Allylation reaction alkoxy

The analysis of open transition states in the chelate-controlled allylation reactions of a- and ff-alkoxy aldehydes with Type II allylmetal reagents is much simpler (Fig. 11-5). In these cases, only the synclinal transition state 21 and the antiperiplanar transition state 22 are considered as viable possibilities. Other possible transition states have been eliminated because of the perceived requirement that... 

In their synthesis of olivin, the aglycon segment of olivomycin A, Roush and coworkers used a highly diastereoselective substrate-directed y-alkoxy allylation reaction to set the C(l ) stereocenter [80]. Thus, reaction of the aldehyde 90, derived from L-threonine, with the [(Z)-y-methoxyallyl]boronate 91 resulted in the highly diastereoselective formation of adduct 92. The stereochemistry of 92 is consistent... 

Although silyloxy groups do not participate in chelates under most conditions, Evans and co-workers have recently reported that the terr-butyldimethylsilyl-pro-tected / -alkoxy aldehyde 102 undergoes highly diastereoselective chelate-con-trolled allylation reactions with allyl and /J-methyl allyltri- -butylstannanes 98 using Me2AlCl (2.5 equiv) as the Lewis acid promoter (Eq. (11.2)) [89]. 

In the reactions of Type II allylmetal reagents with chiral aldehydes, y -alkoxy substituents on the aldehyde can exert a strong influence on the reaction, much more so than in reactions of Type I allylmetal reagents. Reetz and co-workers reported that the BF3-OEt2-catalyzed allylation reaction of the /f-benzyloxy aldehyde 130 with allyltrimethylsilane 131 is selective for the, 3-anti diol 132 (Eq. (11.7)) [92]. Evans and co-workers sub.sequently rationalized this result by invoking tran-... 

In the Type II allylation reactions of a-methyl-/i-alkoxy aldehydes, the principles of 1,2- and 1,3-asymmetric induction both contribute to the reaetion diastereo-selectivity. Evans and co-workers have explained the stereoehemical outcome of these reactions in terms of a merged 1,2- and 1,3-asymmetric induction model [931- For example, the 2,3-anti aldehyde 135 reacts with allyl- and methallyltri-n-butylstannanes 98, generating the Felkin homoallylic alcohols 136 with >99 1 diastereoselectivity (Eq. (11.8)) [93]. 

The diastereoselectivity of these reactions is consistent with product formation occurring through transition state 137, where the reactive conformation of the aldehyde in the transition state (corresponding to the normal Felkin-Anh model) minimizes steric interactions with the allylstannane as well as the 1,3-dipole interactions of the aldehyde and the /(-alkoxy group. The allylation reaction of the 2,3-syn aldehyde 138, however, with allyltri-n-butylstannanes 98, generates the anti-Felkin adducts 139 preferentially (Eq. (11.9)) [93], The stereochemistry of these reactions is consistent with product formation occurring preferentially through transition state 140, in which 1,3-dipole interactions of the aldehyde and the P-... 

Allylations of -alkoxy esters were demonstrated under atom and group transfer conditions using allylsilanes and chelating Lewis acid conditions [28]. Equation (13.18) illustrates the basic mechanism for this reaction. Once again, selectivities greater than 100 1 favoring the anti product and yields of 87% are reported. Results from this study suggest that inclusion of Lewis acids may help facilitate the atom transfer step. 

Allylation reactions can be designed to effect high stereoselectivity in the case of chiral /3-alkoxy aldehydes, in which the ether oxygen provides for effective coordination with a Lewis acid. Multi-valent, oxophilic Lewis acids serve to pre-organize the aldehyde substrate in a six-membered chelation complex. As in the examples of a-chelation control, an open transition state is deployed with synchnal or antiperiplanar orientations based upon the consideration of steric interactions with placement of the small (hydrogen) vinyl substituent of the allylic stannane over the preformed metallocycle. Several examples are illustrated in Scheme 5.2.20. i... 

Scheme 5.2.60 Stereocontrol in the allylation reactions of y-(alkoxy)allylstannanes...

The presence of the second allylic functionality (alkoxy moiety) apparently did not interfere in the reaction pathway. However, when the diethylamino group was replaced by an imido (or an amido) function, i.e., 71, a move in the direction of the 0-function to give 72 occurred, Eq. (14). 

Similar electrophilic activation of coordinated peroxides or alkylperoxides can be observed for the metal ions in intermediate oxidation states. To give just one example, Sharpless epoxidation takes advantage of an electrophilic activation of alkyl hydroperoxides at titanium(IV). Notably, efficient epoxidation requires substrate binding in the vicinity of coordinated alkylperoxide, thus limiting the substrate scope of this reaction to allylic alcohols (alkoxy group acts as an anchor).1,45... 

The double bond isomerization of olefins can be performed at very low temperature, for example at 80 °C (339,388), but the alumina needs to be outgassed at temperatures above 300 °C prior to the catalytic reaction. This pretreatment implies that the surface is partly dehydrated and contains active cation—anion pairs. Infrared spectra clearly showed the formation of aUyl species at room temperature on partially dehydrated Y-AI2O3 (351), whereas recent C NMR spectroscopic investigations surest that both allylic and alkoxy species are formed from propene and butenes on Y-AI2O3 (389). 

