Benzyl ethers generation

The oxidation of p-/ert-butylthiacalix[4]arene or its tetra-O-benzyl ethers generated all four stereoisomers of j-tert-butylsulfinylcalix[4]arenes based on the orientations of the sulfonyl moieties relative the mean plane of the four bridging sulfur centers <03JOC2324>. Alkenes, when treated with W-bromosuccinimide and dimercaptoethane, gave the corresponding... 

A dendritic spacer of poly(aryl benzyl ether) was used for incorporation of phosphine ligands onto a PS resin support [116,117]. Thus, the condensation of 4-(diphenylphosphino)benzoic acid with Wang resin bearing poly(aryl benzyl ether) (generation 1-3) gave the PS-supported dendritic phosphine 86. Treatment of the dendritic phosphine 86 with Pd(dba)2 in THF afforded the bisphosphine-palladium complex 87 (Scheme 29) [ 118]. The PS-supported palladium complex exhibited a positive dendritic influence on the Heck reaction of bromobenzene with methyl acrylate. 

The use of iodotrimethylsilane for this purpose provides an effective alternative to known methods. Thus the reaction of primary and secondary methyl ethers with iodotrimethylsilane in chloroform or acetonitrile at 25—60° for 2—64 hours affords the corresponding trimethylsilyl ethers in high yield. The alcohols may be liberated from the trimethylsilyl ethers by methanolysis. The mechanism of the ether cleavage is presumed to involve initial formation of a trimethylsilyl oxonium ion which is converted to the silyl ether by nucleophilic attack of iodide at the methyl group. tert-Butyl, trityl, and benzyl ethers of primary and secondary alcohols are rapidly converted to trimethylsilyl ethers by the action of iodotrimethylsilane, probably via heterolysis of silyl oxonium ion intermediates. The cleavage of aryl methyl ethers to aryl trimethylsilyl ethers may also be effected more slowly by reaction with iodotrimethylsilane at 25—50° in chloroform or sulfolane for 12-125 hours, with iodotrimethylsilane at 100—110° in the absence of solvent, " and with iodotrimethylsilane generated in situ from iodine and trimcthylphenylsilane at 100°. ... 

It was previously observed that with a catalytic amount of FeCls, benzylic alcohols were rapidly converted to dimeric ethers by eliminating water (Scheme 14). In the presence of an alkyne this ether is polarized by FeCls and generates an incipient benzylic carbocation. The nucleophilic attack of the alkyne moiety onto the resulting benzyl carbocation generated a stable alkenyl cation, which suffer the nucleophilic attack of water (generated in the process and/or from the hydrated... 

Fig. 4. A blue-luminescent poly(phenyleneethynylene) bearing 3rd-generation poly(benzyl ether) dendron as the repeating side groups...

The selective and facile cleavage of the benzylic ether linkages of 1,2,3 or 4 is accomplished by treatment with iodotrimethylsilane to form the corresponding benzylic iodide. Further addition to these iodide derivatives of 1 affords dendrimers of generation 1 with phosphonium ion sites at the periphery. Such a strategy is conducted up to generation 3 with a phosphine or a phosphonium core (Scheme 3). 

Treatment of the elimination product 107 with triethylamine resulted in smooth isomerization of the olefin, to afford the a,p-unsaturated ketone 108. Ally lie oxidation of 108 then generated the secondary alcohol 109 in 72 % yield. The acetonide and silyl ether functions of 109 were cleaved in one reaction to afford a tetraol intermediate that was regioselectively acylated at the secondary alcohol functions, to provide the triacetate 110 in high yield (89 %). Hydrogenolysis of the 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... 

For all three types of dendrimers described above, a flattened, disk-like conformation was observed for the higher generations. However, the molecular shape at the air-water interface is also intimately associated with the polarity, and hence the type of dendrimer used. In case of the polypropylene imine) and PAMAM dendrimers the hydrophilic cores interact with the sub-phase and hence these dendrimers assume an oblate shape for all generations. The poly(benzyl ether) dendrimers, on the other hand, are hydrophobic and want to minimize contact with the water surface. This property results in a conformational shape change from ellipsoidal, for the lower generations, to oblate for the higher generations [46]. 

Poly(benzyl ether) dendrimers have several unique optical and photochemical properties. In particular, it is quite interesting that some photochemical events are considerably affected by the molecular size and morphology of the dendrimer molecules. These examples, together with those by other researchers [2], will provide a new strategy toward next-generation, nanoscopic photofunctional materials. 

Allylic and benzylic ethers can also be cleaved using an arene-catalyzed lithiation, so the corresponding organohthium intermediates could be generated. Thus, different benzylic ethers 49 were hthiated using a catalytic amount of naphthalene (5%) to yield the expected intermediates 50, which after reaction with electrophiles and final hydrolysis gave products 51 (Scheme 16) . ... 

Other Alkyl Ethers. Sucrose has been selectively etherified by electrochemical means to generate a sucrose anion followed by reaction with an alkyl halide (21,22). The benzylation of sucrose using this technique gives 2-O-benzyl- (49%), T-O-benzyl- (41%), and 3 -O-benzyl- (10%) sucrose (22). The benzylation of sucrose with benzyl bromide and silver oxide in DMF also produces the 2-O-benzyl ether as the principal product, but smaller proportions of T- and 3 -ethers (23). Octadienyl ether derivatives of sucrose, intermediates for polymers, have been prepared by a palladium-catalyzed telomerization reaction with butadiene in 2-propanol—water (24). 

Metal salts and complexes have also often been used as redox catalysts for the indirect electrochemical oxidation of alcohols. Particularly, the transformation of benzylic alcohols to benzaldehydes has been studies. For this purpose oxoruthe-nium(IV) and oxoruthenium(V) complexes have been applied as redox catalysts. In a similar way, certain benzyl ethers can be cleaved to yield benzaldehydes and the corresponding alcohols using a di-oxo-bridged binuclear manganese complex Electrogenerated 02(804)3 was used to generated 1-naphthaldehyde from 1-naphthylmethanol... 

Oxidative cleavage by means of electrochemically generated cation-radicals is also possible thus benzyl ethers may be cleaved and carboxylates decarboxylated using cation-radicals of brominated triphenylamines in acetonitrile containing a weak base.34 35 Such as indirect reaction makes it... 

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