Ethers allyl benzyl ether

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. 

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 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... 

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. 

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... 

Cyclization of allylic alcohols to form epoxides has been particularly problematical, and the reactions have been more of mechanistic than of synthetic interest. For reactions conducted under basic conditions, it is possible that epoxide formation involves initial halogen addition followed by nucleophilic displacement to form the epoxide. Early examples of direct formation of epoxides from allylic alcohols with sodium hypobromite," bromine and 1.5 M NaOH,12 and r-butyl hypochlorite13 have been reviewed previously.fr Recently it has been shown that allylic alcohols can be cyclized effectively with bis(jym-collidine)iodine(I) perchlorate (equation 3).14 An unusual example of epoxide formation competing with other cyclization types is shown in equation (4).15 In this case, an allylic benzyl ether competes effectively with a -/-hydroxyl group as the nucleophile. 

Various metal catalysts accelerate the allylation of carbonyl and imine substrates. Triethylborane induced the addition of allylbenzoates, -phenyl ethers, and -benzyl ethers in the presence of Pd(PPh3)4 (Equation (153)).619... 

Selenium dioxide converts aryl and aralkyl allyl ethers into aldehydes and the corresponding alcohols. Allyl benzyl ether refluxed with selenium dioxide in acetic acid and dioxane for 1 h gives a 50% yield of benzyl... 

The cyclization is highly stereoselective according to Beckwith s radical cyclization rules [73]. Thus, the allylic benzyl ether 41 (a 1 1 mixture of diastereoisomers) undergoes a... 

As noted in Section 3.11.1, some of the earliest mechanistic work on the 2,3-Wittig rearrangement was carried out with allyl benzyl ethers. Selective benzyl deprotonation is typically effected with n-butyl-lithium in THF or THF-TMEDA at low temperature. Rautenstrauch s studies, summarized in Table 8, clearly showed that lower temperature favors 2,3- over 1,2-rearrangement, and established the potential... 

Table 8 2,3-Wittig Rearrangement of Allyl Benzyl Ethers...

Acylations. Catalyzed by graphite the Friedel-Crafts acylation as well as the transformation of ethers to esters by acyl halides in refluxing 1,2-dichloroethane are realized. Although aliphatic chlorides are inferior to aromatic halides this method is quite general as shown by the synthesis of benzoates (e.g., allyl benzoate from allyl benzyl ether and methyl benzoates from methyl f-butyl ether). 

V K lation as well as the uv -.L 1,2-dichloroethane are k "..i.ides this method is quite r/.. ite from allyl benzyl ether... 

Cone conformations are established when 48 is converted to its tetra-allyl ether 51c, benzyl ether 5Id, or trimethylsilyl ether 51 e, when 47 is converted to its... 

Phenyl ethers—see Alkyl phenyl ethers, Allyl phenyl ethers, Benzyl phenyl ethers, 2-Hexenyl phenyl ether PhenyUiydrazones, thermochemistry of 252 PhenyUminobenzoxathiole, photoreactions of 1075... 

Pyridinium chlorochromate oxidation of an allyl ether or benzyl ether gives the enone (CH2CI2, reflux, 84% yield). ... 

Mannich-type cyclizations of vinylsilanes have found considerable application in the area of alkaloid total synthesis. Cyclizations that occur in the exocyclic mode with respect to the vinylsilane nucleophile have been widely employed to assemble 3-alkylidenepiperidine substructures with high stereocontrol. Overman and coworkers have made extensive use of the acid-promoted conversion of bicyclic oxazolidines to alkylideneindolizidines in their total syntheses of pumiliotoxin A alkaloids (Scheme 36). - " - An illustration of the mild nature of iminium ion-vinylsilane cyclizations is provided in the conversion of (101) to (102), the penultimate precursor of (-i-)-pumiliotoxin A. This conversion was accomplished in 71% yield by heating (101) at 80 C in a methanolic pyridine-pyridinium tosylate buffer (pH 4.5). More strongly acidic conditions had to be avoided since they led to competitive solvolysis of the allylic benzyl ether functionality of the pumiliotoxin A side chain. To the limits of detection by high... 

Similarly, ohgocycles are obtained from appropriate allyl benzyl ethers as outlined with representative examples in Scheme 21.i i Stereochemical aspects of Pd-catalyzed cyclizations in connection with the synthesis of pancratistatin and related natural products have been studied intensively (second reation in Scheme 21). ... 

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