Reaction inductive

I.3.3.3.3.I.3. Relative Asymmetric Induction Reactions of Chiral Aldehydes with Achiral Allylboron Reagents... 

Single Asymmetric Induction Reactions of Chiral a-Substituted Allylboron... 

Experimental work using a pulse-quench catalytic reactor650 to probe transition between induction reactions and hydrocarbon synthesis on a working H-ZSM-5 catalyst has resulted in the suggestion that stable cyclopentenyl cations are formed during the induction period from small amounts of olefins formed in an induction reaction 647 One study reports a surprising observation, namely, enhanced aromatic formation over the physical mixture of Ga203 and H-ZSM-5 (1 1) (18.2% of benzene and methylbenzenes).651... 

A paper reports the photo-inductive reaction of di- and tri-naphthyl phosphates in the presence of sensitized DCA to afford 1,1-binaphthyl (31). No reaction was observed with mono-1-naphthyl or di- and tri-phenyl phosphate esters.72... 

The inductive parameter, aL, is the same in both the meta and para positions the resonance parameter, aR, is, of course, appreciably different in the two positions the inductive reaction constant is pv This three-parameter equation was employed to calculate reaction types of meta- and para-substituted benzene derivatives. It was shown that free radical processes yielded different values, and a common set of resonance parameters was not possible. The conclusion is, of course, identical to that of van Bekkum and his co-workers (1959). The utility of a unique set of resonance parameters for electrophilic reactions is obscured by the inclusion of both electrophilic side-chain and electrophilic substitution reactions in a single series. 

However, the extrinsic analogy masks a principal difference consisting in the fact that in the case where chemical induction reactions are interrelated, consequently, they may not be described by two independent systems of differential equations, as for parallel reactions. If one makes an attempt to describe them by kinetic reactions for consecutive (or consecutive-parallel) reactions, similar to scheme (3.17), then conjugated reactions will be reduced to consecutive reactions, from which they principally differ. So what are the kinetic expressions that may show the individuality of chemical induction ... 

Thus, taken together, the theoretical and experimental studies carried out lead to a new, chemically particularized mechanism of conjugated dehydrogenation, which consists of the primary (induction) reaction of H202 dissociation and the secondary (inducible) reaction of conjugated dehydrogenation. 

None of the steroid molecules is colored so direct electronic spectrophotometric analyses must be done in the near UV range. The major chromophores are, of course, the aromatic ring, ketone, conjugated ketones, and ethynyl groups. With some exceptions prior derivatization reactions are generally required for the determinations of sterols. These reactions can be either reversible or irreversible. Ketal formation, for instance, is an example of the latter type color induction reactions are examples of the second kind. 

Precursor of Useful Chiral Ligands. OPEN is widely used for the preparation of chiral ligands. Organometallic compounds with these ligands act as useful reagents or catalysts in asymmetric induction reactions such as dihydroxylation of olefins, transfer hydrogenation of ketones and imines, Diels-Alder and aldol reactions, desymmetrization of meso-diols to produce chiral oxazolidinones, epoxidation of simple olefins, benzylic hydroxylation, and borohydride reduction of ketones, imines, and a,p-unsaturated carboxylates. ... 

By analogy with previous results with enol silyl ethers of ketones, non-substituted silyl ketene acetals result in less stereoregulation. Propionate-derived silyl ketene acetals, on the other hand, result in a high level of asymmetric induction. Reactions with aliphatic aldehydes, however, result in slightly reduced optical yield. With phenyl ester-derived silyl ketene acetals, erythro adducts predominate, but selectivities are usually moderate compared with the reactions of ketone silyl enol ethers. Exceptions are a, 8-unsaturated aldehydes, for which diastereo- and enantioselectivity are excellent. The observed erythro selectivity and re-face attack of nucleophiles on the carbonyl carbon of aldehydes are consistent with the aforementioned aldol reactions of ketone enol silyl ethers [47]. 

Schilow recognized that induced reactions fall into two classes. The first class now is called an induced chain reaction, which can be described in terms of an initiation step, a propagation sequence, and a termination step. The other class is the coupled reaction, which can be distinguished from an induced chain reaction by the behavior of the induction factor defined by the ratio equivalents of induced reaction/ equivalents of primary reaction. In an induced chain reaction the induction factor increases without limit as the propagation chain length is increased. In a coupled reaction the induction factor approaches some definite small value such as 1, 2, or 1/2 as the induction reaction is favored. 

The choice of an irreversible color-induction reaction requires more ingenuity and greater care in execution. If the extended molecular unsaturation required to produce the color is too exhaustive, the chiral centers could be systematically eliminated, and must be avoided. Reaction conditions are much more unfavorable. Reagents are generally toxic and corrosive, and reaction conditions are anhydrous, e.g., the measurement of plasma cholesterol using a modified Chugaev reagent. ... 

Although the heading implies that the analyte is achiral, it does not have to be. Greater analytical selectivity can be engendered by specific mutual influences of intrinsic and extrinsic chirality properties. Chirality induction reactions are generally reversible. Many are used extensively in chiral liquid chromatography. ... 

