Palladium(II)-Catalyzed Rearrangement and Oligomerization Reactions of cis-Bicyclo[4.2.0]oct-7-ene

Abstract

In the presence of several Pd(II) catalysts, cis-bicyclo[4.2.0]oct-7-ene (4a) was found to undergo olefin isomerization ("ring walking") and oligomerization, resulting in the formation of cis-bicyclo[4.2.0]oct-2-ene (4d) and the low-molecular-mass cycloaliphatic oligomers 5a−d, respectively. The catalysts studied are [Pd(NCEt) 6), and [(2,9-dimethyl-1,10-phenanthroline)Pd(CH 3 )(NC(CH 2 ) 6 CH 3 )][SbF 6 ] (7). Isomerization included the formation of both 4d and the olefinic end groups of 5a−d and ranged from 94% using catalyst 7 to 29% employing catalyst 2. Ab initio and DFT calculations at the LMP2/6-31G** and B3LYP/6-31G** levels show that the thermodynamic stabilities of the bicyclo[4.2.0]octene isomers increase in the order 7-ene 4a < 1(8)-ene 4b < 1-ene 4c ≈ 1(6)-ene 4e ≈ 3-ene 4f < 2-ene 4d. A mechanism of isomerization via subsequent β-hydride eliminations and olefin reinsertions is proposed. These results are in contrast to the reactions of bicyclo[3.2.0]hept-6-ene (3a) catalyzed by 1, 2, and 7 and the reaction of 4a catalyzed by Cp 2 ZrCl 2 / MAO (Cp = η 5 -C 5 H 5 ), all of which produced polymers in good yields (73−99%).

Ru-Catalyzed Isomerization Provides Access to Alternating Copolymers via Ring-Opening Metathesis Polymerization

“…Their calculations show the bond migration from the 6-position to the 1(7)-position is endothermic by more than 9 kcal/mol. 40 As noted above, regioisomer 4 ′ is not formed upon addition of catalyst 2 to amide 4 is not isomerized by catalyst 2 .…”

Palladium-catalysed alkene chain-running isomerization

“…Such transition metal-catalysed transformations have been extensively studied and recent investigations have achieved regio- and diastereoselective control. 3,4 …”

“…5 Isomerization alone can afford either a kinetic or a thermodynamic product of double bond migration. 3,4 In the case of kinetic control, linear terminal alkenes are often selectively converted to 2-olefins. 4 Long-distance chain-running double bond isomerization has been achieved using palladium or nickel catalysis, but it often takes advantage of a thermodynamic driving force to convert the alkene selectively to another functionality such as ketone or aldehyde.…”

“…The isomerization of 1-hexene produces a mixture of 2-hexenes and 3-hexenes in nearly a thermodynamic ratio (entry 5). 3 l Isomerization of the disubstituted olefin (entry 6) efficiently produces the trisubstituted alkene.…”

“…9 While transition metal-catalysed isomerization of O -silylated unsaturated alcohols has been reported previously, only a very limited number of substrates have been investigated. 3 i ,4 d , k ,6 Most of the literature examples involve conversion of an unsubstituted allyl moiety to an enol silane functionality.…”