Condensed heteroaromatic ring systems. Part 24. Synthesis of rigidin, a pyrrolo[2,3-d]pyrimidine marine alkaloid
The marine alkaloid rigidin has been synthesized from 2,4-dimethoxy-7-phenylsulfonylpyrrolo[2,3-d]pyrimidine. Lithiation of the pyrrolo[2,3-d]pyrimidine followed by electrophilic substitution with N, 4-dimethoxy-N-methylbenzamide afforded a 6-(4-methoxy)benzoyl derivative which by alkaline hydrolysis and subsequent iodination was converted into 2,4-dimethoxy-5-iodopyrrolo [2,3-d] pyrimidin-6-yl 4-methoxyphenyl ketone. The palladium-catalysed arylation of this with 2-(4-methoxyphenyl)-1,3,2-dioxaborinane followed by demethylation with boron tribromide gave rigidin.