74752-52-6Relevant academic research and scientific papers
Stereochemistry of Carbenic 1,2-Vinyl Shifts
Kirmse, Wolfgang,Kopannia, Siegfried
, p. 1178 - 1184 (2007/10/03)
Various 1-phenylbut-3-enylidenes, (Ph)CCR2CH=CHR', were generated thermally and photolytically from tosylhydrazone (diazo) precursors. 1,2-Vinyl shifts, leading to 1,3-dienes, R′CH=CHC(Ph)=CR2, were found to predominate over γ-C-H insertion (R = Me) and to compete with 1,2-H shifts (R = H). Intramolecular addition to the double bond was detected in the case of R = R′ = Me. The resulting bicyclobutane is thermally stable and does not mediate the vinyl shift. Stereospecific migration of 1-propenyl groups (R′ = Me), with retention of configuration, was observed on thermolysis and direct photolysis of appropriate substrates. These data exclude the intervention of a triplet diradical and point to vinyl migration in the singlet manifold. Benzophenone-sensitized generation of the carbenes led to partial stereomutation but did not provide conclusive evidence for a triplet rearrangement (isomerization of the diene products could not be avoided under these conditions).
Vinylcyclopropane Complexes and Vinylcyclopropanes from Benzylidene Complexes and 1,3-Dienes
Fischer, Helmut,Hofmann, Josef
, p. 981 - 988 (2007/10/02)
Benzylidenepentacarbonyl complexes (CO)5M (1) a), OMe (b); M = Cr: R = H (c), OMe (d)>, react with cyclopentadiene by stereospecific transfer of the benzylidene ligand to one C=C bond of the diene and coordination of the resulting endo-6-arylbicyclohex-2-ene (4) to the metal.The (CO)5M fragment occupies the exo-position.Addition of bromide liberates 4 from the metal.The reaction of 1a with 1,3-cyclohexadiene gives the corresponding (endo-7-phenylbicyclohept-2-ene)tungsten complex (6) and, after addition of Br-, the free bicyclic compound.The sequential reaction of 1a with 1,2,3,4,5-pentamethylcyclopentadiene and Br- affords the endo-6-phenyl-exo-4-methyl isomer of pentamethylphenylbicyclohex-2-ene 9 with more than 85percent stereoselectivity.The benzylidene transfer from 1a to cis- and trans-pentadiene, isoprene, and 2-chloro-1,3-butadiene proceeds regiospecifically to the more electron-rich C=C bond to give (E)- and (Z)-phenylvinylcyclopropanes.The E/Z ratio ranges from 0.52 to 2.2.The strucutres of the complexes 3d and 6 were established by X-ray analyses.
