Allylic ether cleavage

EtOH, RhCli, reflux, 86% yield. Cleavage proceeds by isomerization and enol ether hydrolysis. See the section on alkyl allyl ether cleavage for other methods to perform the isomerization. 

Allylic substitutions. The catalyt preparation of (V-protected allylic amio cyclic carbamates. Asymmetric a-allj ried out by treating the enamines d (Ph3P)4Pd and subsequent hydrolysis. 1 bonates to l-allyl-2(l//)-pyrimidinonei peptides through ester enolate Claisci set. l-Arylprop-2-enols are suitable fa allyl ether cleavage treatment with a < suffices. 

Allyl ethers can be prepared by reaction of a phenol and the allyl bromide in the presence of base. Several reagents have been used to effect their cleavage ... 

The section on the cleavage of allyl ethers of alcohols should also be consulted. 

Unlike the acid-catalyzed ether cleavage reaction discussed in the previous section, which is general to all ethers, the Claisen rearrangement is specific to allyl aryl ethers, Ar—O—CH2CH = CH2. Treatment of a phenoxide ion with 3-bromopropene (allyl bromide) results in a Williamson ether synthesis and formation of an allyl aryl ether. Heating the allyl aryl ether to 200 to 250 °C then effects Claisen rearrangement, leading to an o-allylphenol. The net result is alkylation of the phenol in an ortho position. 

The reductive cleavage of allyl ethers 28 30 or sulfides is preferred over the metalation of allyl... 

Nickel-bpy and nickel-pyridine catalytic systems have been applied to numerous electroreductive reactions,202 such as synthesis of ketones by heterocoupling of acyl and benzyl halides,210,213 addition of aryl bromides to activated alkenes,212,214 synthesis of conjugated dienes, unsaturated esters, ketones, and nitriles by homo- and cross-coupling involving alkenyl halides,215 reductive polymerization of aromatic and heteroaromatic dibromides,216-221 or cleavage of the C-0 bond in allyl ethers.222... 

The combination of PMHS and Pd(PPh3)4 reduces allyl ethers to propene and alcohols.270 The best combination for the reductive cleavage of ethers appears to be Et3SiH/(C6F5)3B, which gives excellent yields of the alcohol (via the silyl ether) and alkane (Eq. 127).145... 

Allylic amination is important for the solid-phase organic synthesis.15 The solid-phase allylic aminations are devised into the G-N bond formation on solid support and the deprotection of allyl ethers. As a novel deprotection method, the palladium-catalyzed cyclization-cleavage strategy was reported by Brown et al. (Equation (4)).15a,15b The solid-phase synthesis of several pyrrolidines 70 was achieved by using palladium-catalyzed nucleophilic cleavage of allylic linkages of 69. 

In view of the proposed mechanism for this cleavage reaction, it was reasonable to expect that certain allylic ethers for which an elimination pathway existed (Scheme II) would also be susceptible to cleavage under thermolysis, acidolysis or a combination of both. 

Because the reduction potential of ether is usually more negative than that of halides, examples that belong to this category are rather rare. Generally, cathodic reduction of ethers is similar to that of alcohols, and nonactivated ethers are not reducible under the conditions of electroreduction. Activated ethers such as benzylic and allylic ethers are elec-trochemically reduced to a limited extent (Scheme 7) [1, 15, 16]. Reduction of epoxides is usually difficult however, electroreductive cleavage of activated epoxides to the corresponding alcohols is reported [17, 18]. The cleavage of the C—O bond of ethers is more easily accomplished in anodic oxidation than in cathodic reduction, which is stated in Chapter 6. 

Scheme 85 Cleavage of an aryl allyl ether for deprotection of a phenol.

Nickel-catalyzed electroreductive cleavage of the carbon-oxygen bond of allyl ethers has been reported [356], The influence of the nature of the ligands associated to the Ni center tends to determine the chemoselectivity of the above reaction [357]. 

The cationic complex [Ni(bpy)3](BF4)2 is a good catalyst for the electroreductive cleavage of the C—O (allyl) bond of allyl ethers, affording parent alcohols or phenols. The Ni(II)-catalyzed electroreductive deprotection of allyl ethers is found to proceed in a DMF-Bu4NBp4-(Mg) system. For... 

The SmCh-catalyzed electroreductive cleavage of allyl ethers (493) leading to (494) has been performed in a DMF-Bu4NBr-(Mg/Ni) system in the presence of SmCh (10 mol%) in an undivided cell (Scheme 171) [573]. A similar ether cleavage does not proceed in the cases of o-chlorophenyl or o-bromophenyl allyl ethers (495) and the reduction of the Ar— Cl... 

Making use of the same procedure, the ether-functionalized diorganomagnesium compounds 76a-76f were prepared from 3-butenyl ethers and MgH2 (equation 11)"". It should be noted that the addition reaction of allyl ethers to MgHi failed because in that case ether cleavage by MgH2 becomes a competing reaction. Also, for these compounds intramolecular O-Mg coordination in solution was established by NMR spectroscopic studies. 

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