Ketones, 3- Cope rearrangement

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]. 

This reaction, called the oxy-Cope rearrangement has proved highly useful in synthesis." The oxy-Cope rearrangement is greatly accelerated (by factors of 10 -10 ) if the alkoxide is used rather than the alcohol.In this case the direct product is the enolate ion, which is hydrolyzed to the ketone. 

Bicyclic ketone (33) was needed for a chrysanthemic acid synthesis. tarbene disconnection next to the ketone group (Chapter T30) reveals y. (5-unsaturated acid (35) as an intermediate, available by a Claisen-Cope rearrangement. 

In the reaction of disubstituted alkynes, 1,3-migration of the acetate takes place to give allenyl esters that can be versatile substrates, especially for [3,3]-Cope rearrangements.333 1,5-Enynes have proved to be versatile substrates for the preparation of perfumery agents such as sabinol334 and sabina ketone.335 Transannular systems undergo similar reactions.336... 

The bicyclic ketone (555) was treated with cyclopentenyllithium (354) at —78 °C to form the intermediate (555), which underwent a rapid Cope rearrangement to the intermediate (356). By treatment of (356) with methyl iodide, compound (357) was obtained. The ketone (357) would serve as an intermediate in the synthesis of ophiobolin A (358) 124). 

Stereocontrolled oxy-Cope rearrangement. 1,2-Addition of a chiral vinyl-lithium reagent to a chiral (3,-y-unsaturated ketone could give rise to at least eight... 

In the total synthesis of cerorubenic acid-III methyl ester (105), diene 102 was converted to enantiopure tricyclic ketone 103 through an anionic oxy-Cope rearrangement (equation 56)82. Conversion of 102 to 103 afforded the entire ABC substructure of 104 and 105, most notably the double bond occupying a bridgehead site. 

Rigid polycarbocyclic isomeric ketals 515 and 516 undergo a Cope rearrangement to afford the diketones 517 and 518 on heating in a H2O-THF mixture at 55 °C in the presence of p-TsOH (equations 199 and 200)256. The rearrangements of bridged ketones... 

An interesting approach to form a divinylcyclopropane structure capable of rearranging into seven-membered functionalized derivatives consists of the silyloxylation of cyclic ketones 541 followed by a spontaneous Cope rearrangement to produce the cyclic enol esters 542 which then hydrolyzed to ketones 543 (equation 2 1 3)265. 

With respect to the above-mentioned unsaturated carbonyl compounds with a double bond and a carbonyl group separated by three carbon atoms (14), it can be stated here that they may be disconnected to an alkyl vinyl ketone and an allylic anion (Scheme 7.5), through an oxy-Cope rearrangement (C/. Scheme 5.22). 

The Cope rearrangement of 24 gives 2,6,10-undecatrienyldimethylamine[28], Sativene (25j[29] and diquinane (26) have been synthesized by applying three different palladium-catalyzed reactions [oxidative cyclization of the 1,5-diene with Pd(OAc)2, intramolecular allylation of a /i-keto ester with allylic carbonate, and oxidation of terminal alkene to methyl ketone] using allyloctadienyl-dimethylamine (24) as a building block[30]. 

The 5-9-5 skeleton was assembled by the addition of the alkenyl cerate derived from 6 with the ketone 4, to give 7. -Cope rearrangement then gave the 5-9-5 enolate, which was quenched with methyl iodide to give 8. The ketone 8 underewent spontaneous intramolecular ene cyclization, to give 9. 

Reaction of vinyl Grignard reagents with a-halo ketones. Vinylmagnesium bromide or vinyllithium (2 equivalents) reacts with a-halocycloalkanones to give 1,2-divinylcycloalkanols, used in oxy-Cope rearrangements for synthesis of large ring ketones (c/ 7, 302-303 8, 412 414).8 Examples ... 

---