Lewis, Nate

The reaction of CF3I and CgFjI with dialkylzmc in the presence of a Lewis base, such as diglyme or pyridine, quantitatively gives the corresponding fluori-nated organozinc complexes [32] (equation 23) When Rf is C2F5 or iso CjF-j, the pure zinc complexes are not isolated... 

Moreover, these experiments reveal some unique properties of the chlorostan-nate ionic liquids. In contrast to other known ionic liquids, the chlorostannate system combine a certain Lewis acidity with high compatibility to functional groups. The first resulted, in the hydroformylation of 1-octene, in the activation of (PPli3)2PtCl2 by a Lewis acid-base reaction with the acidic ionic liquid medium. The high compatibility to functional groups was demonstrated by the catalytic reaction in the presence of CO and hydroformylation products. 

As has been described for allyl bromide (see preceding paragraph), allyl sulfides and allyl phenyl selenide react with 6-diazopenicillanates 134 under Cu(acac)2 catalysis to give the products of ylide formation and subsequent [2,3] rearrangement 155-159). Both C-6 epimers are formed. The yields are better than with BF3 Et20 catalysis, and, in contrast to the Lewis acid case, no 6[Pg.139]

Obviously, the basic site in KB5H8 is its basal B-B single bond and, therefore, reactions with Lewis acids are to be expected. A typical example is the reaction with diborane in ether at —78 °C which generates via its //-adduct (3c2e-BBB bond) the nido-undeca-hexaborate(l—), B6Hn, by cluster expansion. This anion can be proto nated to B Hn [53],... 

Guo et al. prepared N-(3-chloro-4-fluorophenyl)aminomethylenemalo-nate (256, R = 3-C1, R1 = 4-F, R2 = R3 = Et) in 60-70% yields when 3-chloro-4-fluoroaniline was reacted with triethyl orthoformate and diethyl malonate in the presence of a Lewis acid. From the reaction mixture, ethyl A-(3-chloro-4-fluorophenyl)-2-[(3-chloro-4-fluorophenyl)-aminomethylene]malonamate and A-(3-chloro-4-fluorophenyl)formanilide were also isolated as byproducts (88MI3). 

The intermediate cation is subsequently deproto-nated to yield the acylated product. However, this acyl derivative is actually a ketone, which can also complex with the Lewis acid. Accordingly, the final... 

Note If you would like to see the hard numbers on the global energy perspective presented in a cogent, concise manner we strongly suggest to all a web-broadcast talk by Professor Nate Lewis of Caltech at http //nsl.caltech.edu/energy.html... 

Moreover, these experiments reveal some unique properties of the chlorostan-nate ionic Hquids. In contrast to other known ionic Hquids, the chlorostarmate system combine a certain Lewis acidity with high compatibiHty to functional groups. 

Lewis acid complexes of alkyl halides and alkyl sulfonates (Figure 5.26, left) and proto-nated alcohols (Figure 5.26, middle) are additional reactive electrophiles in Friedel-Crafts alkylations. The aromatic compound displaces their respective leaving group in an SN2 process. This is in principle possible (Section 2.4.4) for primary or secondary alkylating agents and alcohols. 

Prof. Nate Lewis website http //nsl.caltech.edu/energy.html. 

Many treatments of these solvent systems are in terms of acid-base equilibria, and the basis is to regard Cl as a Lewis base. In these terms, the heptachloroalumi-nate is a strong Lewis acid. 

Holstein, S.A., Cermak, D.M., Wiemer, D.F., Lewis, K., and Hohl, R.J. (1998). Phospho-nate and bisphosphonate analognes of farnesyl pyrophosphate as potential inhibitors of farnesyl protein transferase. Bioorg Med Chem 6 687-694. 

The proposed exo transition state (for cyclopentadiene) is illustrated in Fig. 4, and shows that one of the -NCH2Ar groups blocks the lower face of the j-tran.v-coordi-nated dienophile [25]. The authors proposed s-trans geometry for the complex a-sub-stituted unsaturated aldehyde/Lewis acid, in contrast with to previous observations that this aldehyde reacts in the s-cis form [17]. 

Chelation with copper(ll) Lewis acids has been used to change the reactivity of bis ketenes toward alcohols. The alcoholysis of 52 in the presence of copper acetylaceto-nate derivatives afforded the cyclic lactones 54 (Sch. 14) [35]. The addition of alcohols to 52 without the Lewis acid led to the formation of ketene esters 53 which would not undergo cyclization upon treatment with the copper(ll) complexes. It is suggested that chelation of the bis-ketene in a jr-fashion accounts for the lactone products. Although chiral Lewis acids were used, the products were obtained as racemates probably because of very facile epimerization. 

The use of catalyst 187 or 188 (see Sch. 43) in cycloadditions requires anhydrous conditions. Recently, several practical alternatives for this requirement have been reported. Evans has shown that the easily manipulated aquo complex prepared from 187 and water can be dehydrated to the active catalyst in the reaction vessel by addition of molecular sieves, without any loss of reactivity or selectivity [87]. Copper(II) perchlorate is available commercially as a hexahydrate. Ghosh and co-workers have reported that a complex 207 prepared from an aminoindanol-derived bisoxazoline and Cu(C104)2 6H2O is an excellent Lewis acid in Diels-Alder reactions (Sch. 46). It is interesting to note that the generally sluggish reactions with oxazolidinone croto-nates proceed with very high selectivity at room temperature [88]. 

Infrared techniques are used to study the nature of the OH groups present on rare earth forms of Y zeolite. The infrared spectra of pyridine adsorbed on REY, after calcination at a series of temperatures, show that Bronsted and Lewis acidities are present. ESR techniques are used to measure the number of anthracene radical ions which can be formed on the REY zeolite. Electron transfer occurs at the tricoordi-nated aluminum atoms in the case of LaY zeolite, while for Ce Y, the centers have been identified as Ce ions. 

---