Michael F. Rettig

Palladium(II) catalyzed rearrangement of bicyclo[6.1.0]- non-4-ene to cis,cis-1,5-cyclononadiene

Abstract PdCl2(PhCN)2 reacts with bicyclo[6.1.0]non-4-ene, (I), in non-polar solvents to produce dichloro-cis,cis-1,5-cyclononadienepalladium(II) as the final product. The reaction involves cyclopropyl CC and CH bond cleavages in (I) to produce the isomeric diene. The reaction proceeds by cis addition of PdCl to a strained CC bond, followed by a stereospecific 1,2 hydrogen migration and PdCl elimination. PMR and chemical evidence is presented in support of the PdCl addition. The reaction reported is synthetically useful for the preparation of both cis,cis-1,5-cyclononadiene and trans-bicyclo[6.1.0]non-4-ene, the latter being obtained on quenching the reaction mixture at short times.

Reactions of bicyclic cyclopropanes and bicyclic cyclobutanes with dichlorobis(benzonitrile)palladium(II)

Abstract Exo - and end o-9-methylbicyclo[6.1.0]non-4-enes react with dichlorobis(benzonitrile)palladium(II) to produce initially the isomeric dimeric (chlorine bridged) π-complexes, (PdCl 2 - C 10 H 16 ) 2 . The π-complexes rearrange within minutes in solution at room temperature to produce stereospecifically the chlorine bridged dimeric trihapto-σ,π-cyclooctenyl complexes which result from chloropalladation of the external cycopropane carbon—carbon bond, with chlorine bound at the carbon bound to methyl. The chloropalladations also occur during several hours at 75°C in the solid state. The σ,π-cyclooctenyls react with cyanide ion to produce quantitatively 9-methyl- trans -bicyclo[6.1-0]non-4-ene, which hydrocarbon was also independently synthesized. The trans -fusion in the product of cyanide displacement implies an inversion at carbon along the reaction pathway. The relationship of this chemistry to cyclopropane oxymercuration is discussed. The cyclobutane containing hydrocarbon bicyclo[6.2.0] dec-4-ene was incorporated in a π-complex similar to those above. The cyclobutane moiety was found to be inert to chloropalladation under mild to moderate conditions.

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Dichlorobis(organonitrile)palladium(II) catalysis of cis- to trans- isomerization of ethylchrysanthemate and chrysanthemic acid

Complexes of the type L2PdCl2 (L = CH3,CN, CH3CH2CN, PhCN) in benzene or chloroform act as homogeneous catalysts in the room temperature cis to trans isomerization of ethylchrysanthemate and chrysanthemic acid.

Formation of cyclopropane rings via Zr—X (X = Cl, Br) γ-elimination

Abstract (η-C5H5)2Zr(Cl)H (I) reacts with 4-chlorocyclohexene and 4-bromocyclohexene to give moderate yields of bicyclo[3.1.0]hexane. Reaction of I with 4-chloropent-1-ene gives low yields of cis- and trans-1,2-dimethylcyclopropanes, 42% trans-pent-2-ene, and no cis-pent-2-ene. Reaction of I with 2-methyl-3-chloropropene gives 31% methylcyclopropane. Formation of these rings is believed to proceed by ZrX (X = Cl, Br) γ-elimination. Side reactions include (1) ZrX β-elimination to yield halogen-free olefins and (2) formation of halogen-free olefins by direct reduction of CX by ZrH.

Reactions of palladium(II) halides with 7-methylenebicyclo[2.2.1]hept-2-ene derivatives; unique trans-halogenopalladation of the exocyclic double bond

7-Methylenebicyclo[2.2.1]hept-2-ene and its derivatives are unusual in that the two double bonds are crossed. In contrast to the behaviour of most non-conjugated dienes toward palladium(II), these dienes do not form stable chelated diolefin complexes. Instead, in solvents of low polarity, halogen-bridged dimeric 2–3η-{(bicyclo-[2.2.1]hept-2-en-7-yl)methyl} chelates are formed, in which C(7) is bound to either Cl, Br, or MeO (the latter if methanol is present in the reaction mixture). In the absence of methanol, the very fast overall reactions involve trans-addition of palladium and halogen to the exocyclic olefin, with co-ordination of the remaining double bond. The trans-addition must occur either by an ionic or a bimolecular path. In any event the facility for trans-halogenopalladation observed here suggests that cis- and trans-halogenopalladations of organic substrates may in general be competitive.