Standard precursor synthesis

In standard csd processing the aim is to produce dense polycrystalline, columnar or even epitaxial thin films. The above described csd precursor solution did not lead to satisfactory dense PbTi03 thin films. Nevertheless, the opposite of dense films, i.e. separated nanostructures are of great interest for studying intrinsic size effects. For this reason the before introduced PbTi03 precursor synthesis was modified. The flow chart in Figure 18.7 displays the main modifications of the basic csd route. 

The Pd-catalyzed carbonylation of aryl halides (cf Section 2.1.2) occurs with high turnover numbers and reaction rates in SCCO2 as the solvent using standard precursor complexes and commercially available phosphine or phosphite ligands [30]. The generally better performance of the phosphite-based catalysts was attributed to their better solubility in the reaction mixture, but the formation of Pd carbonyl complexes was also mentioned as a possibility. The [Ni(cod)2]/dppb system (dppb = l,4-bis(diphenylphosphino)butane) was investigated in an early study as a catalyst for the synthesis of pyrones from alkynes and CO2 under conditions beyond the critical data of carbon dioxide [31]. Replacing dppb with PMcs results in a system with better solubility and catalytic performance, albeit catalyst deactivation remains a problem [3 c, 15]. 

F-FLT is prepared by nucleophilic reaction between 18F-sodium fluoride and a precursor, 2,3 -anhydro-5,-0-benzoyl-2 -deoxylhymidine, which is prepared by standard organic synthesis (Machula et al, 2000). 18F-sodium fluoride is added to a mixture of Kryptofix 2.2.2 and potassium carbonate in acetonitrile, and the mixture is dried to a residue by heating at 120°C for 5 min. The precursor in dimethyl sulfoxide (DMSO) is added to the dried residue and heated at 160°C for 10 min. Hydrolysis of the 5 -0-protecling... 

The derivatives of the aminophenols have important uses both in the photographic and the pharmaceutical industries. They are also extensively employed as precursors and intermediates in the synthesis of more compHcated molecules, especially those used in the staining and dye industry. All of the major classes of dyes have representatives that incorporate substituted aminophenols these compounds produced commercially as dye intermediates have been reviewed (157). Details of the more commonly encountered derivatives of the aminophenols can be found in standard organic chemistry texts (25,158). A few examples, which have specific uses or are manufactured in large quantities, are discussed in detail in the following (see Table 6). 

When [ H]-labeled precursors are employed the resulting compounds can be used as internal standards for analysis, especially by utilization of mass spectrometric methods. Appropriate deuterated standards are shown in Fig. 7. The introduction of deuterium into the A9-THC precursors can be done with Grignard reagents such as C[ H3]MgI or reducing substances such as LiAl[ H4]. The general procedures for the synthesis with these [ Hj-labeled precursors are the same as described above for the unlabeled compounds [76,78]. 

The acidic conditions of standard SBA-15 synthesis [35] cause the precipitation of metal nanoparticles without silica encapsulation, or the formation of amorphous silica due to the presence of the polymer used for nanoparticle synthesis. Therefore, the SBA-15 framework was synthesized under neutral condition using sodium fluoride as a hydrolysis catalyst and tetramethylorthosilicate (TMOS) as the silica precursor. Pt particles with different sizes were dispersed in the aqueous template polymer solution sodium fluoride and TMOS were added to the reaction mixture. The slurry aged at 313 K for a day, followed by an additional day at 373 K. Pt(X)/SBA-15-NE (X = 1.7, 2.9, 3.6, and 7.1nm) catalysts were obtained by ex-situ calcination (see Section 3.2). TEM images of the ordered... 

Scheme 2. Encapsulation of size- and shape-controlled Pt nanoparticles under neutral hydrothermal synthesis conditions of SBA-15. Silica templating block copolymers and silica precursors were added to PVP-protected Pt nanoparticle solutions and subjected to the standard SBA-15 silica synthesis conditions. Neutral, rather than acidic pH conditions were employed to prevent particle aggregation and amorphous silica formation [16j. (Reprinted from Ref. [16], 2006, with permission from American Chemical Society.)...

The second example involves the synthesis of ortho-dipropynylated arenes (Scheme 4.12b), which serve as precursors to tribenzocyclyne by way of an alkyne metathesis reaction (see also Scheme 6.31). Here, a Sonogashira reaction was carried out in a pre-pressurized (propyne at ca. 2.5 bar) sealed microwave vessel in a standard single-mode microwave reactor. Double-Sonogashira coupling of the dibromodiiodo-benzene was completed within 20 min at 110 °C [30]. 

However, this multistep procedure is experimentally complex. A simpler variation described in 199127 consists of the reaction of an aldehyde and a nitro compound in the presence of triethylamine, TBAF and tert-butyl-dimethylsilyl chloride. Under these conditions, nitro sugars are obtained in good yieds and higher diastereoselectivities than those afforded by the standard conditions. This procedure was used in several synthesis of 2-nitro-2-deoxyaldoses, as for the condensation of l,l-diethoxy-2-nitroethane and l,2 3,4-di-0-isopropylidene-a-D-galacto-hexodialdo-l,5-piranose.28 More recently, it was applied to the addition of ethyl nitroacetate to the D-glucose derived aldehyde 18, to give nitro sugar derivatives 26, key precursors of polysubstituted cyclohexane a-amino acids (Scheme 10).29... 

The same group proposed also a general route to carbocycles of type 49.31 Starting from D-glucose, the precursor 46 was prepared in a few standard steps it could be used either for the synthesis of imino sugars or carbocycles... 

In general, sulfur-substituted allenes are accessible starting from alkyne precursors by a variety of transformations such as isomerization, rearrangement or addition reactions. The standard method for the synthesis of donor-substituted allenes is again the base-induced isomerization of alkynes. This very first method was applied for the preparation of achiral [11, 162, 163] and chiral [164] S-functionalized 1,2-dienes (Scheme 8.78). 

---