ISSN:
1572-9001
Source:
Springer Online Journal Archives 1860-2000
Topics:
Chemistry and Pharmacology
Notes:
Abstract Factors that influence the intramolecular [π2+π2] photochemical ring closure reaction of multiply bridgedsyn-tricyclo[4.2.0.02.5]octa-3,7-diene (2) leading to propella[34]prismane (1) are analyzed. The unfavorable, large increase in strain (89 kcal mol−1) calculated for this reaction is overcome by the favorable ordering of frontier molecular orbitals, which is caused primarily by bridging of the juxtaposed double bonds with trimethylene chains in2. This conclusion is based on detailed analysis of the frontier molecular orbitals (FMO) of cycloocta-1,5-diene (6), cyclodeca-1,6-diene (7), and tricyclo-[4.2.0.02.5]octa-3, 7-diene (3), bridged with alkylene groups of various lengths, in terms of Paddon-Row's theory of through-bond interaction by the use of AM1 semiempirical MO method. In addition to the π-orbital interaction through an even number of C-C bonds, the double-bond-double-bond distance is recognized to be an important factor for the ordering of FMOs. It is suggested that reduction of this distance in6 by only a few tenths of an Ångstrom will change the FMO ordering and allow the intramolecular [π2+π2] cycloaddition to proceed. Potential energy calculations by MM2 indicate that the trimethylene bridges in1 and2 are so flexible that they appear flat on the NMR time scale.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF01374480
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