Alkenes from allylic esters

Copper-catalyzed687-689 or photochemical690 reaction of alkenes with peroxy-esters, usually with tert-butyl peracetate (or rm-BuOOH in acetic acid), may be used to carry out acyloxylation or the synthesis of the corresponding allylic esters in good yields. In contrast to the oxidation with Se02, preferential formation without rearrangement of the 3-substituted esters takes place from terminal alkenes 691... 

Copper(I) sulfate generated from the reduction of aqueous copper(II) sulfate with metallic copper promotes the epoxidation of alkenes such as allyl alcohol or propene in low yields.585 The reaction of /-butyl hydroperoxide or /-butyl peracetate with alkenes in the presence of copper(I) chloride results in the homolytic formation of allylic /-butyl peroxides or allylic esters (equations 258-260). 

Ireland-Claisen rearrangements frequently are used for the synthesis of alkenes. This works particularly well if the allyl ester is derived from a secondary allyl alcohol. In this case a stereogenic double bond is formed in the rearrangement. The examples in Figure 14.48 show that the alkene is mostly trans-configured if this C=C bond is 1,2-disubstituted and almost completely is-configured if it is trisubstituted. 

It is possible to perform selenenylation-deselenenylation sequences with only catalytic amounts of selenium species. This reaction sequence provides double bond transpositioned allylic ethers, allylic esters, or allylic alcohols 240 from the corresponding alkenes (Scheme 71). This sequence can be performed electrochemically, and the selenium electrophile is generated from catalytic amounts of diphenyl diselenide.467,468 It has been shown that the electrophilic selenium species can also be generated using diselenides and peroxosulfates together with copper (ii)... 

Nucleophilic attack on ( -alkene)Fp+ cations may be effected by heteroatom nucleophiles including amines, azide ion, cyanate ion (through N), alcohols, and thiols (Scheme 39). Carbon-based nucleophiles, such as the anions of active methylene compounds (malonic esters, /3-keto esters, cyanoac-etate), enamines, cyanide, cuprates, Grignard reagents, and ( l -allyl)Fe(Cp)(CO)2 complexes react similarly. In addition, several hydride sources, most notably NaBHsCN, deliver hydride ion to Fp(jj -alkene)+ complexes. Subjecting complexes of type (79) to Nal or NaBr in acetone, however, does not give nncleophilic attack, but instead results rehably in the displacement of the alkene from the iron residue. Cyclohexanone enolates or silyl enol ethers also may be added, and the iron alkyl complexes thus produced can give Robinson annulation-type products (Scheme 40). Vinyl ether-cationic Fp complexes as the electrophiles are nseful as vinyl cation equivalents. ... 

Allylic esters result from the reaction of alkenes with itri-butyl per-oxyacetate [233], or the more reactive peroxybenzoate [233, 234, 1113], in the presence of cuprous bromide with mercuric acetate [404, or with lead tetraacetate [1114] (equation 127). 

Oxidative acetoxylation provides a direct access from alkenes to alkenyl esters the alkene molecule undergoes replacement of an H atom by an acetate (or generally OCOR) group in its vinylic (v), allylic (a), or homoallylic (h) position according to Scheme 1, where Ox is an oxidant such as O2, Cu p-benzoquinone, and Red a reduced form of Ox such as H2O, Cu hydroquinone. A typical example is the Pd-catalyzed co-oxidation of ethylene and acetic acid to vinyl acetate (eq. (D). 

Alkenes (e.g. camphene) are readily prepared by the BF3,Et20-catalysed elimination of secondary borate esters.Terminal conjugated dienes may be prepared by Pd(OAc)2-PPh3-catalysed elimination from allyl phenyl ethers or allylic acetates [e.g. geranyl, neryl, and linalyl acetates to form similar mixtures of myrcene (60—74%), trans-ocimene (8—20%), and c -ocimene (14—20%)], and the complex [(i7-CsH5)Cr(NO)2]2 dehalogenates n/c-dihalides (e.g. limonene tetrabromide) without affecting other halides (except for benzyl halides). 

More complex products are obtained from cyclizations in which the oxidizable functionality and the alkene are present in the same molecule. y9-Keto esters have been used extensively for Mn(III)-based oxidative cyclizations and react with Mn(OAc)3 at room temperature or slightly above [4, 10, 11, 15], They may be cyclic or acyclic and may be a-unsubstituted or may contain an a-alkyl or chloro substituent. Cycloalkanones are formed if the unsaturated chain is attached to the ketone. y-Lactones are formed from allylic acetoacetates [10, 11]. Less acidic /3-keto amides have recently been used for the formation of lactams or cycloalkanones [37]. Malonic esters have also been widely used and form radicals at 60-80 °C. Cycloalkanes are formed if an unsaturated chain is attached to the a-position. y-Lactones are formed from allylic malonates [10, 11]. yff-Diketones have been used with some success for cyclizations to both alkenes and aromatic rings [10, 11]. Other acidic carbonyl compounds such as fi-keto acids, /3-keto sulfoxides, j8-keto sulfones, and P-nitro ketones have seen limited use [10, 11]. We have recently found that oxidative cyclizations of unsaturated ketones can be carried out in high yield in acetic acid at 80 °C if the ketone selectively enolizes to one side and the product cannot enolize... 

Allylic oxidation. Allylic alcohols are oxidized to enones by Pd(OAc)2 in wet DMF. Allylic esters are obtained from alkene/carboxylic acid mixtures on treat-... 

Homologations. Hydroformylation of S- and O-containing alkenes is mediated by Rh4(CO)i2. Homologous carboxylic acids and derivatives (esters, amides) are obtained from allyl phosphates. ... 

In 1987, Oppolzer and Gaudin reported an intramolecular version of the reaction of a tt-allylpalladium complex with an alkene. The reactions of various 2,6-octadienyl acetate derivatives were achieved in the presence of Pd(dba)2-PPhj at 70-80 C leading to 2-vinyl-1-alkenyUdenecyclopentane derivatives in yields ranging from 20% to 98% (Schemes 4 and 5). With one or two methyl groups attached at the alkenyl terminus, the acyclic alkeny-lallyl acetates under Pd(II) catalysis cycUzed to yield l-alkenyl-2-vinylcyclopentane derivatives (Scheme A 7r-allylpalladium intermediate generated from an allyl ester can... 

Palladium-catalyzed substitutions of allylic esters 129, which proceed via intermediate 7t-allylpalladium complexes such as 130, are well estabhshed [334]. In contrast, the reactions proceeding through [t-allylpalladium intermediates, generated by addition of the palladium a-complex intermediates from haloarenes, haloalkenes, or corresponding triflates, to allene and substituted allenes 131 (Scheme 8.30) have scarcely been tapped [153]. Recently, higher cumulenes have been reported as suitable alkenes in Heck reactions [335],... 

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