The synthesis of bicyclo[4.4.l]undec-1(ll)-ene (5) by intr,amolecular Wittig reaction is described. The Bredt olefin could not be isolated, but dimerized rapidly to a novel compound 15 containing a cyclopropane ring. The olefin 5 was trapped in situ by 2,5-diphenylbenzo [clfuran.Introduction. -The question of the limits of Bredt's rule is of considerable current interest [l] [2]. It is now generally accepted that the strain of a bicyclic or polycyclic bridgehead olefin (Bredt olefin) is comparable to the strain of the corresponding trans-cycloalkene from which it may be formally derived by bridging. This hypothesis, advocated by Wiseman in 1967 [3], has been supported by experimental evidence from a large number of synthetic approaches to different Bredt olefins and by two independent force-field calculations [4] [S].However, within a series of homologous bridged trans-cyclooctenes, truns-cycloheptenes, and trans-cyclohexenes, the principles which govern relative strain energies are not obvious. Kobrich [l] formulated a rule ('rule A'), according to which increasing the number of carbon atoms in the bridge should decrease the strain of the Bredt olefins. Indeed, whereas the ethylene-bridged truns-cyclo-
The synthesis of 1‐bicyclo[3.2.2]nonene (2) and of 1 (7)‐bicyclo [3.2.2]nonene (3), two isomeric bridged (E)‐cycloheptenes, by intramolecular Wittig reaction is described. These ‘Bredt olefins’ could not be isolated, but dimerized rapidly. In both cases, the main product was shown to be a head‐to‐tail dimer with a cyclobutane ring. The ‘Bredt olefins’ were also trapped in situ with furan or 2,5‐diphenylbenzo [c]furan.
(+)‐Pulegon läßt sich durch Retroaldolisierung stereoselektiv in das (3R)‐Methyl‐cyclohexanon umwandeln und zum Derivat (Ia) bromieren, dessen Tosylhydrazon (Ib) durch Dehydrobromierung in das Azin (II) übergeht und mit Triethylamin zum Hydrazon (III) isomerisiert.
Das Hydroxycyclodecanon (I) wird nach dem angegebenen Schema in das Phosphoniumsalz (VI) übergeführt, das in eine intramolekularen Wittig‐Reaktion zur Titelverbindung (VII) führt, die bei ‐7O ° C NMR‐spektroskopisch untersucht wird.
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