Examples of reagents

Synthetic procedures are available for the preparation of fluoro, chloro, bromo and iodo compounds from the corresponding lithio derivatives. Perchloryl fluoride (FCIO3), N-chlorosuccinimide, bromine and iodine are examples of reagents which can be used to introduce fluorine, chlorine, bromine and iodine, respectively. 

When a positively charged substituent such as the trimethylam-monio group is anywhere on the ring, but most effectively when it is ortho to the leaving group, it can favorably affect the entropy of activation with anionic nucleophiles and accelerate reaction. A recent example of reagent-substituent interaction is the electrophilic substitution of 2-carboxybiphenyl, nitration (non-polar solvent) of which occurs only at the 2 -position and not the 4 -position and has been postulated to be due to the interaction of the nitronium ion with the carboxyl group. 

Another example of reagent-induced asymmetric synthesis is the enantioselective preparation of phosphoramides 6 by addition of dialkylzine reagents to A-diphenylphosphinoylimincs 4 in the presence of the enantiomerically pure 1,2-amino alcohols 5a or 5 b (diethylzinc does not add to A-silyl- or A-phenylimines)12. Phosphoramides 6 (crystalline solids) are obtained in moderate to good yield and good enantioselectivity. The latter can be enhanced by recrystallization. Acidic hydrolysis with dilute 3 M hydrochloric acid/tetrahydrofuran provides the corresponding amines 7 without any racemization. 

The following examples of reagent sequences, which include the reagent Ammonium monovanadate — p-anisidine described in the second part of the book can also be classified as redox reactions. 

An instance of the enantiofacial preference of the reacting partner overwhelming that of the reagent is shown in the case of the reagent s reaction with the tartrate-derived allyl boronates shown. Even in the mismatched case, this example of reagent-based stereocontrol affords a greater than 10 1 selectivity for the syn product (eq ). ... 

For liquids with a high boiling point, or which decompose on heating, distillation under reduced pressure is the usual method of purification. Again it is convenient and effective to use a one-piece distillation apparatus in conjunction with a double manifold for this type of distillation. The procedure is described in more detail in Chapter 11, and some examples of reagents which can be distilled under reduced pressure are given in Table 6.2. 

The simple procedure given below can be used for most solids, other than those which are extremely reactive with even the slightest amount of moisture or air. Examples of reagents which can be weighed by this method are sodium hydride, potassium hydride, lithium metal, lithium... 

There are numerous other cases in the literature that could be used as examples of reagent access limitations. This review is not exhaustive, and those cases cited here serve to establish the point that the limited accessibility of reagents is an important factor in coal chemistry. Clearly it is worthwhile to attempt to improve the accessibility of coals to reagents. Perhaps in this way significant increases in coal reactivity can be obtained. 

The reaction of the (Z)-crotyldiisopinocampheylborane derived from (+-)-a-pinene with aldehydes at -78 °C, followed by oxidative workup, furnishes the corresponding j yn-P-methylhomoallyl alcohols with 99% diastereoselectivity and 95% enantioselectiv-ity. Use of (Z)-crotyldiisopinocampheylborane derived from (-)-a-pinene also produces 5yn-alcohols with 99% diastereoselectivity but with opposite enantioselectivity, an example of reagent control. 

Other examples of reagents of this group are 2-(5-chloro-2-pyridylazo)-5-diethylaminophenol (5-Cl-PADAP) (formula 4.4), 4-(5-bromo-2-pyridylazo)-l,3-... 

Table 17.1. Examples of reagents and buffer additives disturbing sample detection.

Table II presents examples of reagents that involve 0 and N as well as C as the proton-donating element. Only very few compounds from the table such as formic acid (19), ammonia (10), and phenylethyne (22) had been reacted with Cp3 M prior to our study it has been claimed that Cp3Sm only catalyzes the trimeri-zation of phenylethyne.

In the only example of reagent-based induced diastereoselection reported to date for the [2,3] ylide rearrangement, treatment of the bisallylic sulfonium salt 29 with chiral bases results in an observable, but relatively inefficient, stereochemical induction121. 

Table 16.1 lists examples of reagents used for staining of electrophoretograms. 

Additional examples of reagent-based enantioselection involve the enantioselective hydrogen atom abstraction by chiral amine-boryl [37] or silanethiyl radicals... 

Another example of reagent control can be found in the Sharpless epoxidation of 7. With achiral reagents in the absence of a tartrate ligand, there is weak stereoselection. The tartrate-based catalysts control the enantioselectivity, although there is a noticeable difference between the matched and mismatched pairs. 

Figure 16 Examples of reagents for the phosphorylation of hydroxy groups on solid support.

Table 6.1. Examples of reagents with low polarity, high polarity, and intermediate polarity that undergo oxidative addition to transition metal complexes.

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