Dibenzothiophenes acylation

Friedel-Crafts acylation of dibenzothiophene with succinic anhydride is known to occur in the 2-position, yielding y-oxo-2-dibenzothiophene-but3Tic acid (135a). Subsequent Wolff-Kishner reduction and internal cyclization yields 7-keto-7,8,9,10-tetrahydrobenzo[6]naphtho[2,3-d]thio-phene (136a). - This reaction has been extended to 4-methyldibenzo-... 

Dibenzothiophene carbamate 396 was converted to the corresponding l,3-oxazin-2-one derivatives 397 in a two-step, one-pot procedure. Lithiation of 396 gave a bis-anion intermediate, treatment of which with ketones led to cyclization to tetracyclic l,3-oxazin-2-ones 397 (Equation 43). In the similar reaction of the analogous dibenzofuran carbamate, a hydroxymethyl-substituted acylic compound was formed <1998J(P1)457>. 

Dibenzothiophene derivatives are available from benzo[Z> jthiophenes by this procedure. In this case the major product of Friedel-Crafts acylation is the 3-substituted derivative cf. Chapter 3.14) and reaction of succinic anhydride gives as the major product the keto acid (319), which is then reduced and cyclized via the acid chloride to 4-keto-l,2,3,4-tetrahydrodibenzothiophene (320). Better yields were obtained when 3-methoxycar-bonylpropionyl chloride was substituted for succinic anhydride in the first step (69JHC771). 

The reductive cleavage of dibenzothiophene and carboxylation and acid-catalysed cyclization of the resulting biphenyl derivative affords dibcnzo[/(//]thiopyran-6-onc <1957JOC851>. The same product can be obtained by the intramolecular acylation of 2 -(benzylsulfanyl)biphenyl-2-carboxylic acid via the acid chloride (Scheme 196) < 1996H(43 )2567>. 

The reaction of isatin 7 with acylated dibenzothiophene [81, 109, 116], dibenzofuran [116], and dibenzopyran [72] with the general formula 124 and also the reaction of the isatins 59 with acetylphenothiazine [72] and acetylthianthrene [117] with the general formula 125 gave the corresponding quinolinecarboxylic acids 126 and 127, having a tricyclic condensed system with a heterocycle as substituent at position 2. 

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