Anti-Bredt bridgehead olefins

The successful inner phase stabilization of cyclobutadiene suggests that this approach may allow stabilization of other molecules with highly strained multiple bonds. An interesting class of hydrocarbons with twisted C=C bonds are anti-Bredt bridgehead olefins. These bicycloalkenes have a trani-cycloalkene and are unstable if their olefinic strain (OS) is OS 21kcalmor. Bicyclo[2.2.2]oct-l-ene 60 and (Z)-bicyclo[3.2.1]oct-l-ene 

A thermal retro-Diels-Alder reaction of 60, which in Jones seminal pyrolysis studies had served as indirect proof for formation of 60, could also be induced inside 4. At 

60 slowly rearranged to triene 65, which escaped the inner phase and was identified in the bulk by its characteristic H NMR specbum. 

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If they were to (3-eliminate, 3.1 and 3.2 would give forbidden anti-Bredt bridgehead olefins because the C=C bond would then be twisted. The ring in 3.3 would have to fold strongly to bring the (3 C-H to the metal, so although not strictly forbidden, 3 elimination would be hard. When the aqua hgand dissociates in 3.6, the vacancy is trans and not cis. 

This result suggests that the anti-Bredt s rule olefin if may be an isolable compound. A number of bicyclic bridgehead olefins (e.g. 52) have recently been prepared, and their stabilities related to the corresponding frans-mono-cyclic olefins 11S>116). The stability of 51 should correlate, then, with the... 

Yes, XIV contains a bridgehead olefin. However, anti-Bredt compounds are not anymore the indiscretions they used to be years ago. Although still strained, they are capable of independent existence at room temperature, so much so that several members of this odd family have been synthesized. Then,... 

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... 

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. 

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