EWIS ACIDS

Write the Lewis structures of each reactant, identify the iTwis acid and the Lewis base, and then write the Lewis structure of the product (a complex) for rhe following I ewis acid-hase reactions ... 

B 1, ewis acid-base reaction CaO is the base and Si02 is... 

I ewis-acid catalysis causes the ketone to attack the slerically more accessible C-3 carbon atom of epoxyaldchyde 9, which leads to compound 10 with inversion of the configuration at this stereogenic center. ... 

The addition of a Lewis acid, thus creating an M - CO and l.ewis acid interaction, also aids in the reduction of CO by hydrogen. Mueuerties describes i1k catalytic hydrogenation of CO in a NaCl/AlClj melt using lr4(CO) [76]. Products were Ci-Cs linear and branched hydrocarbons. Turnover rates were very low. 

The oxyfprn atom of soeialdehyde has two lone pairs of electrons that tt can donate to a l[Pg.81]

Remember that a. ewis acid is a species that accepts an electron... 

Borane is very reactive because the boron atom has only six electrons P its valence shell. In tetrahydrofuran. solution, BII3 accepts an electron pair from a solvent molecule in a I,ewis acid-base reaction to complete Us octet and lorm a stable Bl l -THF complex. 

The theme of C-glycosyl compounds is covered by two chapters on firee radical- and ewis acid-mediated transformations that address die stereoccmtrolled synthesis of carbon ubsdtuents at the anonmic position. 

The presence of metal cations also promotes post-electron-transfer chemistry with the 02-- from the O2 reduction. The results of Fig. 2-8 and Table 2-7 can be rationalized on the basis of a I.ewis acid-base process that promotes disproportionation to metal peroxide and 02- For example, with excess zinc ion relative to O2 in aprotic media... 

PG Sin gle Klee. Red- Hydride Reductions Acid and J..ewis Acid Soft. Acids Free Rad. Rxn Oxidants ... 

In a review of Diels-Alder reactions. Sauer330 notes that no catalysis with Lewis acids has been observed in the case of dienophiles with no polar substituents (CO. CN). IR spectra show that the I. ewis acid forms a complex with the polar group. 

Dienophile Diene Ligand r.ewis acid ee (%> Yield (%) Ref... 

JCycloadditions. The vinyl selenide I undergoes [2+2]cycloaddition with vinyl ketones in the presence of a I-ewis acid, usually SnCU or A1C1V If the reaction is quenched with H20 rather than an amine, acylsilanes are obtained in 37-50% yield. 

Although the reaction with ethylene oxide is quite successful, substituted epoxides often lead to mixtures. In addition to ring opening by the halide ion. isomerization of the epoxide to an isomeric aldehyde or ketone is catalyzed by the l.ewis-acidic species of the Grignard reagent 6.1471. The... 

Diacyl peroxides may also undergo non-radical decomposition via the carboxy inversion process lo form an acylcarbonale (Scheme 3.27)/ The reaction is of greatest importance for diaroyl peroxides with electron withdrawing substituents and for aliphatic diacyl peroxides (36) where R is secondary, tertiary or ben/.yl. The reaction is thought to involve ionic intermediates and is favored in polar solvents and by I,ewis acids.Other heterolytic pathways for peroxide decomposition have been described. ... 

J.ewis acids have a much greater effect on tacticity in polymerization of... 

Give an example of (a) a weak acid that contains oxygen atoms, (b) a weak acid that does not contain oxygen atoms, (c) a neutral molecule that acts as a F.ewis acid, (d) a neutral molecule that acts as a F.ewis base, (e) a weak acid that contains two ioniz-able H atoms, (f) a conjugate acid-base pair, both of which react with HCl to give carbon dioxide gas. 

Scheme 12.9 T,ewis acid-mediated Ferrier-type carhocyclization.

Scheme 12.16 Proposed mechanism of the I.ewis acid-mediated cyclization. Scheme 12.17 Synthetic plan for an aminocyclitol in hygromycin A.

Scheme 23 Cooperative NHCA ewis acid catalysis for the synthesis of y-lactams...

Boron (I II) Lewis Acids, AUl pewis cids, Ga(lll) Lewis Acids, Injff ewis Acids, Si(IV) Lewis Acids, Sn(ll) and [Sn(IV) Lewis Acids, Bismuth(lll) Lewis Acids, Scandium and Yttrium Lewis cids, Lanthanide Lewis Acid, Titanium ewis Acid, Zr(IV) and Hf(IV) Lewis Acids, [Transition Metal Lewis Acids, Cu(l) ano u(ll) Lewis Acids, Ag(l) and Au(l) Lewis Acids, Polymer-supported Metal... 

---