Selective side-chain oxidation of peralkylated pyrrometheneBF2 complexes

Treatment with 2,3‐dichloro‐5,6‐dicyano‐1,4‐benzoquinone (DDQ) oxidized 2,6‐diethyl‐1,3,5,7,8‐pentamethylpyrromethene–BF2 complex 1, 13,14‐trimethyl‐2, 3, 4, 5,9,10,11,12‐octahydroindomethene–BF2 complex 5, and 1,3,5,7,8‐pentamethyl‐1,2,3,5,6,7‐hexahydropyromethene–BF2 complex 8 to the weakly fluorescent 3‐formyl, 5‐oxo, and 8‐formyl derivatives 4, 6, and 9, respectively. The dye 1 was oxidized by lead tetraacetate to 1,7,8‐trimethyl‐2,6‐diethyl‐3,5‐diacetoxymethylpyrromethene–BF2 complex 12 [λf (ethanol) 538 nm, Φ 0.62, λlas (ethanol) 555–570 nm]. Catalytic reduction (Pd/C) converted the aldehyde 4 to 2,6‐diethyl‐3‐hydroxymethyl‐1,5,7,8‐tetramethylpyrromethene–BF2 complex 10 [λf (ethanol) 537 nm, Φ 0.70, λlas (ethanol) 547–575 nm].