Reaction yield procedure

The conversion of a carbonyl compound by ammonium polysulphide solution into an amide with the same number of carbon atoms is known as the Willgerodt reaction. The procedure has been improved by the addition of about 40 per cent, of dioxan or of pyridine to increase the mutual solubility of the ketone and aqueous ammonium polysulphide the requisite temperature is lowered to about and the yield is generally better. 

The applicability of the two-parameter equation and the constants devised by Brown to electrophilic aromatic substitutions was tested by plotting values of the partial rate factors for a reaction against the appropriate substituent constants. It was maintained that such comparisons yielded satisfactory linear correlations for the results of many electrophilic substitutions, the slopes of the correlations giving the values of the reaction constants. If the existence of linear free energy relationships in electrophilic aromatic substitutions were not in dispute, the above procedure would suffice, and the precision of the correlation would measure the usefulness of the p+cr+ equation. However, a point at issue was whether the effect of a substituent could be represented by a constant, or whether its nature depended on the specific reaction. To investigate the effect of a particular substituent in different reactions, the values for the various reactions of the logarithms of the partial rate factors for the substituent were plotted against the p+ values of the reactions. This procedure should show more readily whether the effect of a substituent depends on the reaction, in which case deviations from a hnear relationship would occur. It was concluded that any variation in substituent effects was random, and not a function of electron demand by the electrophile. ... 

More functionalized 5,6-dihydro-2H-pyran-derivatives 71 and 72 have been prepared [26] by cycloaddition of 1 -methoxy-3-trialkylsilyloxy-1,3-butadienes 69 with t-butylglyoxylate (70) (Scheme 5.6). Whereas thermal reactions did not occur in good yields because of the decomposition of the cycloadducts, application of pressure (10 kbar) allowed milder conditions to be used, which markedly improved the reaction yields. The use of high pressure also gives preferentially en Jo-adduct allowing a stereocontrolled synthesis of a variety of substituted 5,6-dihydro-2H-pyran-derivatives, which are difficult to prepare by other procedures. 

The advantage of these polymeric reagents is surprisingly simple reaction course, especially in the isolation step. In the majority of cases all extraction procedures are unnecessary. The reaction yields are high and comparable with (good optimized) yields of NBS and PHT processes. 

A simple, high-yield procedure for the conversion of ArTlXj into ArjTlX compounds has recently been described 90). This symmetrization reaction, the mechanism of which is not known, can be effected by treatment of the ArTlX2 compound either with triethyl phosphite or with hot aqueous acetone. As a wide variety of ArTlXj compounds can now be easily prepared by electrophilic thallation of aromatic substrates with thallium(III) trifluoroacetate (q. v.), symmetrization represents the method of choice for the preparation of the majority of ArjTlX compounds. Only about twenty mixed compounds, RR TIX, have been prepared so far, and the only general synthetic procedure available consists of a disproportionation reaction between an RTIX2 species and another organometallic reagent [e.g., Eqs. (5)-(7)]. 

There are several methods available for the detection or measurement of amine groups in proteins and other molecules. Accurate determination of target amine groups in molecules before or after modification may be important for assessing reaction yield or suitability for subsequent crosslinking procedures. The following methods use commercially available reagents and are easily employed to detect primary amines with simple spectrophotometric measurement. 

For the decabromodiphenyl oxide (DBDPO) pyrolysis reactions, two different procedures were used to synthesize the series of brominated diphenyl oxides and dibenozofurans employed as the relative retention time standards AlBr3/Br2 in ethylene dibromide and Fe° (metal)/Br2 in tetrachloroethylene. The rate of the initial bromination steps in the former reaction was so rapid that only the higher degree of bromination adducts could be isolated. The rate of the Fe°/Br2 reaction was found to be much slower, especially during the initial stages, and these reactions yielded a broader range of relative retention time reference peaks. 

Table 1 Suzuki/Stille coupling reaction yield (direct coupling vs. two-step procedure)...

S)-(-)-CITRONELLOL from geraniol. An asymmetrically catalyzed Diels-Alder reaction is used to prepare (1 R)-1,3,4-TRIMETHYL-3-C YCLOHEXENE-1 -CARBOXALDEHYDE with an (acyloxy)borane complex derived from L-(+)-tartaric acid as the catalyst. A high-yield procedure for the rearrangement of epoxides to carbonyl compounds catalyzed by METHYLALUMINUM BIS(4-BROMO-2,6-DI-tert-BUTYLPHENOXIDE) is demonstrated with a preparation of DIPHENYL-ACETALDEHYDE from stilbene oxide. A palladium/copper catalyst system is used to prepare (Z)-2-BROMO-5-(TRIMETHYLSILYL)-2-PENTEN-4-YNOIC ACID ETHYL ESTER. The coupling of vinyl and aryl halides with acetylenes is a powerful carbon-carbon bond-forming reaction, particularly valuable for the construction of such enyne systems. 

The postmodification strategy, in which apoly(glycydyl methacrylate-co-ethylene dimethacrylate) monolith was activated with hydrogen sulfide to a thiol-modified monolith and subsequently derivatized with an 0-9-(tert-butylcarbamoyl)quinine selector by radical addition reaction, yielded slightly less efficient capillary columns. However, this procedure has the advantage that only minute amount of chiral selector are needed to end-up with a useful enantioselective capillary column [84]. 

In some cases special synthetic methodologies were applied to increase reactions yields or to satisfy green chemistry requirements. For example, Yao and co-authors [41] successfully carried out solvent-free three-component reaction of 5-ammotetrazole, aromatic aldehydes, and acetoacetic acid in the presence of inexpensive and commercially available sulfamic acid as catalyst. The yields of the MCRs were rather low but the whole procedure was facile, economic, and eco-friendly. 

Brassilexin 48 and sinalexin 49 are among the most potent phytoalexins produced by economically important cruciferous plants. The most efficient preparation of brassilexin 48, sinalexin 49, and analogues 52 reported uses a Vilsmeier formylation-amination of readily available indoline-2-thiones 50 followed by an aqueous ammonia work-up procedure with subsequent oxidation of the 3-(amino)methyleneindoline-2-thione intermediates 51 using iodine in pyridine (Scheme 10) <20010L1213, 2005JOC1828>. The reaction yields are dictated by the efficiency of the... 

Oxime reduction is a very efficient procedure for obtaining racemic A7-hydroxy ami no acids in good yields. 19 31-361 TV-Hydroxylamine and O-protected A-hydroxylamines react smoothly and rapidly with a-oxo acid derivatives 23 to give the corresponding oximes 24. Acids 24 (R2= OH) can be reduced with NaBH3CN or LiBH3CN (Scheme 7) to give TV-hydroxyamino acids 25 (R2= OH)/31 but reaction yields are unsatisfactory for esters 24 (e.g., R2= OEt) or... 

The synthesis of ethyl 3,3-diethoxypropanoate, 5, described here implies acylation of an enol ether followed by a haloform reaction. The procedure is superior to other methods, which afford mixtures of acetals and acrylates,4 give only moderate yields,5 6 7 require the troublesome use of ketene8 or expensive ethyl propiolate,9 10 11 need palladium(ll) catalysis,12 or equipment for electrochemical reactions.13... 

While different enzyme reactions yield different results in different solvents, thus rendering comparison difficult, a procedure akin to a standard protocol for conducting enzyme reactions in organic solvents has been developed. It calls for... 

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