Subject allyl ethers

Examination of the stereospecificity of the etherification indicated that the reaction was subject to a dramatic halide effect (Tab. 10.9). Treatment of enantiomerically enriched allylic carbonate (R)-53 (94% ee) under optimized conditions furnished the allyl ether (R)-54 in 84% yield (2° 1° >99 1), although with poor enantiospecificity (41% cee ... 

In 2002, Grubbs and co-workers reported the first CM reactions of allyl phosphines.In an initial reaction, subjecting allyl diphenylphosphine to catalyst 5 (5 mol%) failed to produce any of the desired cross-product. However, by protecting the phosphine as its borane complex, CM reactions could be achieved in good yield with high E-selectivity (Equation (5)). Notably, catalyst 5 failed to dimerize borane-protected vinyl diphenylphosphine. This result was attributed to substrate trapping of the catalyst as an unreactive Fischer carbene, a situation analogous to that observed in the CM reactions of alkyl vinyl ethers. 

Allyl Ethers of Carbohydrate. A number of compds, such as allyl glycerol, allylglycol, allyl mannitol, allylsorbitol, all yl pent a-erythritol, etc were prepd during and after WWII by Nichols Yanovsky. They also discussed previous work on this subject and listed several refs. According to them the first compd of this type was triallyl-glycerol prepd in 1856 by M.Berthelot S. de Luca... 

A number of organoselenium reagents have been used as efficient initiators of ring closure, leading from unsaturated substrates to the lactones and cyclic ethers (81T4097). The reaction is termed phenylselenoetherification. The phenyl selenoethers obtained are subject to a selection of transformations, e.g. their conversion to allylic ethers (Scheme 50) and their... 

On another front, the mixture of allylic alcohols 512 and 513 was converted by reaction with methanesulfonic acid anhydride in the presence of triethylamine to a mixture of the corresponding mesylates, which were subjected collectively to methanolysis to afford 514, and none of the allylic ether epimeric at C-3 was isolated. N Debenzylation of 514 followed by a classic Pictet-Spengler cyclization then afforded ( )-buphanisine (361) (208). 

Allyl ethers of enols and phenols undergo rearrangement to C-allyl derivatives when heated to sufficiently high temperatures. The reaction, named after its discoverer (Claisen, 1912), was first observed when ethyl O-allylacetoacetate was subjected to distillation at atmospheric pressure in the presence of ammonium chloride.1 2... 

When propargyl allyl ethers are subjected to transition metal-catalyzed enyne cyclization reactions, 3-alkylidene-substituted tetrahydrofurans are usually formed. A useful variation of this scheme is the Pd(0)-catalyzed tandem enyne cyclization/Suzuki coupling reaction with various arylboronic acids (Equation 90) <2005JOC1712>. The stereoselectivity of this reaction is explained by invoking a chairlike transition state. 

As in the case of the / -series, the a-anomer with a free hydroxy group at C2 also showed good diastereoselectivity (13 1) in the Simmons-Smith cyclopropanation with diethylzinc/ diiodomethane in fert-butyl methyl ether at 0 C. Several substituted allylic ethers, e g. 70, were subjected to this reaction with success. While the auxiliary can be easily removed by a ring-contraction method to give cyclopropylmethanol derivatives, this methodology provides an efficient method to prepare both enantiomers. 

The intramolecularity of the Claisen rearrangement had been established by Schmid and Schmid (1952) in an experiment in which 46, labeled with carbon-14, was mixed with unlabeled 2-carbomethoxy-6-methylphenyl allyl ether, and subjected to the conditions of thermal rearrangement. Both reactants had previously been shown to rearrange smoothly and at similar rates to yield para-rearrangement products. The reaction products were separated, and it was found that no interchange of carbon-14 had occurred, and thus that both rearrangements were intramolecular. 

In 1985, O Malley et al. published the total syntheses of rac-averufin (103) and rac-nidurufin (104) (65). These are both early precursors of the aflatoxins in their biosynthesis. Nidurufin (104) is the direct successor of averufin (103) and the direct precursor of versiconal hemiacetal acetate (12, see Scheme 2.1). Nidurufin (104) and averufin (103) are accessible by the same synthesis route only the two last steps differ firom each other (see Scheme 2.17). The first reaction was a double Diels-Alder reaction with dichloro-p-benzoquinone (97) and two equivalents of diene 98. Then, three of the four alcohol functions were selectively MOM-protected (—> 99). The remaining alcohol was converted into the allyl ether and then subjected to a reductive Claisen rearrangement, followed by MOM-protection of the redundant alcohol ( 100). By addition/elimination of PhSeCl, 101 was formed. Deprotonation of t-butyl 3-oxobutanoate, followed by reaction with 101 yielded the pivotal intermediate 102. This could be converted into rac-averufin (103) by deprotection of the alcohols and decarboxylation at the side chain. The last step was a p-TsOH-catalyzed cyclization to give 103. By treating 102 with /m-CPBA, the double bond is epoxidized. rac-Nidurufin (104) was then formed by cyclization of this epoxide under acidic conditions. 