These first cycloadditions are only complete after 72 h at 60°C. When partners are more reactive and the cycloaddition can be catalysed by Lewis acids, it is possible to work at -78°C. Under these conditions, it may be possible to observe high asymmetric induction. Reaction (8.4) of cyclopentadiene with an acrylate derivative of 5-0-trimethylsilyl-a-D-xylofuranose carried out at -78°C in dichloromethane in the presence of TiCl4 gives exclusively the endo adduct ( / , 2 R). This is explained by the formation of an intermediate complex which contains both the dienophile and Lewis acid attached to the chiral sugar inductor (Kunz etal. 1987). 

An advantage of the substrate-based strategy is that the chiral auxiliary is still attached to the molecule after the induction reaction and so the product, 9 in this instance, can be purified as one diastereoisomer before the chiral auxiliary is removed. An example of the asymmetric Strecker reaction in practice is the synthesis of the fat amino acid 16 having an adamantyl group to increase solubility in fats and hence permeability to cell membranes.2 After purification of the amino nitrile 13 hydrolysis gives the amide 14, hydrogenation removes (and sadly destroys) the chiral auxiliary, and a final hydrolysis gives the fat amino acid 16. 

Lewis acid breaks up the closed transition state normally found in thermal reactions. Contrary to the Hiyama-Nozaki reaction the induced stereoselections for allylstannanes-i-Lewis acids are extremely high, due to chelate-Cram controlled mechanisms [reaction (91), Scheme 30] [76]. Reagent controlled diastereoselec-tivity may be exerted in terms of 1,3- [reaction (92)] [77] and 1,5-inductions [reaction (93)] [78]. 

Furuya, M., and Schafer, E., Photoperception and Signalling of Induction Reactions by Different Phytochromes, Trends Plant Sci., 1(9) 301—307, 1996. 

A sample of strontium nitrite has been synthesized and thermally characterized by Tuukkanen and coworkers [63] to investigate its role in the ageing of magnesium-strontium nitrate pyrotechnic compositions in the presence of water vapour. Studies by TG-MS and isothermal microcalorimetry showed that the addition of strontium nitrite to a 50% magnesium-50% strontium nitrate composition eliminated the induction reaction normally observed in closed ampoule studies in air at 50 and relative humidities in the range 65-69%. 

Figure 6 Oxidative stability of oils, (a) Isothermal test experiment, (b) Determination of the activation energy of the induction reaction abbreviations defined in the text)...

Novelization of the alkaloids is easy using the methods known in synthetic production, such as catalytic asymmetric reactions and inductions. Organo-catalytic cascade, asymmetric photocycloaddition, cyclization, and asymmetric decarboxylative allylation are used in total synthesis, as well as catalytic asymmetric induction reactions and condensation of alkaloid molecules (two or more). Novelization of alkaloids by total synthesis is generally used by the pharmacological industry around the globe. 

The spots become visible after a time lag on account of the induction time (i.e., time required for the induction reaction to complete) conditioned by induction properties of the particular compound. The induction time should not be too long because it may cause disappearance of the background owing to iodine sublimation. 

Although there now seems to be good evidence that an hydroxy substituent 3 to the quarternary ammoniiom centre of the chiral catalyst is generally required for significant enantioselectivity to result, it is unfortunate that these structures are also responsible for some of the confusion which exists in the literature, since under basic conditions an optically active epoxide can be formed readily from quarternary derivatives of [I] and [II]. Hence reaction mixtures must be carefully purified before any observed optical rotations can be clearly attributed to an induction reaction. 

In order to produce an asymmetric inductive reaction on the interface of chiral materials, we have conducted the same type of experiments with an optically active surface active agent. Using soybean lecithin ([a] d 7.8°) (XXXVI), styrene was emulsified into the aqueous solution of maleic acid and potassium persulfate was added as radical initiator the copolymerization was carried out at 40°C [22]. 

Because the products of 1,7- and 1,6,7-asymmetric induction reactions have structures frequently found in polyketide compounds and multifunctional groups to be manipulated, these reactions have been applied to synthesize polyketide in short steps. For example, the saii-Helicobacter pylori agent actinopyrone A 313 was synthesized in nine steps from ent -305 (Scheme 8.52). The total synthesis started from the vinylogous Mukaiyama aldol reaction to give the C11-C18 moiety 311 as a single isomer. Protection of the secondary alcohol was followed by DIBAL reduction to give aldehyde 312. As mentioned, the methodology makes it possible to synthesize polyketide compounds in short steps. 

The 1,6,7-asymmetric induction reaction has also been used to obtain anti aldol adducts. In total synthesis of epi-cochlioquinone A 322, an inhibitor of acyl-CoA cholesterol acyltransferase (Scheme 8.53), adduct 315 was submitted to a one-pot protection-ozonolysis procedure to give aldehyde 316. One-pot Henry reaction-dehydration afforded nitroalkene 317, which was converted into... 

Hiroi K, Makino K. Asymmetric induction reactions. III. Palladium-catalyzed asymmetric sulfonylations of allylic sulfinates and acetates with chrial phosphine ligands. Chem. Pharm. Bull. 1988 36 1744-1749. 

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