Bromo chalcones

If the alkyne in the second step is a 1-aryl propargyl alcohol the product is a bischalcone as a consequence of a CIR-CIR sequence. Furthermore, it is also possible to perform CIR-Heck and CIR-Suzuki sequences if alkenes or boronates and potassium carbonate are added after completion of the initial CIR step. Here again, the gradual differences in reactivity in the oxidative addition between an electron-deficient and an electro-neutral carbon-bromine bond can be readily exploited for selective cross-coupling, first to furnish an aryl propargyl alcohol that is slowly isomerized upon base catalysis to give the bromo chalcone for further cross-coupling. 

With a catalytic amount of diisobutyi telluride method B. Chalcone (0.5 mmol), cesium carbonate (1.0 mmol), ( )-3-bromo-l-trimethylsilylprop-l-ene (0.75 mmol), diisobutyi telluride (0.1 mmol), THF (5 cm ) and water (5 mm ) were mixed in a reaction tube and stirred at 50°C for a specific period of time. After 28 h, additional trimethylsilylallyl bromide (0.25 mmol) was added and stirring continued for 20 h. When the reaction was complete (monitored by TLC), work-up as for method A and flash chromatography of the residue on silica gel afforded the product, of purity >98% (GC). 

The A-bromosuccinimidc-hydrogen fluoride/pyridine system was employed to add bromine monofluoride to chalcones in dimethylformamide with the formation of. mt-2-bromo-3-fluoro-... 

Another option for Sonogashira coupling as an initiator of sequential catalysis is the coupling isomerization reaction (CIR) of electron-deficient halide and 1-aryl propargyl alcohols giving rise to the formation of chalcones [115, 116]. Based upon the CIR of electron-deficient halides 163 and l-(p-bromo phenyl) propyn-l-ol (164) Muller and Braun [117] presented a consecutive... 

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