Building upon this promising chemistry, Stoltz and coworkers [50] extended the scope of the mild oxidation system to the formation of other cyclic compounds - specifically, benzo-furans and dihydrobenzofurans. Aryl allyl ether 142 was subjected to the Pd(OAc)2/ethyl nicotinate catalyst under a variety of oxidants to provide benzofuran 144. Presumably, this reaction proceeds by initial palladation, followed by alkene insertion and )3-hydride elimination to form vinylic intermediate 143, which then isomerizes to the more thermodynamically stable benzofuran 144. Although molecular oxygen was a suitable oxidant for this reaction (Table 9.2 entry 1), benzoquinone appeared to be the optimal reoxidant (Table 9.2 entry 2), providing the highest overall yields. 

Danishefslqr and coworkers eirployed the [2,3]-Wtittig rearrangement in their synthesis studies toward the xenibellol core through tributylstannylmethyl allyl ether 20, prepared from 19. They subjected 20 to the rearrangement conditions with n-BuLi in THE at -78 °C to rt for 12 h... 

In the same manner, also related branched allyl ethers were subjected to similar reaction conditions (Table 6.5) [186,187]. 

The same catalytic system also performed well in the hydroalkoxylation of allenes where the C-O bond was formed at the least hindered terminal carbon of the allene. This report was later the subject of a DFT study by Maseras and Patton. Interestingly, it was found that the addition of the alcohol likely occurred, in fact, at the most hindered carbon and was followed by a second hydroalkoxylation of the allylic ether and subsequent elimination, the whole process accounting for the observed regioselectivity. This second addition could nevertheless be impeded through appropriate choice of reaction conditions (i.e. DMF as solvent at 0°C with 10 equivalents of the alcohol), leading to the formation of the most substituted ether. 

Included among the many types of vinyl monomers that have been subjected to photoinitiated cationic polymerization are styrene," substituted styrenes, a-methylstyrenes, N-vinylcarbazole, alkyl vinyl ethers, prop-l-en-l-yl ethers, ketene acetals, and alkoxyallenes. Most useful in the crosslinking photopolymerizations employed for UV curing applications are multifunctional vinyl ethers and multifunctional prop-l-en-l-yl ethers. A number of multifunctional vinyl ether monomers are available from commercial sources, while multifunctional prop-l-en-l-yl ethers can be readily prepared by catalytic isomerization from their corresponding allyl ether precursors. The photoinitiated cationic... 

Another example for block copolymer synthesis is the preparation of poly (methylene-fc-styrene), which was achieved by using a hydroxyl-terminated living polystyrene obtained by TEMPO-mediated living radical polymerization [75] (Scheme 55). The chain end hydroxyl group was transformed into an allyl ether moiety, which was subjected to hydroboration with BH3 to afford polystyrene macroinitiator for the polymerization of 11. After chain elongation with 11 oxi-dation of the C-B chain ends furnished poly(methylene- -styrene) bearing TEMPO and hydroxyl group at chain ends. 

Allyl groups are subject to oxidative deprotection with Chromiapillared Montmorillonite Clay, -BuOOH, CH2CI2, isooctane, 85% yield. Allylamines are cleaved in 84—90% yield, and allyl phenyl ethers are cleaved in 80% yield. 

The outcomes of intramolecular cyclizations of hydroxy vinylepoxides in more complicated systems can be difficult to predict. In a study of the synthesis of the JKLM ring fragment of dguatoxin, epoxide 44 was prepared and subjected to acid-mediated cydization conditions (Scheme 9.24) [114]. Somewhat surprisingly, the expected oxepane 45 was not formed, but instead a mixture of tetrahydropyran 46 and tetrahydrofuran 47 was obtained, both compounds products of attack of the C6 and C5 benzyl ether oxygens, respectively, on the allylic oxirane position (C3). Repetition of the reaction with dimsylpotassium gave a low yield of the desired 45 along with considerable amounts of tetrahydropyran 48. 

Addition of allylic zinc bromides to nitrones, generated in situ from allylbro-mides and zinc powder in THF (670), allyltributylstannane (671) and lithiated allyl ferf-butyldimethylsilyl ether (672), proceeds regioselectively in good yields and is used to synthesize homoallyl hydroxylamines (Scheme 2.189). The latter were subjected to an iodo cyclization reaction (see Scheme 2.186). 

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