cyclization to give distonic 2-substituted pyrrolidinium radical cations. 

The Cj - and 54-symmetric tetraesters of tricyclo[3.3.0.0 ]octane (430 and 431) have been prepared by oxidation of diene 429 To access the parent hydrocarbon (435), acid chloride 432 was transformed to the derived ketene which undergoes intramolecular [2+2] cycloaddition The resulting cyclobutanone (433) serves as precursor to perester 434 whose thermal decomposition proceeds with chain transfer in competition with cleavage The unique arrangement of the carbon atoms in 435 is such that the smallest rings are all five-membered. The highly symmetric structure may be viewed as a constrained cisoid bicyclo[3.3.0]octane (as well as the symbol of NATO). 

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