Sulfones Friedel-Crafts cyclization

The Friedel-Crafts cyclization of biphenyl-2-sulfonyl chloride to give dibenzothiophene sulfone has been described (55%) ° however, thermal cyclization in octachloronaphthalene at 250°, under nitrogen, is reported to yield dibenzothiophene itself rather than the sulfone (47%). Reaction of biphenyl compounds with oleum (H2SO4 + SO3) to yield derivatives of dibenzothiophene 5,5-dioxide is widely used for the preparation of dyestuff intermediates (Section VI, E, 2). A typical example is shown in Eq. (3), starting from o-tolidine. ... 

Benzo[6]thiophenes ran also be prepared indirectly by Friedel-Crafts cyclization of styrylsulfonyl chlorides (59JA2000) or 2-phenylethanesulfonyl chlorides (53JA3359). Since these cyclizations produce either benzothiophene sulfones or dihydrobenzothiophene sul-fones, further oxidative and/or reductive steps are required to obtain benzo[ Jthiophenes. 

The synthesis of rofecoxib can be achieved by several different routes (Drugs Fut., 1998). A highly efficient synthesis for rofecoxib was recently described (Therien et al., 2001). As illustrated in Scheme 79, acetophenon (i) is prepared according to the literature, by Friedel-Crafts acylation with thioanisole. Oxidation with MMPP (magnesium monoperoxyphthalate hexahydrate) affords the sulfone (ii), which is reacted with bromine in chloroform in the presence of a trace amount of AICI3, to give (iii). Bromoketone (iii) is than coupled and cyclized in a second step, one-pot procedure with phenylacetic acid. Firstly, the mixture of bromoacetophenone (iii) and phenylacetic acid in acetonitrile is treated with... 

Cyclization of allylic sulfones In the presence of aluminum chloride, allylic sul-fones can undergo intramolecular cyclization of the Friedel-Crafts type with displacement of the sulfone group. Examples are the cyclization of 1 and 4 to 2 and 5. respectively. 

Sulfones can also be used in Friedel-Crafts-type cyclizations. One example is shown in Scheme 85, where the cyclization in the presence of aluminum chloride of the allylic sulfone occurred in high yield, showing that sulfones can also become electrophiles. Since a tertiary carbanion has about the same stability as a simple allylic cation, tertiary sulfones can also be cyclized (Scheme 85). These last examples illustrated the umpolung provided by the sulfone since carbanion chemistry was used to introduce the 2-methyl groups. 

AUylic and tertiary alkyl sulfones can also participate in electrophilic cyclizations in the presence of aluminum chloride (Friedel-Crafts reaction eq 16). ... 

Functionalized alkenes containing a phenyl or carboxylic acid group at appropriate distance from the double bond undergo intramolecular cyclization during the sulfonation. On reaction of ( -4-hexenoIc add with SO3 a sulfo 5 lactone is formed (eq 8), and a Friedel-Crafts type cyclization is observed on sulfonation of ( )-5 phenyl-2-pentene (eq 9) both cyclizations proceed quantitatively and stereospedfically. 

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