SiCl treatment

This can be related to the fact that the Si atoms substituting Al in the framework during the SiCl treatment originate outside the zeolite (i.e. from SiCl,), while in the steam/ acid treatment the corresponding silicon atoms originate in other parts of the zeolite crystals. This can also explain the absence of "secondary" pores in the material prepared with SiCl, as shown by sorption isotherms for different hydrocarbons (27). 

Ester Enolate Aldol Additions to Aldehydes. Among the first examples of aldol additions employing chiral Lewis bases as catalysts were the additions of trichlorosilyl ketene acetals to aldehydes. Silyl ketene acetal 7 could be generated by metathesis of methyl tributylstannylacetate with SiCL. Treatment of 7 with benzaldehyde and 10 mol % of a phosphoramide in CH2CI2 at —78°C afforded aldol products in good to high yields with moderate enantioselectivities for all phosphoramides employed. Reaction of 7 with pivalaldehyde provided aldol products in similar yields and with slightly improved enantioselectivities. The increase in stereoselection is presumably attributed to a less com-... 

Anotlier important modification metliod is tire passivation of tire external crystallite surface, which may improve perfonnance in shape selective catalysis (see C2.12.7). Treatment of zeolites witli alkoxysilanes, SiCl or silane, and subsequent hydrolysis or poisoning witli bulky bases, organophosphoms compounds and arylsilanes have been used for tliis purjDose [39]. In some cases, tire improved perfonnance was, however, not related to tire masking of unselective active sites on tire outer surface but ratlier to a narrowing of tire pore diameters due to silica deposits. 

Because the nucleophiles can be introduced at the orr/io-posidon of the nitro group, various heterocycles can be prepared via VNS and related reacdons. Indoles and related compounds are prepared via the VNS reacdon and subsequent cyclizadon. The VNS reaction of nitroarenes followed by cyclizadon v/ithEt- N-Me SiCl gives 1-hydroxyindoles fEq. 9.53. Cyclizadon is Mso catrilyzed on treatment v/ith bases, in which nitroso intermediates are postidated. 

Aluminum-deficient Y zeolites prepared by reacting Y zeolites with SiCl vapors at 500°C also showed an enrichment of the surface in aluminum (44). The X-ray data show a shift of diffraction peaks to higher 20 values, consistent with a more silicious framework (27). However, the X-ray pattern also indicates some structural differences between this material and the one prepared by the steam/acid treatment. 

The mid-infrared spectra of aluminum-deficient Y zeolites prepared by the reaction of Y zeolites with SiCl are similar to those prepared by steam/acid treatment (27). As in the... 

Treatment of isopropenylacetylene with an excess of BuLi or BuLi.TMEDA does not give rise to double deprotonation, but to a slow addition with formation of an adduct With the super basic reagent BuLi.r-BuOK [45,46,52,53] in a mixture of THF and hexane, dimetallation can be accomplished in a short time at low temperatures. The high efficiency of the dimetallation appears from the excellent yield (> 90%) of MejSiCsCC(CH2SiMe3)=CH2 obtained by quenching with h SiCl. Addition of anhydrous lithium bromide converts the dipotassium compound into the dilithio derivative, which can be used for regiospecific functionalizations. 

The first experimental evidence for the existence of a dimetalated silole 56 was obtained by Joo and coworkers from treatment of 1,1-dichlorosilole 55 with sodium in dioxane114. A red solid was isolated from this reaction, which yielded upon addition of electrophiles such as Me2HSiCl or Mc SiCl the corresponding 57. Upon treatment with t-BuCl or Me3SnCl, coupling products 58 were obtained (Scheme 14). 

Figure 14.51 shows four Ireland-Claisen rearrangements that exhibit simple diastereose-lectivity (see Section 11.1.3 for a definition of the term). The substrates are two cis, trans-iso-meric propionic acid esters. The propionic acid esters in Figure 14.51 are derived from achiral allyl alcohols. This is different from the situation in Figure 14.50. However, these esters contain a stereogenic C=C double bond. Both the esters in Figure 14.51 can be converted into their 7 "-enolates with LDA inpureTHF (cf. Figure 13.16). Silylation affords the two T -con-figured O-allyl-O-silyl ketene acetals A and D, respectively. Alternatively, the two esters of Figure 14.51 can be converted into their Z -enolates with LDA in a mixture of THF and DMPU (cf. Figure 13.17). Treatment with rert-BuMe,SiCl then leads to the Z-isomers B and C of the O-allyl-O-silyl ketene acetals A and D, respectively.

NaBr/H20, LiBr on Amberlyst-15 resin, TiCU-LiCl, " SiCL, I2 with a Sml2 catalyst, and Lil on silica gel. Epoxides can be converted directly to 1,2-dichloro compounds by treatment with SOCI2 and pyridine, or with Ph3P and CCl4. These are two-step reactions a halohydrin is formed first and is then converted by the reagents to the dihalide (10-48). As expected, inversion is found at both carbons. Meso epoxides were cleaved enantioselectively with the chiral B-halodiisopinocampheylboranes (see 15-16), where the halogen was Cl, Br, or I. ° Diatomic iodine gives an iodohydrin with a 2,6-bis[2-(o-aminophenoxy) methyl]-4-bromo-l-methoxybenzene catalyst. ... 

The further removal of the other Al atom can then lead to the formation of Si(OH)2 groups as well. While the formation of SiCl groups is quantitative - it corresponds to two per extracted Al atom - that of the very unstable Si(OH)2 defects is not, and only a small amount remains in the structure due to framework reconstruction. This value is ca. 0.2 /u.c. and corresponds to that obtained from the treatment of Na-MOR with phosgene [13]. (Note, that the previously reported value of 1.5/u.c. has to be corrected, as the -92 ppm line was attributed to the sole Si(OH)2 groups [13].)... 

Most of the procedures describing the conversion of halogenoalkylphosphonates into the corresponding phosphonic acids nse McjSiBr neat or Mc SiCl/Nal in MeCN, followed by treatment with MeOH or H2O. The reaction tolerates snbstitnents such as CCl, CH2Br, or CH2I and proceeds smoothly at room temperature, and the yields obtained are quantitative (Scheme 3.92). 

Homologation. 2-Chloro-l-alken-3-ols are obtained from aldehydes on treatment with 1,1,1-trichloroethane in the presence of CrCl2. They are precursors of propargyl alcohols. Conversion of aldehydes to alkenylsilanes with one more carbon is accomplished by the CrCl2-catalyzed reaction with Mel, Mn, and Me SiCl in THF. ... 

Functional group manipulations. Aliphatic TBS ethers are hydrolyzed with a catalytic amount of McjSiCl and 1 equiv of H2O in MeCN. ArOTBS survives such treatment. Me SiCl also catalyzes the selective acetylation of aliphatic alcohols with trimethyl orthoacetate. ... 

Iminium salts. N-Silyl derivatives of secondary amines react with carbonyl compounds afford a-siloxyamines. On further treatment with Me,SiCl, iminium chlorides are obtained. Trimethylsilyl triflate is superior to Me SiCl since it can induce the transformation in the cases of enolizable aldehydes. a-Chloro ethers are more reactive than carbonyl compounds, enabling the preparation of vinylogous Viehe salts. 

---