Synthesis of Novel Cavitand Host Molecules via Palladium-Catalyzed Aryloxy- and Azidocarbonylation

Novel, elongated, resorcine[4]arene-based cavitands were synthesized via various consecutive reaction steps, including homogeneous catalytic aryloxy- and azidocarbonylation processes. The effects of carbon monoxide pressure and temperature on the conversion were examined in aryloxycarbonylation. It was revealed that a reaction temperature of 100 °C is required to achieve complete conversion both with monodentate (PPh₃) and bidentate (Xantphos) phosphines at different carbon monoxide pressures (1-40 bar). Using ten different phenols as O-nucleophiles, partial hydrolysis of the esters to the corresponding carboxylic acids took place-i.e., 58-90% chemoselectivities toward esters were obtained. Moreover, the influences of temperature, reaction time and the catalyst ratio on the selectivity and conversion were described in the case of azidocarbonylation reaction. The formation of the acyl azide with high chemoselevtivity can be achieved at room temperature only. The higher reaction temperatures (50 °C) and higher catalyst loadings favor the formation of the primary amide. The characterization of the target compounds (esters and acyl azides) was carried out by IR and ¹H and ¹3C NMR. The discussion of the influences of various parameters is based on in situ NMR investigations.

Turn-on and Turn-off Fluorescent Probes for Carbon Monoxide Detection and Blood Carboxyhemoglobin Determination

Water-soluble, carbazole-based two-photon excitable fluorescent probes MPVC-I ("turn-on") and MPVC-II ("turn-off") are rationally designed and synthesized for the selective monitoring of carbon monoxide (CO). Both probes can effectively measure carboxyhemoglobin (HbCO) in the blood of the animals exposed to a CO dose as low as 100 ppm for 10 min. The palladium catalyzed azidocarbonylation reaction was optimized to improve the sensing efficiency.