Anti-Bredt olefins

Compounds with at least one stereogenic center and one stereogenic axis (this also includes anti-Bredt-olefins that exist in two stable atropisomeric forms). 

The ionization potential, 8.69 eY, is lower than in the case of -cyclooctene (8.98 eV) or cyclohexene (9.12 eV), as expected. The highly strained anti-Bredt olefin, 11-bromo-e/ -9-chloro-7-ethoxybicyclo[5.3.1]undec-l(ll)ene has been synthesized and its struc-... 

Anomeric effect, 82, 310-311, 305 Antarafacial, 163 examples, 164 sigma bonds, 167 Anti-Bredt olefin, 102 Approximations of MO theory Born-Oppenheimer, 22 Hartree-Fock, 222 Huckel, 35, 86 independent electron, 35 LCAO, 229 nonrelativistic, 22 SHMO, 87... 

Twist as well as pyramidalization are the typical deformations of bridgehead double bonds in bicyclic compounds of type 44 (Table 4). Structures of the type 44 comprise Bredt-olefms (formerly called anti-Bredt-olefins) and bridgehead olefins. In Bredt-olefins, the double bond is located at the bridgehead of a bicyclo[m.n.o]alkane skeleton with m,n,o 1, whereas... 

Given the need for photoactivation, an often encountered additional requirement for substrates participating in DPM reactions is the presence of a strong chromophore as provided, for example, by the presence of a phenyl group on at least one of the double bonds. In acyclic 1,4-dienes, the central sp -hybridized carbon normally needs to be tetrasubstituted otherwise, competing 1,2-hydrogen shifts can occur. This requirement does not apply, however, to those cyclic substrates where isomerization would lead to an anti-Bredt olefin (as would be the case for the conversion of barrelene to semibullvalene, 6 7, shown in Scheme 9.2). 

The epimeric 2-hydroxymethyl-5,6-exo-trimethylenenorbomanes on reaction with sulphuric acid in pentane yield 4-homoisotwistane (811). Seychellene, which possesses the homoisotwistane skeleton, on conversion to its unstable epoxide, which was stored in the presence of light and air before reduction with LiAlH4, was transformed into the abnormal oxidation product norseychelanol (812) a scheme based on dioxetan formation was proposed. Bromination or Koch-Haaf carboxylation of (811) produces the appropriate 3-substituted derivative, indicating that C-3 in (811) is at least as reactive as the 1-position in adamantane, while the 1- and 8-positions in (811) are unreactive. The 3-bromo-derivative (813) is solvolytically more reactive than 1-bromoadamantane, and reaction with sodamide in boiling toluene yielded the anti-Bredt olefin (815) which could be isolated in 52% yield (815) exhibited typical... 

Several papers have appeared dealing with the synthesis of strained bridgehead olefins (anti-Bredt olefins). Conditions are described whereby a 10 1 mixture of the olefins (25) and (26) is formed by the vacuum pyrolysis of the bridgehead chloro-compound (24). ° The olefin (25) can form a reversible stabilized complex with [Pt°(PPh3)2], and this same catalyst can also effect irreversible isomerization to (27). The lead tetra-acetate-induced oxidative decarboxylation of the propellane carboxylic acid (28) produces the stable olefin (29) in good yield. ... 

An intramolecular Wittig reaction has given the first optically active anti-Bredt olefin (30) with known absolute configuration. The diolefin (31) is thermally labile, and isomerizes to (32) with a half-life of 314 min at 25 °C. The interesting bridgehead olefins (33) and (34) have not been isolated, but have been characterized as their Diels-Alder adducts, or dimers, respectively. 

The first two would give forbidden anti-Bredt olefins if they were to -eliminate. 

The chemistry of lithium carbenoids has been reviewed by Kobrich, who has also reported the preparation of the anti-Bredt olefin (65). The vinylidene carbenoid, which was generated by reaction of (64) with methyl-lithium,... 

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