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Cyclizations, involving chlorosulfonic

Several other heterocyclic compounds can be prepared by cyclizations involving the use of chlorosulfonic acid. For instance, benzylaminoacetals 14, on treatment with the reagent, cyclize to the corresponding isoquinolines 15 (Equation 5). ... [Pg.260]

Z)-y Azido a,j3-ethylenenitriles cyclized with chlorosulfonic acid in chloroform under mild conditions to give the corresponding pyrrolotetrazoles. The cyclization involves a double ring closure and was stereospecific only the Z-azidonitriles reacted (see Chapter 4, p 120). [Pg.262]

Poliak et al. claimed that the reaction of biphenyl 32 with excess chlorosulfonic acid (six equivalents) at 18 °C affords dibenzothiophene-5,5-dioxide-3,7-disulfonyl chloride 34, but more recent attempts to reproduce this result were unsuccessful and only the 4,4 -disulfonyl chloride 33 (80%) was isolated. However, the cyclized product 34 was obtained in good yield (72%) when biphenyl 32 was heated with a large excess of chlorosulfonic acid (20 equivalents) at 150 °C (4 hours) (Equation 11). The reaction presumably involves the formation of the intermediate biphenyl-2,4,4 -trisulfonyl chloride, 35 which subsequently cyclizes with loss of hydrogen chloride to give the dibenzothiophene dioxide 34. Further study of the action of chlorosulfonic acid on biphenyl 32 showed that the optimum yield of the 4-sulfonyl chloride (43%) was derived from treatment of 32 with the reagent (1.5 equivalents) in thionyl chloride as solvent at 0 °C (1 week). The best yield (89%) of the 4,4 -disulfonyl chloride 33 was also achieved by treatment of the hydrocarbon 32 with chlorosulfonic acid (three equivalents) in thionyl chloride at room temperature (1 week). [Pg.42]

An improved procedure for the chlorosulfonation of substituted diaryl sulfones involves heating the appropriate 4,4 -dialkyl or dihalodiaryl sulfone with chlorosulfonic acid (2-4 equivalents) at 140-150 °C and subsequent treatment with thionyl chloride (6-10 equivalents). The action of chlorosulfonic acid on propiophenone (ethyl phenyl ketone 226) results in a novel cyclization reaction yielding 3-chloro-2-methylbenzothiophene-1,1-dioxide 227 (Scheme 2). The reagent similarly caused smooth cyclization of Mannich bases 228, the reaction again proceeding via the enolic sulfonic acid to yield the cyclic sulfone 229 (Equation 72). ... [Pg.79]

Benzil 258 undergoes a novel cyclization reaction on treatinent with chlorosulfonic acid (six equivalents) at 40 °C (2 hours) to 5ueld 3-chloro-2-phenylbenzofuran-6,4 -disulfonyl chloride (259, 60%). The mechanism originally proposed for the reaction involved cyclization to the benzofuran ring system prior to sulfonation. However, this mechanism is probably incorrect and has been modified so that sulfonation occurs before cyclization as shown in Scheme 4,... [Pg.86]

In contrast, when the reaction was carried out at 150 °C, the enaminoketone 265 cyclized to form the benzoxathianesulfonyl chloride 267 (Equation 84). Benzoylacetone (268) reacts with excess chlorosulfonic acid (10 equivalents) at room temperature (three hours), followed by treatment with dimethylamine to give the bisdimethylamide (269, 33%) (Scheme 5). In this sequence, direct sulfonation occurs on the methylene carbon atom of the enolic form and subsequent reaction is via the chlorohydrin intermediate and involves expulsion of ketene as has previously been observed in the chlorosulfonation of benzylide-neacetone (see p 82). In the reaction, sulfonation of the phenyl ring occurs in the position meta to the electron-withdrawing carbonyl moiety as would be anticipated. [Pg.88]

Benzilic acid 294 was claimed to react with chlorosulfonic acid (12 equivalents) in boiling chloroform to give 4,4 -dichlorosulfonylbenzophenone 292, however repetition of the reaction afforded 9-chlorofluorene-2,7-disulfonyl chloride 295 (38%). The proposed mechanism for this conversion is shown in Scheme 8 and involves protonation of the alcoholic hydroxyl group followed by loss of water. The carbocation 296 is formed before cyclization to fluorene-9-carboxylic acid, so that subsequent sulfonation should occur in the 2,7-positions. ... [Pg.94]


See other pages where Cyclizations, involving chlorosulfonic is mentioned: [Pg.281]    [Pg.991]    [Pg.92]    [Pg.991]    [Pg.20]   


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