Substituents table

The procedure has been found to be compatible with a variety of carbocyclic substituents. Table 5.1 provides some examples of the reaction. 

One of the virtues of the Fischer indole synthesis is that it can frequently be used to prepare indoles having functionalized substituents. This versatility extends beyond the range of very stable substituents such as alkoxy and halogens and includes esters, amides and hydroxy substituents. Table 7.3 gives some examples. These include cases of introduction of 3-acetic acid, 3-acetamide, 3-(2-aminoethyl)- and 3-(2-hydroxyethyl)- side-chains, all of which are of special importance in the preparation of biologically active indole derivatives. Entry 11 is an efficient synthesis of the non-steroidal anti-inflammatory drug indomethacin. A noteworthy feature of the reaction is the... 

Other functional groups that are easily differentiated are cyanide (5c =110-120) from isocyanide (5c = 135- 150), thiocyanate (5c =110-120) from isothiocyanate (5c = 125 - 140), cyanate (5c = 105- 120) from isocyanate (5c = 120- 135) and aliphatic C atoms which are bonded to different heteroatoms or substituents (Table 2.2). Thus ether-methoxy generally appears between 5c = 55 and 62, ester-methoxy at 5c = 52 N-methyl generally lies between 5c = 30 and 45 and. S-methyl at about 5c = 25. However, methyl signals at 5c = 20 may also arise from methyl groups attached to C=X or C=C double bonds, e.g. as in acetyl, C//j-CO-. 

Bodi MO theory and experimental measurements provide a basis for evaluation of the energetic effects of conjugation between a double bond and adjacent substituents. Table 1.16 gives some representative values. The theoretical values AE are for the isodesmic reaction... 

Limited data suggest that the cntropic term may be as important as the enthalpic term in determining polymerizability. The value of AA(, is lowered >20 J moh1 K."1 by the presence of an a-melhyl substituent (Table 4.10, compare entries for AN and MAN, S and AMS). This is likely to be a eonscqucncc of the polymers from a-methyl vinyl monomers having a more rigid, more ordered structure than those from the corresponding vinyl monomers. 

Reactions with anhydrides afford interesting compounds having a carboxylic acid function (Table 26, entries 5 and 7 and Figure 40). It is notable that in the case of succinic anhydride, if the reaction is carried out at 25 °C, only one substitution occurs on the nitrogen atom, if the temperature is increased to 180 °C, there is a second substitution giving rise to a heterocyclic substituent (Table 26, entries 5-8). 

The general trend is that boron enolates parallel lithium enolates in their stereoselectivity but show enhanced stereoselectivity. There also are some advantages in terms of access to both stereoisomeric enol derivatives. Another important characteristic of boron enolates is that they are not subject to internal chelation. The tetracoordinate dialkylboron in the cyclic TS is not able to accept additional ligands, so there is no tendency to form a chelated TS when the aldehyde or enolate carries a donor substituent. Table 2.2 gives some typical data for boron enolates and shows the strong correspondence between enolate configuration and product stereochemistry. 

Dimethylcyclohexene is an example of an alkene for which the stereochemistry of hydrogen chloride addition is dependent on the solvent and temperature. At —78° C in dichloromethane, 88% of the product is the result of syn addition, whereas at 0° C in ether, 95% of the product results from anti addition.8 Syn addition is particularly common with alkenes having an aryl substituent. Table 4.1 lists several alkenes for which the stereochemistry of addition of hydrogen chloride or hydrogen bromide has been studied. 

We have examined succinoglycans from a number of bacteria. The polymers from different organisms have different proportions of acid substituents (Table 1). They also have slightly different physical properties, particularly viscosity (Figure 2). In some cases it may be useful to select a polymer with particular characteristics. 

The diastereomeric pentacoordinated bromostannanes 49 and 50 were found to equilibrate at — 13°C in toluene to a mixture of diastereomers27. The composition of the equilibrium mixture is dependent upon the R substituent (Table 4). As the size of this group is increased, the equilibrium is shifted in favor of the sterically less congested diastereomer 49. 

