Reaction of 1-benzoselenopyrylium salts with grignard reagents: Formation of 2,4-disubstituted selenochromenes and their conversion into the corresponding 1-benzoselenopyrylium salts^†

Treatment of 2-tert-butyl-1-benzoselenopyrylium salts 1A and 2-phenyl-1-benzoselenopyrylium salts 1B with an alkyl(phenyl)magnesium halide resulted in nucleophilic addition at the C-4 position to give the corresponding 2,4-disubstituted 4H-selenochromenes 2A and 2B in good yields, respectively. The obtained selenochromenes 2 were then easily converted into the 4-substituted 2-tert-butyl-1-benzoselenopyrylium salts 6A by treatment with triphenylcarbenium tetrafluoroborate in high yields. The 4-substituted 2-phenyl derivatives 6B were also obtained in a similar manner. The reaction of the unsubstituted 1-benzoselenopy-rylium salt 1C with an alkylmagnesium halide is also described.