The Photochemistry of Conjugated cis-Bicyclo[5.l.0]octenones, cis-and trans-Bicyclo[5.2.0]non-2-en-4-ones, and Their Methylene AnalogsThe photochemistry of 1,4,4-trimethyl-cis-bicyclo [5.1.0] oct-5-en-Z-one, cis-bicyclo [5.1 .O] oct-Z-en-4-one, and their methylene derivatives has been studied. In the first instance, 1,3 shift of the bond common to the two rings occurs, with rearrangement occurring from the singlet manifold. Photoisomerization of its methylene derivative likewise is a singlet state transformation. In sharp contrast, although the 2-en-4-one bicyclic and the derived conjugated diene also undergo excited state vinylcyclopropane-cyclopentene bond reorganization, these reactions proceed readily from the respective triplet states. These differences have been rationalized in terms of conformational factors particularly as they relate to bond overlap in the SI or the transoid (ix., as relates to Tbond overlap) TI states. The cis-and trans-bicyclo[5.2.0] non-2-en-4-ones, as well as their methylene congeners, do not exhibit an analogous propensity for rearrangement. Rather, polymerization was noted in aprotic solvents throughout this latter series.(31) R. S. Mulliken and C. C.
Kinetic deuterium isotope effects have been determined for the Ag+-catalyzed rearrangements of 1,7dideuterio-(lb), 1 -deuterio-7-methyl-(3b), and 1 -trideuteriomethyltricyclo[4.1.0.0 2'7]heptanes (8). Dideuterio analog la exhibited a faster rate of isomerization to 1,3-cycloheptadiene-2,3-d2 than its protio counterpart, thereby giving rise to an inverse fractionation factor (ks/kv = 0.847). A similar rearrangement of 3b revealed that the isomeric ethylidenecyclohexenes 4b and 5b as well as 2-methylcycloheptadiene 6b were also produced under the control
Silver(I) Ion Catalyzed Rearrangements of StrainedBonds. IV. The Fate of Tricyclo[4.1.0.02'7]heptane1,2 Sir:Earlier studies in this laboratory have elaborated upon the remarkable facility with which Ag+ can induce thermally disallowed [,2a + "2a] skeletal isomerizations of homocubyl and 1,1'-bishomocubyl systems.1•3 We (1) Paper III: L. A. Paquette and J. C. Stowell, submitted for publication.(2) Acknowledgment is made to the donors of the Petroleum Research Fund, administered by the American Chemical Society, for their partial support of this research.
The kinetics of hydrolysis of the four possible stereoisomeric tricyclo[4.2.0.01 2' 4]octan-5-yl 3,5-dinitrobenzoates and p-nitrobenzoates in 80 % aqueous alcohol have been studied at several temperatures. A striking feature of the present results is the convergence of both pairs of isomers to two related but noninterconverting cations (51 and 52), only the latter of which is capable of cyclobutane ring opening or ring expansion for stereoelectronic reasons.Both 1 a,2j3,4/3,6a-dinitrobenzoates gave identical product mixtures (after 10 half-lives) consisting of exo-cisbicyclo[4.2.0]oct-2-en-5-ol (21a) and its internally returned ester 21b. Ionization in the la,2a,4a,6a series led to formation of the epimeric m-bicy clo[3.3,0]oct-2-en-6-ols (26 and 27, 52-58%), e/itfo-rá-bicyclo[4.2.0]oct-2-en-5-ol (28, 33-41%), and the alcohols of retained tricyclic structure (17 and 20, 7-9%). The formation of the [4.2.0] bicyclic alcohols with hydroxyl orientation inextricably linked to a specific precursor geometry implicates a rigid cation geometry and highly directed discharge by solvent. Studies of the products obtained from hydrolysis of deuterium labeled ester 42 showed the absence of deuterium scrambling and excluded the operation of cyclopropylcarbinyl-cyclopropylcarbinyl rearrangement. Carbocationic leakage of the homoallylic -> allylic type was also not in evidence. A connection is drawn between various [3.1.0] bicyclic systems and the reactivity features of these molecules are discussed. Further consideration is given the general questions of bisected bishomoallylic cation intervention and of cyclobutane neighboring group involvement.
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