Allylation polar effects

Hexafluoroacetone and hydrogen peroxide in buffered aqueous solution can epoxidize alkenes and allylic alcohols.101 N, Af-Dialkylpiperidin-4-one salts are also good catalysts for epoxidation.102 The polar effect of the quaternary nitrogen enhances the... 

The present volume comprises 17 chapters, written by 27 authors from 11 countries, and deals with theoretical aspects and structural chemistry of peroxy compounds, with their thermochemistry, O NMR spectra and analysis, extensively with synthesis of cyclic peroxides and with the uses of peroxides in synthesis, and with peroxides in biological systems. Heterocyclic peroxides, containing silicon, germanium, sulfur and phosphorus, as well as transition metal peroxides are treated in several chapters. Special chapters deal with allylic peroxides, advances in the chemistry of dioxiranes and dioxetanes, and chemiluminescence of peroxide and with polar effects of their decomposition. A chapter on anti-malarial and anti-tumor peroxides, a hot topic in recent research of peroxides, closes the book. 

Photoinduced reactions of homolytic addition of bromotrichloromethane C.CI3B1 to allylic derivatives of germanium and tin could be an illustrative example of the potentialities of CIDNP application to study processes where the polarization effects have not been generated at the initiation stage. An earlier proposed46 overall scheme of CChBr addition to the allylic double bond in the R3MCH2CH=CH2 molecule was based on the analysis of the reaction products (Scheme 5). 

In the case of a sterically hindered allylic methoxycarbonyl group, the epoxida-tion of substituted cyclohexenes-1,4-dienes occurs on the opposite side. Further studies on the epoxidation of j3,7-unsaturated cyclohexenecarboxylic acids and esters indicate that the steric and polar effects of the COaMe group result mainly in anh -epoxidation while the carboxyl group in inert solvent exerts a syn directing effect. ... 

We must realize that polar effects are superimposed on effects due to delocalization of the odd electron. Styrene and butadiene, for example, are highly reactive toward any radical since the transition state contains an incipient benzylic or allylic free radical. This high reactivity is modified—enhanced or lowered—by the demands of the particular attacking radical. 

Table IV compares for a series of dienes the yields of 1,2 addition products obtained with Rh(NBD)(dppe)+ as the catalyst precursor under intercalated and homogeneous reaction conditions. The yields of terminal olefins are consistently higher for the intercalated catalyst. The deviation from solution yields are larger when the intercalated catalyst is solvated with methanol than with acetone.0 Methanol swells the interlayers to an average thickness of 12 A, whereas acetone swells the interlayers to w 15 A. Since the more constricted methanol solvated interlayers provide the higher yields of terminal olefins, spacial factors as well as polarization effects induced by the charged silicate sheets may be contributing to the deviations from solution behavior. In this reaction system polarization effects may well be more important than spacial factors in directing hydrogenation transfer because the spacial requirements of the transition states derived from or r 3 allyl intermediates should be very similar.

Among the various carbon-carbon and carbon-hetero atom bond forming reactions promoted or catalyzed by transition metals, allylic substitution via electrophilic n-allyl-complexes is of utmost importance. Studies focused on the synthetic potential of alkyl or aryl substituted ( n3-allyl)Fe(CO)4 1+) complexes have shown that nucleophilic attack by soft carbon and hetero atom nucleophiles preferentially proceeds regioselectively at the less or syn-substituted allyl terminus.4 Additionally, polar effects on the regioselectivity of this reaction caused by electron-withdrawing functionalities (e.g., CO2R, CONR2) have been examined by the... 

The correlations possess 5 values consistent with the differing steric requirements the numerical magnitude of 5 for the more hindered aromatic species is more than that for the allyl bromide. The range of a for the amine substituents is not significant and the polar effect is therefore constant throughout. 

MSN materials functionalized with AEP and a hydrophobic secondary group such as allyl (AL) and mercaptopropyl (MP) showed a great polarity effect in the nitroaldol condensation of 4-hydroxy- and 4-octyloxybenzaldehyde with nitromethane (Scheme 3.37). ... 

AUyhc and benzylic anions are about 59 kj mol (14kcal mol ) more stable than their non-allylic and nonbenzyUc counterparts. There are two reasons for the stabilities of these anions. The first is resonance stabilization and second is the polar effect of the double bond (Scheme 3.6). 

The conversion of several 0-substituted 2-bromo-2-deoxy-D-arabinono-1,4-lactones into 2-C-allyl lactones on treatment with allyltributylstannane has been disclosed. The stereochemistry of the products appeared dependent on the orientation and nature of the O-substituents as well as on polar effects. 

The intermolecular carbon-carbon bond forming reaction involving allylic sulfones has also been considered without mediators. The successful addition of 2-functionalized allyl sulfones to vinylacetate, taking advantage of favorable polar effects, has been performed by Whitham and co-workers (equation (70))... 

For other allylic substitution reaction of CFs-substituted allylic alcohol derivatives, see Okano T, Matsubara H, Kusukawa T, Fujita M. The polar effect on the regiochemis-try of nucleophilic substitution of trifluoromethylated ju-allylpaUadium complex. J. Org. Chem. 2003 676 43-48. 

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