Cope Rearrangement and Related Reactions

The rt,/3-unsaturated linear carbonyl compound 39 is obtained by the decomposition of the cyclic hydroperoxide 38 with PdCl2,[35]. The a, 0-epoxy ketone 40 is isomerized to the /3-diketone 41 with Pd(0) catalyst[36]. The 1,4-epiperoxide 42 is converted into the /3-hydroxy ketone 43 and other products[37]. 

The first report on the Pd(II)-promoted Cope rearrangement is the conversion of fw./ra/w-l,5-cyclodecadiene (44) into c/5-l,2-divinylcyclohexane-PdCl2 complex (45) with a stoichiometric amount of PdCl2(PhCN)2 at room temperature. The complex formation is the driving force of this unusual rearrangement [38,39]. A similar transformation of germacrane (l,5-dimethyl-8-isopropyli-dene-/rfflu,/ra j-l,5-cyclodecadiene) takes place[40j. 

The mechanism of the PdCh-catalyzed Cope rearrangement has been studied by use of the partially deuterated 1.5-diene 53[46], The coordination of Pd(II) activates the alkene, and cyclization (carbopalladation) takes place to 

Oxy-Cope rearrangement of 56 to form the cyclic ketone 57 can be carried out at room temperature with catalysis by PdCl2(PhCN)2(47]. 

The PdCli-catalyzed instantaneous rearrangement of A -carbethoxy-S-azabi-cyclo[5.1.0]oct-3-ene (60) takes place at room temperature to give A -car-bethoxy-8-azabicyclo[3.2.1]oct-2-ene (61)[50], The azepine 62 undergoes a smooth skeletal rearrangement to give 63, and the diazepine 64 is converted into the open-chain product[51]. Beckmann fission of the oxime 65 of ketones and aldehydes to give the nitrile 66 is induced by a Pd(0) complex and oxygen [52,53]. 

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Radical cations derived from a variety of hexadiene systems constitute an interesting family of intermediates, since they are related to the potential mechanistic extremes of the Cope rearrangement. The electrocyclic reaction of a hexadiene radical cation has three mechanistic extremes a) addition precedes cleavage (associative mechanism) b) cleavage preceeds addition (dissociative mechanism) c) addition and cleavage occur in coordinated fashion (concerted mechanism). To date, radical cations corresponding to all three mechanistic extremes have been characterized. This illustrates remarkable differences between... 

The rearrangement of modified glycals provides novel strategies to the preparation of C-glycosides. Such reactions involve the sigmatropic mechanisms associated with both Cope and Claisen reactions. In this section, these and related reactions are presented. 

This reaction is related to the Cope Rearrangement and Overman Rearrangement. 

The rearrangements of various allylic compounds catalyzed by both Pd(II) and Pd(0) are treated in this section[491]. Related reactions such as the Carroll rearrangement are treated in Section 2.10.1 and the Pd(II)-catalyzed Cope rearrangement is treated in Chapter 5, Section 3. 

The Claisen rearrangemenC is a thermal rearrangement of allyl aryl ethers and allyl vinyl ethers respectively. It may be regarded as the oxa-version of the closely related Cope rearrangement. Claisen has discovered this reaction first on allyl vinyl ethers 1, and then extended to the rearrangement of allyl aryl ethers 2 to yield o-allylphenols 3 ... 

The 2,4-ct.v relation of the hydroxy and the ester function in both isomers is explained by a cyclization reaction with simultaneous formation of a dioxycarbocation, presumably via a preceding 2-azonia-Cope rearrangement. Treatment with water then provides the observed... 

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