Lithiation of dibenzothiophene

Lithiation of dibenzothiophene (THF, 0°C, BunLi/ether) gives the 4-lithio derivative (314) <74AHC(16)181>. 

Competitive metallation experiments with IV-methylpyrrole and thiophene and with IV-methylindole and benzo[6]thiophene indicate that the sulfur-containing heterocycles react more rapidly with H-butyllithium in ether. The comparative reactivity of thiophene and furan with butyllithium depends on the metallation conditions. In hexane, furan reacts more rapidly than thiophene but in ether, in the presence of tetramethylethylenediamine (TMEDA), the order of reactivity is reversed (77JCS(P1)887). Competitive metallation experiments have established that dibenzofuran is more easily lithiated than dibenzothiophene, which in turn is more easily lithiated than A-ethylcarbazole. These compounds lose the proton bound to carbon 4 in dibenzofuran and dibenzothiophene and the equivalent proton (bound to carbon 1) in the carbazole (64JOM(2)304). 

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>. 

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