Incidentally, oxidation data of the pyrrole monomers show an interesting increase in oxidation potentials when containing heavier substituents (Table 25). However, the ionization potential of N -methylpyrrole (7.95 V) is smaller than that of pyrrole (8.21 V). The accepted linear relationship between ionization potential and oxidation potential210 would have it the other way round. Considering, however, that trimethylsilyl and trimethylgermyl groups are weak electron donors211, it is plausible that a nonelectronic effect is responsible for the observed trend and the potential shifts are associated with steric effects. 

Allenyltrimethylsilanes add to ethyl glyoxalate in the presence of a chiral pybox scandium triflate catalyst to afford highly enantioenriched homopropargylic alcohols or dihydrofurans, depending on the nature of the silyl substituent (Tables 9.39 and 9.40) [62]. The trimethylsilyl-substituted silanes give rise to the alcohol products whereas the bulkier t-butyldiphenylsilyl (DPS)-substituted silanes yield only the [3 + 2] cycloadducts. A bidentate complex of the glyoxalate with the scandium metal center in which the aldehyde carbonyl adopts an axial orientation accounts for the observed facial preference ofboth additions. 

Not surprisingly, these additions favor the anti products in ratios that reflect the steric requirement of the aldehyde substituent (Table 9.54). Additions to chiral a-methyl-/ -oxygenated propanals show remarkable reagent control (Eq. 9.145). The anti adducts are formed to the exclusion of the syn diastereomers when enantiomeric mesylates are employed with the (R)-aldehyde. 

In situ transmetallation of allenylpalladium intermediates with Sml2 provides a route to allenylsamarium reagents [123]. These undergo protonolysis with alcohols to afford mainly allenes (Table 9.59). Additions to ketones yield either allenylcarbi-nols (A) or homopropargylic alcohols (B) depending on the allene substituents (Table 9.60). 

The kinetic behavior of 1,3-dienes has also been investigated in as much detail as that of alkenes52. Some data are collected in Table 4. The effect of a vinyl group on the reactivity of carbon-carbon double bonds toward p-methoxydiphenylcarbenium ion has been compared with that of methyl and phenyl substituents (Table 5). Whereas butadiene reacted 21 times faster than propene, the reactivity of isoprene was significantly lower... 

Severd exceptions of this type have been found. Lactones 38 bearing nitrophenyl or nitrobenzyl substituents (Table 9) have been shown to depart from the two-point lactone model (Sect. IV-B) (75). 

For characterization of the steric and electronic contributions of the substituents, the constant c was introduced and defined as the intercept difference for the basic tetrahydrooxazine system 389 and the compound in question. A positive c value indicates stabilization a negative c value means a destabilizing effect of the substituents (Table VIII). 

The electronegative influence of the thiadiazole system greatly increases the acidity of substituents (Table 2). The effect is further enhanced in the 1-monoxide and 1,1 -dioxide analogues. The ionization constants of 4- and 5-hydroxy-2,l,3-benzothiadiazoles were determined in water <70AC(R)80l>. 

Dihydroartemisinin 29a and anhydrides or acyl chlorides in the presence of DMAP, pyridine, or triethylamine gave the a-esters 139 the base thus has no effects on the stereochemistry of the acyl substituent (Table 10) <2002EJ0113>. 

What is the origin for this anomalous effects of para substituents The inspection of ZFS parameters clearly indicates that there are no significant changes in /D values as the para substituents are varied (Table 9.14). These observations indicate that the para substituents do not have much effect on the geometries of brominated DPCs. The reactivities of brominated DPCs toward typical triplet quenchers, that is, oxygen and 1,4-cyclohexadiene, are also not significantly affected by the para substituents (Table 9.14). 

A very large acceleration in kisc is observed with p-methoxy and dimethylamino substituents (Table 11.2). This observation is consistent with the solution-phase photochemistry of p-methoxy and p-dimethylaminophenyl azides.The Me, CF3, acetyl, fluoro, and chloro substituents are not sufficiently strong n donors or acceptors to significantly influence the size of feisc (Table 11.2), but the strong n... 

Very large acceleration in /cisc is observed with para-methoxy and dimethylamino substituents (Table 2). This is consistent with the solution-phase photochemistry of para-methoxy and para-dimethylaminophenyl azides. ... 

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