Substitution in the Ring

Substitution o- to the thiol group occurs and can be used for heterocycle formatbn as in the synthesis of the tetrahydropyridothbchromone shown. A mixture of ethyl 4-oxopiperidine-3-carboxylate hydrochloride was added slowly to stirred polyphosphoric acid at 100X, and after 4 hours reaction at 

A cyclic thiocoumarin derivative was prepared from 4-methoxybenzylidene thiosalicylaldehyde in a novel use of the three C unit of carbon suboxide. 2-[(4-methoxphenylimino)methyl]thiophenol suspended in ether was treated at -10X with ethereal carbon suboxide during 30 mins, and after stirring at 0 C for 2 nours and completion of reaction over 3-4 days the product, thtocoumarin-3-(N-4-methoxyphenyl)amide, was obtained in 51% yield (ref. 125) by way of a postulated lactam. 

An ether of an of a oxime of a formylamino derivative apparently difficult to prepare in the usual way was obtained indirectly by way of an iminoether, ethyl N-(3,5-dichIoro-4-mercaptophenyl)-N-ethoxyformamidine in high yield (ref.126). 

The preferential dealkylation of a combined thio and 0-alkyl ether was selectively chemically achieved either at the O or the S atom by appropriate choice of reagent. Sodium iso-propylthiolate at 120°C added to 3-(methylthio)anisole in hexamethylphosphorictriamide in a nitrogen atmosphere followed after 2.5 hours by acidification gave 3-(methylthio)phenol in 88% yield, while sodium alone in hexamethylphosphorictriamide resulted in selective 

Unlike the synthesis of phenols from non-aromatic sources that of thiophenol by similar methodology is virtually unknown. The synthesis shown of the diacetate of a tricyclic compound containing an o-substituted thiophenol system would appear to be applicable to the simpler central portion and to bicydic analogues. Ethyl 4-(1-benzyl-2-thioxo-pyrrolidin-3-yl)-5-(diazoacetyl)-pyrrole -2-carboxylate in dichloromethane was treated with boron trifluoride etherate in the same solvent and after 15 mins, the intermediate shown resulted which in a sealed tube (under vacuum) with acetic acid/acetic anhydride (3 1) at 132°C during 90mins. produced by a Pummerer rearrangement, ethyl 

---

We have studied the dependence of the oxidation peak potentials on the substitution in the rings A and B for 16 structurally different 2-hydroxychal-cones [61]. The increase in the number of electron donating groups in ring B resulted in the decrease of the peak potentials while the peak potentials remain virtually the same when the munber of electron-donating groups in ring A was... 

Trivial names of substituted benzenes retained for present use include toluene, styrene and stilbene, but only for derivatives when substituting in the ring (see Section 4.5.6.2 and Table 4.13). 

The spiroindolinonaphthoxazine derivatives became commercially important compounds once detailed research work led to products which overcame many of their initial weaknesses, such as relatively poor fatigue resistance and a poor colour range (550-620 nm). The important positions for substitution in the ring of (1.11) are the 5-position which has a large effect on the colour, the 6 -position, which has a major effect on both the colour and properties such as optical density (OD) and molar absorption coefficient and the alkyl group on position 1, which has a kinetic effect on the rate of loss of colour back to the colourless state. ... 

Although some electrophilic reagents cause substitution in the ring at C-3 and C-5, very reactive compounds, such as trimethyloxonium tetra-fluoroborate Meerwein s reagent)and nitronlum tetraHuo-... 

This does not occur in the case of catalyst and reactants here described. With Bronsted-type catalysis, the reaction between the benzoyl cation, Ph-C" =0, and the hydroxy group in phenol is quicker than the electrophilic substitution in the ring. This hypothesis has been also confirmed by running the reaction between anisole and benzoic acid in this case the prevailing products were (4-methoxy)phenylmethanone (the product of para-C-benzoylation) and methylbenzoate (obtained by esterification between anisole and benzoic acid, with the co-production of phenol), with minor amounts of phenylbenzoate, phenol, 2-methylphenol and 4-methylphenol. Therefore, when the 0 atom is not available for the esterification due to the presence of the substituent, the direct C-acylation becomes the more favored reaction. 

The 13C NMR parameters of 169 azoles with no other substitution in the ring show the effect of N-substituents (88MRC134). 

The explanation of this result and of the peculiar points in the bromlnation of trlmethylene is as follows a small amount of hyurobroaic acid is always at first formed (by the action of moisture or by a little bromine substituting in the ring),this hydrobromic acid adds to the ring to give a normal bromide of the formula Br-CMa-CH, in the one caee and [Pg.965]

The kind of halogen atom affects the substitution in the ring with the nitro group. Table 100 shows the results of investigations by Sandin and J. R. W. Williams [3]. J. D. Roberts and co-woikeis [3a] obtained similar results by using isotope dilution analysis. 

Table 5 demonstrates that substitution in the ring decreases monomer polymerizability because the intramolecular interactions between substituents are always higher in the polymer than in the cyclic monomer. Thus,... 

Nature and Degree of Substitution in the Ring. Little is known about the effect of introducing hetero atoms into the ring and the ease of ring closure. Ring closure with w-bromoalkylamines Br(CH2) NH2 is extremely slow for = 9 or 11. 

This preference for one site of cyelization over another, however, is not fixed, but depends on the substitution in the ring, the structure of the reacting centers, and the presence [Pg.532]

Addition of acyl anion equivalents (propenal d reagents) to ketones provides general access to a -hy-droxy enones. In an application of this method to pentaimulation, the trimethylsilyl- or ethoxyethyl-pro-tected cyanohydrins of a, -enals were used." The derived tertiary acetates undergo elimination (p-TsOH/benzene) to the divinyl ketones which cyclize in the acidic reaction medium (equation 25)." In some cases the a -hydroxy or a -silyloxy enones underwent cyclization but in much lower yields. Substitution in the ring and on the double bonds is compatible. 

Ease of Substitutipn.— The substitution products of toluene are much more readily formed than similar ones in the case of benzene. The presence of a methyl group substituted in the benzene ring seems to make the compound more easily susceptible to further substitution in the ring itself. 

It is best to speak at this time of hydrocarbons derived from benzene by the substitution in the ring of unsaiurated open chain radicals. Just as the homologues of benzene are prepared by substitution of a saturated paraffin radical, methyl, ethyl, propyl, etc., in the benzene ring, so other series of hydrocarbons have been obtained by substituting radicals of the unsaturated open chain hydrocarbons of the ethylene and acetylene series. These new compounds will be poorer in hydrogen than the benzene series by two and four atoms respectively. 

We referred to the fact that substitution in the benzene ring takes place more easily with toluene than with benzene itself, i.e., the presence of a substituted methyl group increases the ease of further substitution in the ring. Also oxidation takes place more easily when substitution has already occurred and still more easily if the side chain is likewise substituted. 

The sulphonic acids, it will be recalled, are strong acids, their acid character being due to the remaining acid hydroxyl left in the compound. Sulphuric acid is di-basic and only one of the two hydroxyls is eliminated by the substitution in the ring. Nitric acid, however, is mono-basic and possesses only one acid hydroxyl. 

---