Sulfuryl chloride, regioselectivity

Further studies of electrophilic substitution using the 2,3-dihydrothiazolo analogue (320) show that regioselective bromination can be effected in the 7-position (347) at low temperature. Chlorination with sulfuryl chloride, however, occurs exclusively in the 5-position. The 5-chloro derivative (348) can be further nitrated in the 7-position. By analogy, bromination of quinoline analogues (349) occurs in the azine ring, in the 5-position. The [3,2-a]pyrimidine analogue (350 R=H) similarly yields the 7-bromide. The activation by... 

Phenols are monochlorinated regioselectively nsing sulfuryl chloride and amines (snch as di-iec-bntylamine) as the catalysts in nonpolar solvents (eqnation 82). In a typical experiment an ortho/para ratio of 22 was obtained with yields of abont 90% . 

In the absence of the amines, the yields of the chlorinated prodncts are very low. Thus the addition of 8 mol% of the primary or secondary amines increased the conversion of phenol from 7.2 to 97.5% and the reaction was complete in less than one hour. The reaction is highly regioselective, giving almost exclusively the ortito-chlorinated products. The highest o/p ratio of 65.9 was observed when di-isobutylamine was used as the catalyst. The reaction is completely nonregioselective in the absence of the amine catalysts. The use of two equivalents of sulfuryl chloride resulted in the formation of 2,6-dichlorophenol as the predominant product (equation 83). Tertiary amines such as triethylamine, on the other hand, gave low o/p ratios, typically ranging from 0.5 to 1.3. 

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