C-3 substitution

Formed commercially by the polymerization of S, NajCOj and PhX in a sealed container at 275--370 C, substituted derivatives are known but not fully evaluated. Used as high-temperature adhesives, for laminates and in coatings. 

The sodio derivative, which is prepared by mixing alcoholic solutions of the ester and of sodium ethoxide, condenses with alkyl halides to yield mono-alkyl C-substituted products, for example ... 

The mono-alkyl C-substituted derivatives of ethyl acetoacetate upon treatment with sodium ethoxide and another molecule of alkyl halide afford the di-alkyl C-substituted products... 

The sodiocompound may be written [CHtCOOCjHjij] Na, and it must always be home in mind that the anion is mesomeric. The system reacts smoothly with an alkyl halide to give a C-substituted malonic ester, evidently through the carbanion (I) ... 

Alkylation of the sodio derivative affords the C-substituted cyanoacetic ester, which when heated with dilute acid gives the mono-substitut acetic acid. 

Anomalous Fischer cyclizations are observed with certain c-substituted aryl-hydrazones, especially 2-alkoxy derivatives[l]. The products which are formed can generally be accounted for by an intermediate which w ould be formed by (ip50-substitution during the sigmatropic rearrangement step. Nucleophiles from the reaction medium, e.g. Cl or the solvent, are introduced at the 5-and/or 6-position of the indole ring. Even carbon nucleophiles, e.g. ethyl acetoacelate, can be incorporated if added to the reaction solution[2]. The use of 2-tosyloxy or 2-trifluoromethanesulfonyloxy derivatives has been found to avoid this complication and has proved useful in the preparation of 7-oxygen-ated indoles[3]. 

The stronger directing effects present in the indoline ring can sometimes be used to advantage to prepare C-substituted indoles. The aniline type of nitrogen present in indoline favours 5,7-substitution. After the substituent is introduced the indoline ring can be aromatized by dehydrogenation (see Section 15.2 for further discussion). A procedure for 7-acylation of indoline... 

At temperatures >300° C, substituted pyrroHdines can be obtained by reaction of substituted a2iridines (R = CH, C2H ) and conjugated olefins X = CN, CO2CH2, CH=CH2) with C—C cleavage in the three-membered ring (214—216). 

Metallacarboranes in Catalysis. Perhaps the most intensely studied of all metaHacarborane complexes is the exopolyhedral metaHacaiborane [61250-52-0] shown in Figure 23a, and its cage C-substituted derivatives. The three available... 

The H NMR spectrum of pyridazine shows two symmetrical quartets of an A2X2 or A2B2 type dependent on the solvent and concentration. The satellites have been used to obtain all coupling constants. Spectra of C-substituted pyridazines, methylthio- and methylsulfonyl-pyridazines, both as neutral molecules and as cations, N-1 and N-2 quater-nized species, pyridazinones, hydroxypyridazinones, A-oxides and 1,2-dioxides have been reviewed (b-73NMR88> and are summarized in Tables 6, 7 and 8. 

The thermal reactions of pyrroles include the rearrangement of A-substituted pyrroles to C-substituted derivatives (Scheme 1). The rearrangement of A-acylpyrroles has also been reported to occur in the vapour phase on irradiation. 

Substituted pyrazoles are formylated (Vilsmeier-Haack reaetion) and aeetylated (Friedel-Crafts reaction) at C-4 (B-76MI40402). Both hydroxy and amino substituents in positions 3 and 5 facilitate the reaetion (80ACH(105)127,80CHE1), but the heteroatoms eompete with the C-substitution. For instanee, when the amino derivative (91 R = = Ph, R = H)... 

Dihydroxy- 4-methoxybenzophenone OH 0 OH CH.O-( )-C -( Substituted dihydroxybenzophenone Stronger than the monohydroxy compound but some absorption in the visible range. 

C + A B. The minimal cutsets of E2 are thus C and E3 is already in 1 uced form having minimal cutsets B and C. Substituting El = A+B+C, hence. has three minimal cutsets A, B, and C. Finally, substituting the expressions for, and E2 into the equation for T, expanding and applying the absorption law gives ... 

Annular prototropie tautomerism of 1,2,3-triazole (v-triazole) and its C-substituted derivatives involves the equilibrium of three possible isomers 24a-24c. In the ease of the parent eompound (R = H), 24a and 24c are degenerate isomers (Seheme 11). 

Aromatic compound Halogen Temp. ( C) Substitution products Ref. 

Mainly C-substituted pyrroles have been synthesized by application of the Knorr pyrrole synthesis however N-substituted pyrroles can also be prepared, when starting with secondary aminoketones, e.g. bearing an N-methyl or N-phenyl substituent. 

A wider range of C-substituted imidazoles is commercially available, and the combination of these with the reaction shown in Scheme 2.1-2 permits the formation of many different possible starting materials. In some cases, however, it may still be necessary to carry out synthesis of the heterocycle from first principles. For reasons of space, this topic is not covered here. 

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