Palladium catalysts Cope rearrangement

The [3,3]-sigmatropic rearrangement of a 1,5-hexanediene is known as the Cope rearrangement and usually proceeds through a chair transition state. Generally, a large substituent at C-3 (or C-A) prefers to adopt an equatorial-like confirmation.303 304 As the reaction is concerted, chirality at C-3 (or C-4) is transferred to the new chiral center at C-l (or C-6). The reaction can be catalyzed by transition metals.305 The use of a palladium catalyst allows for the reaction to be conducted at room temperature instead of extremely high temperatures (Scheme 26. lO).306-307... 

The Cope rearrangement takes place with hydrocarbon substrates. Nickel(O) and palladium(II) species were first demonstrated to show opposite effects in the rearrangement, the nickel(O) catalyst being responsible for ring expansion (equation 28) and the palladium(n) complex for ring contraction (equation 29). The reaction shown in equation (29) is catalyzed less effectively by H2[PtCl4]. 

Palladium(O) complexes also catalyse the low-temperature 3-aza-Cope rearrangement of A -allylenamines in the presence of trifluoroacetic acid as co-catalyst (Scheme 15). 

The Cope rearrangement of germacrane-type precursors can also be achieved by stoichiometric amounts of a palladium(II) catalyst, e.g., rearrangement of 28 to 29l04-. 

Dienes undergo Cope rearrangement in the presence of palladium catalysts. 

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