Retention entries

Reaction with nucleophiles is difficult (entries 8 and 9), and proceeds with retention in each case this is consistent with the known behavior of the Fe(CC 2(Cp) unit as a good nucleophile and a poor leaving group (147). Electrophilic attack by chlorine also involves retention (entry 10). 

Electrophilic attack by Cl2 causes cleavage with retention (entry 20) a number of other compounds either do not react (e.g., alkyl, aryl,... 

Protonation with Bronsted acids proceeds with retention (Table 9). Alkylation, silylation, stannylation, carbon dioxide, and carbon disulfide addition (entries 3-10,12,25) are accompanied by inversion. This is also true for the reaction with acid chlorides (entry 13), but esters react with clean retention (entries 14-16). Aliphatic aldehydes and ketones add to the Hthium compound 216a with complete retention of configuration. A notable exception was found for benzaldehyde it is added with inversion (entry 23). 

Section A of Scheme 10.15 contains a number of examples of Curtius rearrangements. Entry 1 is an example carried out in a nonnucleophilic solvent, permitting isolation of the isocyanate. Entries 2 and 3 involve isolation of the amine after hydrolysis of the isocyanate. In Entry 2, the dihydrazide intermediate is isolated as a solid and diazotized in aqueous solution, from which the amine is isolated as the dihydrochloride. Entry 3 is an example of the mixed anhydride procedure (see p. 948). The first stage of the reaction is carried out in acetone and the thermolysis of the acyl azide is done in refluxing toluene. The crude isocyanate is then hydrolyzed in acidic water. Entry 4 is a reaction that demonstrates the retention of configuration during rearrangement. 

On this basis the porosity and surface composition of a number of silicas and zeolites were varied systematically to maximize retention of the isothizolinone structures. For the sake of clarity, data is represented here for only four silicas (Table 1) and three zeolites (Table 2). Silicas 1 and 3 differ in their pore dimensions, these being ca. 20 A and 180 A respectively. Silicas 2 and 4, their counterparts, have been calcined to optimise the number and distribution of isolated silanol sites. Zeolites 1 and 2 are the Na- and H- forms of zeolite-Y respectively. Zeolite 3 is the H-Y zeolite after subjecting to steam calcination, thereby substantially increasing the proportion of Si Al in the structure. The minimum pore dimensions of these materials were around 15 A, selected on the basis that energy-minimized structures obtained by molecular modelling predict the widest dimension of the bulkiest biocide (OIT) to be ca. 13 A, thereby allowing entry to the pore network. 

This retention of reagents by the graphite support has been shown in a series of experiments involving volatile dienes such as 2,3-dimethylbutadiene (12) and iso-prene (13) (Tab. 7.2) [30, 31]. The reaction of 12 with diethyl mesoxalate gave 14 in 75% yield after SMW irradiation at low power (30 W) for 20 x 1 min only (Tab. 7.2, entry 1). When conventional heating was used a satisfactory yield was obtained after 4 h at 135 °C in a sealed tube [32]. Ethyl glyoxylate is a weaker carbonyl dienophile... 

The retentive power of graphite towards adipic acid and the catalytic effect of the magnetite, especially present in A, are obvious. TEM examinations of a graphite A sample before and after reaction showed that crystallites of Fe304 appeared to be smaller after the reaction. However, the same graphite sample was reused for three successive reactions without significant loss in yield. When applied to the synthesis of other cyclic ketones (Scheme 7.14), less volatile than 74, it was observed that pressure had an effect on the recovery of product (Tab. 7.9, entries 3 and 4). A slightly reduced pressure (300 mm Hg) was necessary to obtain 3-methylcyclopentanone (75) or cyclohexanone (76) in convenient yield (Tab. 7.9, entries 4 and 5). For the cycliza-tion of suberic acid (73), a less favorable structure, the yield in cycloheptanone (77) remained low (Tab. 7.9, entry 6). 

In an earlier investigation using borane-stabilized chiral menthyl phenyl(hydrogen)phosphonites, arylation with complete retention of configuration at phosphorus could be attained (depending on the solvent used), using o-iodoanisole mediated with tetrakis(triphe-nylphosphino)palladium in catalytic amount (Equation 3.11).187 This approach provides a convenient entry to chiral phosphonites. 

Extracted Ion Chromatogram A chromatogram created by plotting the intensity of the signal observed at a chosen m/z value or series of values in a series of mass spectra recorded as a function of retention time. See also related entry on total ion current chromatogram. 

For reasons discussed above, we needed a complementary, ancillary tool for comparison of the mass spectra of components from multiple urine samples. We desired that the procedure have several characteristics (1) requires little if any manual data entry by the operator (2) utilizes data automatically generated by ChemStation and organized into Microsoft Excel spreadsheets (3) displays both retention times and mass spectral data in the same window (4) minimizes subjective operator judgments and (5) is simple and rapid to use. What emerged after several iterative improvements are the FindPeak macros discussed below. These are largely due to the expertise of Y. Aubut, with valuable input from J. Eggert. 

In addition to the foregoing explanation of retention of configuration, two possibilities may be taken into account. The first is that apical entry is followed by basal departure, and vice versa. Second, the sulfurane intermediate formed may have the structure of a square basal pyramid. In both cases nucleophilic substitution reactions may occur with retention of configuration without ligand reorganization. It appears that the apicophilicity of substituents in sulfurane species... 

As early as in 1973 it was shown [1089] that the C-H insertion of acceptor-substituted carbene complexes can take place with retention of configuration (e.g. Table 4.5, Entry 3) [953,1090,1091]. In the case of intramolecular C-H insertions into methylene groups high diastereoselectivities are often observed when 4-6-membered rings are formed (see examples in Tables 4.4-4.S). 

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