Shielding facial

Aqueous dispersions of fluoropolymers are in general neutral to moderately alkaline, with the exception of certain coatings for metals, which are strongly acidic. Some additives in the aqueous phase of the dispersion may irritate eyes and/or skin. Therefore, it is advisable to use protective garments, goggles, or facial shield. If the liquid comes in contact with skin, the affected spot must be flushed with water immediately. If the liquid comes in contact with the eyes, they must be flushed immediately and medical help provided as soon as possible. 

The stereochemistry of the products and the regioselectivity of the coupling reaction indicates that adsorption of saturated alkyl radicals is relatively unimportant [20]. Carboxylates which are chiral and non-racemic at the a-position totally lose their optical activity in mixed heterocoupling [21, 22]. This racemization indicates either a free radical as intermediate or its fast desorption-adsorption at the anode. These findings are further supported by the decarboxylation of 3 and 4, which both form the same 1 2 1 mixture of transfrans-, cis,trans- and c ,c -coupled dimer, whilst 5-7 show a slight diastereoselectivity [23, 24]. The latter could be due to some adsorption caused by the phenyl group or double bond and/or by a more effective facial shielding of the radicals (see Chapter 3.3). 

Si-face attack 34 fadal selectivity 309 facial shielding 43 FBSM (l-fluorobis(phenylsulfonyl) methane) 865 Ferrier 1215... 

This catalyst induces preferential re facial attack on simple aldehydes, as indicated in Ligure 2.2. The enantioselectivity appears to involve the shielding of the si face by the indole ring through a ir-stacking interaction. 

After patient contact, remove gown, leg and shoe coverings, and gloves in a designated decontamination area. Hands should be washed prior to removal of respiratory and eye protection (i.e., mask/respirator, face shield, and goggles) to minimize potential exposure of mucous membranes. Wash hands again after removal of facial PPE. 

The preference of the distal attack of olefin (ethylene) on nitronate (257) could be attributed to steric hindrances due to the presence of the axial alkoxy substituent at the C-6 atom, which shields the proximal attack. These hindrances are absent in nitronate (256). However, one could suggest that for nitronate (256) adopting a half-chair conformation, the approach of olefin from the side of the C-6 atom is more shielded even if the C-6 atom is unsubstituted because considerably deviates upward from the plane of the C=N bond of the dipole in comparison to the deviation of the C-5 atom in the opposite direction (see Sections 3.3.3 and 3.5.2). It could be worthwhile to combine this approach with a consideration of the facial preference for model nitronates substituted at the C-5 atom also. 

E) configuration. The dipolar cycloaddition of 141 with a silyl nitronate shows a slight increase of facial selectivity over 132 (Eq. 2.9). Because the cycloadducts are converted directly to the corresponding isoxazolines, only the facial selectivity can be determined. It is believed that the cycloaddition proceeds on the Re face of the dipolarophile due to shielding of the Si face by the auxihary. Both chiral auxiliaries can be liberated from the cycloadduct upon reduction with L-Selectride. 

The number of investigations on the enantioselective dipolar cycloaddition of nitronates is still rather limited. In the case of simple alkyl nitronates, the facial selectivity is controlled solely by the steric environment about the two faces of the chiral unit. For example, the reaction of steroid dipolarophile 270 proceeds with the nitronate approaching the Re face of the alkene (Eq. 2.23) (234). The facial selectivity is controlled by the C(19) methyl group, which blocks the Si face of the dipolarophile. Similarly, exposure of 279 to ethyl acrylate at 40 °C for 24 h, provides a single nitroso acetal (Scheme 2.21) (242). The facial selectivity is presumed to arise from steric shielding by the menthol group, however the full stereostructure has not been established. 

The observed change in stereoselectivity can be rationalized by consideration of the conformation of the 2-(arylsulfinyl)-2-cyclopentenone (24) (Fig. 3). The sul-finyl and carbonyl moieties are normally arranged in an anti periplanar orientation (27). The bulky aromatic substituent on the chiral sulfinyl group shields one face of the alkene and thereby controls the facial selectivity of the reaction. In the presence of the Lewis acid the sulfinyl and carbonyl moieties are locked in a syn orientation (28) as a result of chelation between the two moieties and the metal. Thus, the opposite face of the alkene is shielded and (3-addition results in the other diastereoisomer being formed. 

Introduction. One of several auxiliaries that exploit the asymmetry of naturally occurring (-b)-camphor, the 3-(N-(3,5-dimethylphenyl)benzenesulfonamido)bomeol auxiliary has proven significant utility in the jt-facial differentiation of ester enolates and enoate derivatives. The endo orientation of the C(2) and C(3) substituents places the reactive functionality within the concave pocket created by the bomane skeleton as well as the shielding ability of the M-arylbenzenesulfonamide. 

The circular dichroism spectrum of the isomer designated as A-fac-Fe(mphen)32+ is shown in Figure 4. The facial designation is based on the sharp XH NMR signal observed for the resolved complex relative to the broader signal observed for the synthetic mixture of fac and mer isomers. The shielding is analogous for all protons, thus only a small difference is observed. Thus the absolute purity of the facial isomer cannot be assured. 

As previously discussed for organotitanium reagents, the nature of the added Lewis acid influences the geometiy of the reactive conformer. For example, TiCl4 prefers hexacoordinated complexes, and it induces cycloadditions of benzyl ester of IV-acryloylproline 31 through an s-cis chelate whose Si face is not shielded by a chlorine bound to titanium. The opposite facial selectivity is observed under EtAlCl2 catalysis, probably because the s-trans monodentate complex is the reac-... 

To achieve a high degree of facial selectivity in asymmetric cycloaddition, the employment of tt-shielding in combination with a chiral auxiliary has turned out to be an effective strategy [18]. The capability of asymmetric induction was applied to an immobilized system, designed on the basis of jr-shielding. For this purpose... 

Anodic decarboxylation of the 2-carboxy-butyrolactones 76-78 with acetic acid and the coacids 34 and 35 affords the butyrolactones 79-86 in moderate yields and diastereoselectivities up to 94 /o de (Eq. 10). In these cases a conformationally rigid intermediate radical is generated from 76-78. The facial selectivity is increased compared to the radicals from 65 68 as one side is shielded by R and the other by hydrogen. The face selectivity increases slightly from R = /Pr to R = Ph and strongly with R = tBu. 

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