Palladium complexes rearrangement

Palladium-catalyzed oxidation of 1,4-dienes has also been reported. Thus, Brown and Davidson28 obtained the 1,3-diacetate 25 from oxidation of 1,4-cyclohexadiene by ben-zoquinone in acetic acid with palladium acetate as the catalyst (Scheme 3). Presumably the reaction proceeds via acetoxypalladation-isomerization to give a rr-allyl intermediate, which subsequently undergoes nucleophilic attack by acetate. This principle, i.e. rearrangement of a (allyl)palladium complex, has been applied in nonoxidative palladium-catalyzed reactions of 1,4-dienes by Larock and coworkers29. Akermark and coworkers have demonstrated the stereochemistry of this process by the transformation of 1,4-cyclohexadiene to the ( r-allyl)palladium complex 26 by treatment... 

Primary propargylic formates decarboxylate in the presence of Pd(acac)2 and Bu3P at room temperature to give mainly allenic products (Eq. 9.115) [91]. Initial formation of a propargylic palladium complex, which rearranges to the more stable allenylpalladium species, accounts for this transformation. Under similar conditions, a terminal allenyl formate afforded a 99 1 mixture of allene and acetylene product (Eq. 9.116) [91]. However, a mixture of enyne elimination products was formed when a secondary propargylic carbonate was treated with a palladium catalyst (Eq. 9.117). 

Scheme 17.3 Possible stereoisomers of the Jt-allyl (palladium) complex and the equilibrium between them via a it-a-it rearrangement.

The -diene carbomethoxy-palladium complex then undergoes rearrangement to give -allyl carbomethoxy-palladium complex 4. 

Acylation of thiochromanones with boron trifluoride and acetic anhydride readily affords (92), which may be elaborated into (93) (equation 36) (79CJC3292), while conversion of the keto function to an oxime (94) permits the formation of the palladium complex (95) as a first step towards functionalization of the aromatic ring (equation 37) (78BCJ3407), or ring expansion by Beckmann rearrangement (equation 38) (76JCS(P1)2343). 

In the presence of a catalytic amount of palladium(O), silylated vinyloxiranes (310) have been found to rearrange into a-silylated-/I, y-unsaturated aldehydes (312), not only with complete chirality transfer, but also with total retention of the double bond stereochemistry. A mechanism involving a [l,2]-silicon shift from carbon to carbon via a 7r-allylic palladium complex (311) has been invoked358 for the transformation. New... 

Reaction of the bis-olefin 301 with Pd(PPly )4 afforded the isoindoline 302 together with the 1/7-2-benzazepine 303 the former was shown to rearrange to 303 in the presence of the palladium complex (Scheme 39) <1996CC2257>. 

Allylic metals, in propargylic alcohol alkylation, 11, 129 ir-Allylic palladium complexes, and carbocyclization, 11, 426 Allylic position, alkenes, dienes, polyenes, metallation, 9, 6 Allylic selenides, [2,3]sigmatropic rearrangement, 9, 481 Allylic substitution reactions for C-N bonds via amination... 

Asymmetric decarboxylative rearrangement (Carroll rearrangement) of allyl a-acetamido-/3-ketocarboxylates, catalysed by a palladium complex modified with a chiral phosphine ligand, has been reported to give optically active /,5-unsaturated a-amino ketones with up to 90% ee (Scheme 92).135 The mechanism for the Carroll rearrangement is shown in Scheme 93. 

Biich F1M, Binger P, Benn R, Kruger C, Rufinska A (1983) Phosphane-induced, stepwise rearrangement of an octadienediyl palladium complex to seven- and nine-membered metallacycles. Angew Chem Int Ed 22 774-775... 

In the hydrocarbonation of methylenecyclopropanes 8 with nitriles, the hydro-palladation of 8 with 16 gives the alkylpalladium complexes 23 and/or 24 (Scheme 5). The complex 23 would undergo rearrangement by distal bond cleavage to give the Jt-allylpalladium 25 (route A). The reductive elimination of Pd(0) from 25 produces 9. The palladium complex 24 would isomerize to the Jt-allylpalladium complex 27 via proximal bond cleaved ring-opened intermediate 26 (route B). The reductive elimination of Pd(0) from 27 gives 10. 

The Cope- and Claisen rearrangements are also catalyzed by square-planar transition metal complexes. Palladium complexes have been responsible for spectacular increases in the rates of Cope rearrangements by factors of up to 10 . Certain other sigmatropic rearrangements are also catalyzed by transition metal complexes. 

---