Metalation reaction, with benzaldehyde

Influence of Metal Center on Kinetic Aldol Reactions with Benzaldehyde... 

The chemical reactivities of such titanium homoenolates are similar to those of ordinary titanium alkyls (Scheme 2). Oxidation of the metal-carbon bond with bromine or oxygen occurs readily. Transmetalations with other metal halides such as SnCl4, SbClj, TeCl4, and NbCls proceed cleanly. Reaction with benzaldehyde gives a 4-chloroester as the result of carbon-carbon bond formation followed by chlorination [9]. Acetone forms an addition complex. No reaction takes place with acid chloride and tm-alkyl chlorides. 

The nature of the substituents located at the 2-, 4-, and 6-positions of 1,3-dise-lenanes favors either C-Se bond cleavage or a-deprotonation. For = H, Me, Ph, in the 2-position, the action of n-BuLi, PhLi or MeLi afforded C-Se cleavage with formation of j8-hydroxyalkyl-(3-butylselanylpropyl)selenides (60-85%) after reaction with benzaldehyde or acetone [16] (Scheme 17, reaction 1). With two methyl groups in cfs-4,6-positions, the metalation by an alkyllithium is strongly dependent on the nature of the C-2 substituent. From a czs-C-2-methyl-substituted derivative, metalation requires the use of s-BuLi, no reaction being observed with n-BuLi or t-BuLi (Scheme 17, reaction 2). For cis- or trans-2-phenyl-l,3-disele-nane, metalation can be performed with MeLi or PhLi and an unexpected C-Se... 

Electrophilic substitution is difficult with electron-deficient heteroatomic compounds such as pyridine and quinoline. However, an electrophile can be readily introduced when the heterocycles have an effective ortho-directing group such as a sulfamoyl moiety. Lithiation of the 2-pyridinesulfonamide (51) was performed at low temperature by using 2 equivalents of LDA in ether at —78 °C for 1.5 h (equation 27). Addition of benzophenone to the solution of 52 gave the adduct in high yield38. Metallation of the 4-pyr-idinesulfonamide 53 with 3 equivalents of LDA, followed by reaction with benzaldehyde, afforded the 3,5-disubstituted pyridine 54 (equation 28). 

The preparation of substituted diaryl-ethenes, stilbenes, and analogues (e.g., stilbazoles) has been achieved by Wittig [45] or Homer-Emmons reactions [46] of substituted benzaldehydes and benzyl-triphenylphosphonium halides or benzyl-diethoxyphosphonates (see Scheme 4). 4-Methylpicolinium salts [96a,b] or 4-meth-ylpicoline-A-oxides [96c], upon reaction with benzaldehydes under basic conditions lead directly to the corresponding stilbazo-lium salts or stilbazole-TZ-oxides, respectively. As of late, the metal-catalysed cross-... 

The work of Hyatt on cyclotriveratrylene—derived octopus molecules contrasts with this. Of course, these species have the advantage of ligand directionality absent in the benzene-derived octopus molecules. Except for the shortest-armed of the species (i.e., n = 1), all of the complexing agents (i.e., n = 2—4) were capable of complexing alkali metal cations. Synthesis of these species was accomplished as indicated below in Eq. (7.7). These variations of the original octopus molecules were also shown to catalyze the reaction between benzyl chloride and potassium acetate in acetonitrile solution and to effect the Wittig reaction between benzaldehyde and benzyltriphenylphos-phonium chloride. 

Durst and coworkers were the first to report the condensation of chiral a-sulphinyl carbanions with carbonyl compounds477. They found that metallation of ( + )-(S)-benzyl methyl sulphoxide 397 followed by quenching with acetone gives a mixture of dia-stereoisomeric /i-hydroxy sulphoxides 398 in a 15 1 ratio (equation 233). The synthesis of optically active oxiranes was based on this reaction (equation 234). In this context, it is interesting to point out that condensation of benzyl phenyl sulphoxide with benzaldehyde gave a mixture of four / -sulphinyl alcohols (40% overall yield), the ratio of which after immediate work-up was 41 19 8 32478. 

Another SBU with open metal sites is the tri-p-oxo carboxylate cluster (see Section 4.2.2 and Figure 4.2). The tri-p-oxo Fe " clusters in MIL-100 are able to catalyze Friedel-Crafts benzylation reactions [44]. The tri-p-oxo Cr " clusters of MIL-101 are active for the cyanosilylation of benzaldehyde. This reaction is a popular test reaction in the MOF Hterature as a probe for catalytic activity an example has already been given above for [Cu3(BTC)2] [15]. In fact, the very first demonstration of the catalytic potential of MOFs had aheady been given in 1994 for a two-dimensional Cd bipyridine lattice that catalyzes the cyanosilylation of aldehydes [56]. A continuation of this work in 2004 for reactions with imines showed that the hydrophobic surroundings of the framework enhance the reaction in comparison with homogeneous Cd(pyridine) complexes [57]. The activity of MIL-lOl(Cr) is much higher than that of the Cd lattices, but in subsequent reaction rans the activity decreases [58]. A MOF with two different types of open Mn sites with pores of 7 and 10 A catalyzes the cyanosilylation of aromatic aldehydes and ketones with a remarkable reactant shape selectivity. This MOF also catalyzes the more demanding Mukaiyama-aldol reaction [59]. 

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