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Bicyclo butan

Bicyclo[2.1.0]pentane (62) reacts thermally (120°C, 48 h), with electron-poor olefins via a stepwise, diradical mechanism to afford bicyclo[2.2.1]heptane products derived from the addition of the olefins on the endo side of the bicyclo envelope . On the other hand in the presence of nickel(O) catalysts, the addition occurs under milder reaction conditions and with an alternative stereochemistry, i.e. predominantly on the exo face (equation 42) No class of transition metal catalysed rearrangements has been the subject of more controversy than those of bicyclo butane. A general mechanistic picture, consistent with the experimental facts, has, however, been presented ... [Pg.823]

Like protons, transition-metal ions are strongly acidic and they can, in principle, add to both the C—H and C—C bonds of alkanes. As already noted in the section on proton affinities (Table 1) strained cycloalkanes are intrinsically more basic than open-chain alkanes, and the reaction of cyclopropane with Pt((II) to form a platinacyclo-butane (equation 14) was the first reaction of a formally saturated hydrocarbon with a transition-metal ion . The driving force in this reaction is relief of the strain associated with the small ring. The resulting metallacyclobutane is essentially free of ring strain. Many low-valent transition-metal complexes have been found to react with cycloalkanes. Metal ions convet the strained hydrocarbons quadricyclane , cubane , bicyclo-[2.1.0]pentanes , bicyclo[3.1.0]hexanes , bicyclo[4.1.0]heptanes and bicyclo-butanes into less strained isomers (usually cyclohexanes). [Pg.540]

The decalin (bicyclo[4.4.0]decane) ring system provides another important system for study of conformational effects in cyclohexane rings. Equilibration of the cis and trans isomers reveals that the trans isomer is favored by about 2.8 kcal/mol. Note that this represents a change in configuration, not conformation. The energy difference can be analyzed by noting that the cis isomer has three more gauche butane interactions that are... [Pg.142]

Bicyclo[1.1.0]butane is an example of a molecule in which severe angle strain results in decreased stability and greatly enhanced reactivity. The bicyclo[1.1.0]butane ring has a strain energy of 63.9kcal/mol, and the central bond is associated with a relatively high... [Pg.163]

The central C—C bond in bicyclo[ 1.1.0] butane has a high -character and is known to behave as an olefin. Thus, 1-arylsulfonylbicyclobutanes 312 reacted with Grignard reagents in the presence of lithium dialkylcuprates or cuprous salts (Me2S, CuBr or CuCl) giving 3-alkyl-1-arylsulfonylcyclobutanes 313406. [Pg.644]

The central bond of the l-(arylsulfonyl)bicyclo[1.1.0]butane system behaves like the double bond of a, /i-unsaturated sulfones to give alkyl-substituted cyclobutyl aryl sulfones on treatment with organometallic reagents (equation 20)17. This method has been applied... [Pg.767]

The bond between the bridgehead carbons of bicyclo[1.1.0]butanes can be either normal or inverted [35]. The normal bond is stabilized by the high s-character (Scheme 16a). In this case, the hybrids on the bridgeheads Y have low s-character for the bridging Y-X bonds. Electronegative atoms X or substituents R at Y stabilize... [Pg.277]

Tetraphosphabicyclo[1.1.0]butane 58 (Scheme 24) has been reported [60, 61]. The SE is much higher than cyclotriphosphane 14 or P (see Sect. 3.3.4), but stiU lower than bicyclo[1.1.0]butane 45 [62, 63], in agreement with the lone pair effect (see Sect. 2.1.4). Interestingly, the bridgehead bonds have been observed to be shorter than a normal P-P bond (2.218 A in diphosphine) [64]. The related... [Pg.280]

Figure 7.21. Structure of the oxyallyl radical, and the ORTEP representations from X-ray of the bicyclobutanones 45 and 46. Box Schematic representation of the stretch-hond isomerism of bicyclo[1.1.0]butane. (Adapted from ref. 117.)... Figure 7.21. Structure of the oxyallyl radical, and the ORTEP representations from X-ray of the bicyclobutanones 45 and 46. Box Schematic representation of the stretch-hond isomerism of bicyclo[1.1.0]butane. (Adapted from ref. 117.)...
Within the isolobal formalism, the conversion of 47 to 48 is a symmetry-allowed process, if it were to proceed as a concerted reaction (50). Structure 47 represents a transoid-2-meta.Wa-1,3-butadiene. In the bonding description, complex 48 represents formally a 1-metalla-bicyclo[1.1.0]butane. Therefore, the conversion of 47 to 48 represents a thermally allowed, concerted [ 2a + 2S] ring closure, in analogy to the pericyclic ring opening of bicyclo[1.1.0]butanes to give trans,trans-, 3-butadienes. [Pg.65]

