i) C6H5 -Cl on reaction with Mg in presence of dry ether which product is obtained ?
Answers
Explanation:
ABRAMOVITCH ET AL.: AROMATIC SUBSTITUTION 1753
the 2,3-isomer should be forined predominantly in these cases. The choice of such a sub-
stituent was made difficult by the fact that most of the common electron-attracting groups
(e.g. NO,, C02R) themselves react with the organolithium reagent. It was decided to
examine the reactions when R = SO3CHB and Br, and also to try and determine whether
coordination of the organolithiuln reagent at the pyridine nitrogen atom was important
in determining the preferential orientation of the entering nucleophile, as had been sug-
gested (5). The latter seemed unlilrely since it has been reported that the reaction of
benzyllnagnesium chloride with 3,4-lutidine rnethiodide (where further coordination at
nitrogen is not possible) gives the 1,2-dihydro-2-benzyl derivative (6). Other examples of
such reactions are known (7). To this end it was decided to study the reaction of phenyl-
lithium with N-benzylpyridinium chloride and with 3-methyl-N-benzylpyridinium chlor-
ide. Finally, it was suggested by Brown and Harcourt (8) that a "strong" nucleophilic
reagent would attack the quinoline ring preferentially at C(2), whereas a "weak" one
would attack it at the position of lowest nucleophilic atom localization energy, namely
C(4). Phenyllithium is considered to be a strong nucleophile and it was, consequently, of
interest to determine the orientation of the entering phenyl group with greater certainty
than had been done before. Ziegler and Zeiser (9) carried out this reaction and obtained
2-phenylquinoline together with a small amount of a lower-melting compound which,
they suggested but did not prove, was 4-phenylquinoline. Gilman and Gainer (10) re-
peated the reaction and obtained 2-phenylquinoline and 2,2-diphenyl-1,2-dihydroquino-
line, but no 4-phenylquinoline. It was decided to re-examine this reaction and to attempt
to detect by gas chromatographic analysis any 4-phenylquinoline formed.
Methyl 3-pyridinesulphonate (IV) could not be prepared by any of the standard re-
actions. Pyridine-3-sulphonic acid was recovered unchanged on treatment with diazo-
methane. When the acid chloride (V) was treated with methanolic sodium inethoxide the
betaine (VI) was obtained, identical with that prepared from potassium pyridine-3-
sulphonate and methyl iodide in the presence of aqueous sodium hydroxide (11). It is
conceivable that the required ester may have been formed in this reaction but that it
underwent self-alkylation in the working-up process. Pyridine-3-N,N-diethylsulphona-
mide (VII) was used instead of the ester in the reaction with phenyllithium. When VII
I
CHa
VI VII
in excess was treated with phenj~llithium and the product worked up by colun~n chroma-
tography only one product other than starting material was isolated, in low yield (20%
based on phenyllithium). On the basis of its analysis and infrared spectrum (bands at
1578, 778, and 730 cm-l (12, 13)) this is thought to be 2-phenylp~ridine-3-N,-V-diethyl-
sulphonamide (11; R = S02NEt2). No 2,5-isomer could be detected among the reaction
products. The orientation observed is thus in accord with that expected on the basis of
the electron-attracting character of the substituent.
The reaction of phenyllithium with 3-bromopyridine gave a mixture of neutral and basic
products. Each of these fractions was analyzed by gas-phase chromatography. The neutral
fraction was found to contain bromobenzene (43.47, of neutral components) together