Cycloalkenes bridgehead alkenes

On a similar note, a series of bridgehead alkenes and -cycloalkenes have been reported to undergo cycloadditions with l,l-dichloro-2,2-difluoroethene (12) to give the corresponding dichlorodifluorocyelobutanes.s... 

One may see [2 + 2] cycloadditions of alkenes even when radical-stabilizing groups are lacking if the alkene is of relative high energy cyclopropenes, methylenecyclopropenes, bridgehead alkenes and rrun5-cycloalkenes exemplify the point. 

Kinetic and computational studies by Shea and Kim on MCPBA epoxidations of a series of cyclic alkenes including bridgehead alkenes and tra/w-cycloalkenes have shown that the reactivity depends primarily on the strain energy relief in the transition state <92JA3044>. 

Synthesis of Strained trans-Cycloalkenes and Bridgehead Alkenes via Solvolysis of Bicyclic... 

Shea et al. investigated whether strain involved in alkenes affects reactivity and regiochemistry of the intermolecular 1,3-dipolar cycloaddition reaction [14]. Therefore, the addition of picryl azide (18) with a series of mono-and bicyclic olefins including frans-cycloalkenes and bridgehead alkenes was studied (Scheme 5). In the cases of czs-cyclooctene (16) and ci5-cyclononene (17), decomposition of the initially formed cycloadducts 19 and 20 followed... 

Another group of compounds that have a twisted double bond are the bicyclic compounds with bridgehead double bonds such as 1,2-norbomene (9) and 1,7-norbornene (10). " It has been found that many compounds, such as 11, which is based on trawi-cyclooctene, may be isolated whereas those based on smaller trauj -cycloalkenes are usually quite unstable. Some evidence for the formation of 9 has been obtained by trapping the product of the dehalogenation of 1,2-diha-lonorbornanes." Here, the simplest view is that the two p orbitals that form the double bond in 9 and 10 are roughly perpendicular to each other. However, pyr-amidalization and rehybridization also are involved. One indication is the reduced localized 7i-orbital population found in the NBO analysis. Whereas normal alkenes have 71 populations of 1.96 e, for 9 with OS = 57 kcal/mol, it is 1.921, and for 10 with OS = 86 kcal/mol, it is 1.896. With 9, the deviations of the a and n orbitals from the line of centers are 24° and 19°, respectively, and with 10, the deviations are 34° and 29°. 

Strained n/d/ -Bredt alkenes as well as -cycloalkenes will undergo [2 + 2] cycloadditions with alkenes. The bridgehead bicyclo[3.3.1]nonenones 16, produced as a transient species by the dehydrobromination of the corresponding bridgehead bromoketone, undergo cycloaddition with 1,1-dimethoxyethenc (15) to give the tricyclic ketones 17 in quantitative yields.7... 

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