The highly enantioselective reductive animation of a-keto acids as a route to amino acids is possible with ligand 118 (3 R,4R)- l-W-benzyl)-3,4-bis(diphenylphosphanyl)pyrrolidine, DEGUPHOS] and [Rh(cod)2]BF4.649 (R,R)-NORPHOS (2-exo-3-endo-bis(diphenylphosphino)bicyclo[2.2.1 ]heptene) and (2. S, 3. S ) - C HIR AP H O S (bis(diphenylphosphino)butane) are also good ligands for this transformation. Arylpyruvic acids give the best results (>95% ee). [Pg.115]

While thermodynamically, the direct metalation of cyclopropane can be envisioned from a synthetic point of view, this approach has been rarely used. A major obstacle appears to be kinetics which can be overcome by incorporation of a hydroxyl group (see Eq. 16)17). In special cases, such as bicyclo [1.1.0] butane and methylenecyclopropane (Eq. 17) 18) the enhanced thermodynamic acidity is aceom-... [Pg.13]

Bicyclic diamines with bridgehead nitrogen 54, 92 BICYCLO[1.1.0]BUTANE, 51, 55 ... [Pg.55]

Sodium, with l-bromo-3-chloro-cyclobutane to give bicyclo [l.l.O]butane, 51, 55 Sodium amalgam, 50, 50, 51 Sodium amide, with 2,4-pentane-dione and diphenyliodonium chloride to give l-phenyl-2, 4-pentanedione, 51, 128 Sodium azide, 50, 107 with mixed carboxylic-carbonic anhydrides, 51, 49 Sodium borohydride, reduction of erythro-3-methanesulfony-loxy-2-butyl cyclobutanecar-boxylate, 51, 12 reduction of 2-(1-phenylcyclo-pentyl)-4,4,6-trimethyl-5,6-dihydro-1,3(4H)-oxazine to 2-(1-phenylcyclopentyl)-4,4, 6-trimethyltetrahydro-l,3-oxazine, 51, 25 Sodium cyanoborohydride, used... [Pg.135]

It was concluded from the formation of a dimer that 598 emerged by a DMS reaction in addition to a bicyclo[1.1.0]butane derivative [248]. The azacydoheptatetraene 599, trapped in an argon matrix kept at -261 °C, was observed by IR spectroscopy after photolysis of 3- and 4-diazomethylpyridine [249]. According to quantum-chemical calculations, the protodebromination of the respective bromodihydrodiazepi-nium ions is believed to proceed via the l,4-diaza-5,6-cycloheptadienes 600 and 601 as intermediates [169, 250],... [Pg.350]

Christl and Lang (390) noticed an upheld signal shift of about 10 ppm when they compared the methine carbon atoms in bicyclo[1.1.0]butane (287) (391) and octavalene (288). On the other hand, in benzvalene (289), the corresponding shielding is +48.3 (203), because in this molecule back-donation from the Walsh orbitals to the ir -orbital of the olefinic group (290) is conceivable. Such an interaction is not possible in 288, because the ir -orbital of the diene chromophore is of different symmetry (390). [Pg.292]


See other pages where Bicyclo butan is mentioned: [Pg.173]    [Pg.1105]    [Pg.243]    [Pg.31]    [Pg.173]    [Pg.1105]    [Pg.243]    [Pg.31]    [Pg.583]    [Pg.163]    [Pg.190]    [Pg.670]    [Pg.896]    [Pg.183]    [Pg.1083]    [Pg.1101]    [Pg.121]    [Pg.249]    [Pg.249]    [Pg.277]    [Pg.278]    [Pg.279]    [Pg.279]    [Pg.105]    [Pg.554]    [Pg.139]    [Pg.169]    [Pg.90]    [Pg.234]    [Pg.808]    [Pg.852]    [Pg.277]   


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Bicyclo butane

Bicyclo butane

Bicyclo butane derivs

Bicyclo butane nitrile

Bicyclo butane radical cation

Bicyclo butane ring

Bicyclo butane, 1-methylcycloaddition reactions

Bicyclo butane, from 1,3-butadiene

Bicyclo butane, reactivity

Bicyclo butanes structure

Bicyclo[1.1.0 butanes, formation

Sodium, with l-bromo-3-chlorocyclobutane to give bicyclo butane

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