The extent to which cooperation between the a-oxygen atom and conuxil of n-facial nucleophilic attack reaches a maximum (>97 3) is when the system has been rigidified conformationally and the 2-methoxy and 4-rm-butyl substituents are both equatorially oriented. Since allylation reactions performed with indium under aqueous conditions are generally far more stereoselective toward a-alkoxy cyclohexanones than are other organometallics under anhydrous conditions, this chemistry merits consideration as a synthetically useful operation. 

The combined carbocupration of ynol ether followed by a zinc homologation in the presence of aldehydes has provided, in a single-pot operation, stereodefined allylic vicinal diol substmctures in good isolated yields and stereoselectivities (up to 92 8 dr) The stereochemistry of the final adducts suggests that the reaction 0 proceeds through a chairlike transition state in which the substituent of the aldehyde preferentially occupies a pseudoaxial position to avoid gauche interactions with an -configurated alkoxy-substituted aUylmetal species. A similar stereochemical outcome has been reported for the allylation reaction of 3,3-disubstituted allylzinc species with aldehydes. ... 

In a formally similar reaction, the 4-methanesulfonyl-/3-lactam (95) undergoes displacement of methanesulfinate on treatment with propargylic or allylic alcohols in the presence of a Lewis acid catalyst to give a mixture of the cis- and tr<2Ms-4-alkoxy-/3-lactams (96) and (97) (79JCS(P1)2268). 

Thiazole, 2-acetylamino-4-methyl-alkylation, 6, 256 Thiazole, 2-acylamino-4-hydroxy-synthesis, 6, 297 Thiazole, 5-alkoxy-cleavage, 6, 289 synthesis, 6, 302 Thiazole, 2-alkyl-A7-alkylation, 6, 253 hydrogen exchange, 6, 276 methylation, 6, 253 quatemization, 6, 253-254 reactions, S, 88 Thiazole, 4-alkyl-A7-alkylation, 6, 253 methylation, 6, 253 quatemization, 6, 253-254 Thiazole, 5-alkyl-A7-alkylation, 6, 253 methylation, 6, 253 Thiazole, 2-alkylamino-tautomerism, 6, 248 Thiazole, 4-alkyl-2,5-dimethyl-quatemization, 6, 253-254 Thiazole, 2-alkylthio-reactions, S, 103 rearrangement, 5, 103 6, 291 Thiazole, 3-allyl-4-hydroxy-2-imino-synthesis, 6, 297 Thiazole, 2-allyloxy-rearrangement, 6, 289 Thiazole, 2-amino-diazo coupling, 6, 257 nitration, 6, 255... 

Further reactions of allyl organometallics with a-alkoxyaldimines 1, prepared from (S)-2-(methoxymcthoxy)propionaldehyde and (R)- and (S)-l-phenylethylamine, illuminate the difference in the influence of the nitrogen chiral auxiliary and the x-alkoxy center7. 

As the results show, the chirality of the a-alkoxy center, as well as the type of allyl metal employed, are the two most important determinants for the stereochemical outcome of the reaction. In other words, the 1,2-asymmetric induction combined with the right choice of the allyl organometallic overrides the influence of the chiral nitrogen substituent. 

Molybdenum, tris(phenylenedithio)-structure, 1,63 Molybdenum alkoxides physical properties, 2,346 synthesis, 2,339 Molybdenum blue liquid-liquid extraction, 1,548 Molybdenum cofactor, 6,657 Molybdenum complexes acrylonitrile, 2,263 alkoxides, 3,1307 alkoxy carbonyl reactions, 2,355 alkyl, 3,1307 alkyl alkoxy reactions, 2,358 alkyl peroxides oxidation catalyses, 6,342 allyl, 3,1306... 

Kwiatek and Seyler were the first to report that many organopenta-cyanides, when treated first with acid and then with alkali, liberate nitriles 110). This reaction occurs with unsubstituted primary and secondary alkyl, benzyl, vinyl, and phenyl complexes, while allyl, 2-oxo-, 2-hydroxy-, and 2-alkoxy complexes simply release the organo-ligand on treatment with acid, and 1-cyanoalkyl and a-pyridyl complexes are stable 105) (see also Table IV). The yield of nitrile is usually far from quantitative and is... 

Nucleophilic addition to a, -unsaturated sulfones has long been known. For example, treatment of divinyl sulfone with sodium hydroxide has been known to afford bis( -hydroxyethyl) sulfone "", while the reaction of a- and -naphthyl allyl sulfones and allyl benzyl sulfone " with alkali hydroxide or alkoxide gave -hydroxy or alkoxy derivatives. In the latter reaction, the allyl group underwent prototropy to the 1-propenyl group, which in a subsequent step underwent nucleophilic attack . Amines, alcohols and sulfides are known to add readily to a, -unsaturated sulfones, and these addition reactions have been studied widely. In this section, the addition of carbon nucleophiles to a, ji-unsaturated sulfones and the reactions of the resulting a-sulfonyl carbanions will be examined. 

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