Benzyl allyl ethers

The hydroalumination of terminal alkenes and dienes using BujAl as aluminum source can also be catalyzed by late transition metal complexes such as (PPh3)2PdCl2 [38]. The reactions are carried out at room temperature, the use of dichloromethane as a solvent is crucial because it probably regenerates the catalytically active Pd(II) species by reoxidizing Pd(0) complexes formed in side reactions. Internal C=C bonds are not hydroaluminated under these conditions. Functional groups such as Cl, Br, and PhS in a position remote to the terminal C=C bond are tolerated, however, certain substrates such as 4-bromo-l-butene, 11-iodo-l-undecene, allyl phenyl ether, allyl benzyl ether, and (3 )-l,3-decadiene did not provide the desired hydroa-... 

Peroxides. These are formed by aerial oxidation or by autoxidation of a wide range of organic compounds, including diethyl ether, allyl ethyl ether, allyl phenyl ether, dibenzyl ether, benzyl butyl ether, n-butyl ether, iso-butyl ether, r-butyl ether, dioxane, tetrahydrofuran, olefins, and aromatic and saturated aliphatic hydrocarbons. They accumulate during distillation and can detonate violently on evaporation or distillation when their concentration becomes high. If peroxides are likely to be present materials should be tested for peroxides before distillation (for tests see entry under "Ethers", in Chapter 2). Also, distillation should be discontinued when at least one quarter of the residue is left in the distilling flask. 

NBS, CH3CN, H2O, 62-90% yield. " The POM group has been selectively removed in the presence of an ethoxy ethyl ether, a TBDMS ether, a benzyl ether, a p-methoxybenzyl ether, an acetate, and an allyl group. Because the hydrolysis of a pentenyl 2-acetoxyglycoside was so much slower than a pentenyl 2-benzyloxyglycoside, the 2-benzyl derivative could be cleaved selectively in the presence of the 2-acetoxy derivative. The POM group is stable to 75% AcOH, but is cleaved by 5% HCl. 

EtSH, BF3 Et20, 63% yield." Benzylamines are stable to these conditions, but BF3 Et20/Me2S has been used to cleave an allylic benzyl ether." ... 

In general the Stork reaction gives moderate yields with simple alkyl halides better yields of alkylated product are obtained with more electrophilic reactants such like allylic, benzylic or propargylic halides or an a-halo ether, a-halo ester or a-halo ketone. An example is the reaction of 1-pyrrolidino-l-cyclohexene 6 with allyl bromide, followed by aqueous acidic workup, to yield 2-allylcyclohexanone ... 

The method is quite useful for particularly active alkyl halides such as allylic, benzylic, and propargylic halides, and for a-halo ethers and esters, but is not very serviceable for ordinary primary and secondary halides. Tertiary halides do not give the reaction at all since, with respect to the halide, this is nucleophilic substitution and elimination predominates. The reaction can also be applied to activated aryl halides (such as 2,4-dinitrochlorobenzene see Chapter 13), to epoxides, " and to activated alkenes such as acrylonitrile. The latter is a Michael type reaction (p. 976) with respect to the alkene. 

In carbohydrate chemistry, the preparation of ethers that are stable in the presence of acids, bases, and aqueous alkali is an important analytical and synthetic tool. The methods used for the etherification of hydroxyl groups51 generally employ reactions of unprotected sugars and glycosides with methyl, allyl, benzyl, triphenylmethyl, and alkylsilyl halides in the presence of a variety of aqueous and nonaqueous bases. 

In addtion to Sm metal, Cp 2Sm(TFlF)B (n = 2 or 0) can be a good starting material for allylsamarium generation. In the case of Cp 2Sm(THF) (n = 2 or 0), allylic ethers are useful precursors since they are able to coordinate to the low-valent lanthanide metal via the internal oxygen. Samarium complexes 45 react with allyl benzyl ether 46 to produce allylsamarium complex 47 and benzyloxide 48 as illustrated in Equation (9).26... 

Allyl and aryl ethers produce carboxylic esters in good yields (60-80%) upon oxidation by benzyltriethylammonium permanganate in dichloromethane [33], e.g. dibenzyl ether gives benzyl benzoate (80%). 

A. J. Colussi, F. Zabel, and S. W. Benson, Very low-pressure pyrolysis of phenyl ediyl ether, phenyl allyl ether, and benzyl methyl-edier and endialpy of formation of phenoxy radical,/ t. J. Chem. 

These ideas will be discussed in the following subsections, where most of the attention will be devoted to the mechanistic smdies with aromatic esters, which have been the subject of an overwhelming majority of the research efforts. Nevertheless, the same reaction mechanism has been shown to be valid for the PFR of anilides, thioesters, sulfonates, and so forth. Furthermore, it is also applicable to the photo-Claisen rearrangement [i.e. the migration of alkyl (or allyl, benzyl, aryl,)] groups of aromatic ethers to the ortho and para positions of the aromatic ring [21,22]. 

A high level of enantioselectivity in an acyclic system has been reported in the rearrangement of tricarbonylchromium(O) complexes of allyl benzyl ethers using chiral lithium amide base 73 (equation 38) . Upon treatment with 1.1 equivalents of lithium amide 73 and 1 equivalent of LiCl at —78 to —50°C, ether 74 afforded the rearrangement product R)-75 in 80% yield with 96% ee. The effect of substituents on the chemical yields and enantioselectivity of the [2,3]-Wittig rearrangement was also studied (see Table 3). 

With the nitrogen atom well protected as the cyclic carbamate 105, all attempts to open the 1,6-anhydro ring under acidic conditions failed owing to the lability of the two allylic benzyl ethers present in the molecule. However, it was possible to debenzylate 105 with lithium in ammonia to form the new cyclic carbamate 108 and acetylation then gave 109. 

Aldehyd Amin = 1 1] HaC -SeH/Ether 20-25°, 10min Allyl-benzyl-amin 92 7... 

The Wittig rearrangement is the base-catalyzed 1.2-shift of an alkyl, allyl. benzyl, or phenyl group of an ether from oxygen to carbon. A patent claim describes the conversion of aryl arylmethyl ethers such as 21 into diarylmethanols such as 22.14... 

Ally lie y benzylic, or tertiary bromides (iodides). Allylic, benzylic, or tertiary alcohols are converted into bromides or iodides by reaction with BF3 etherate and (C2H5)4NBr or (C2H5)4NI in CH2C12 in 60-80% yield. NaBr or Nal can replace (C2H5)4NX in the case of allylic or benzylic alcohols.12 The combination of BF3 etherate and (C2H5)4NX is useful for cleavage of ethers.13... 

Reduction of derivatives of ally lie alcohols. Nickel boride can effect reduction of allylic alcohols to alkenes, but yields are generally improved by reduction of the acetates, benzoates, or trifluoroacetates.1 Reduction of allylic benzyl ethers to alkenes is effected in higher yield with Raney nickel. Methyl ethers are not reduced by either reagent. The trimethylsilyl ethers of allylic alcohols are reduced to alkenes by nickel boride in diglyme.2... 

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