An Efficient Methodology for the Synthesis of the 3-Styryl Coumarin

Coumarins (or benzopyranones), whether naturally occurring or synthetic, have attracted the interest of the scientific community due to their broad pharmacological activities,1,2 such as antiprotozoal,3 anticancer,4 antibacterial,5 among others. Depending on the nature and substitution pattern, coumarins show exceptional optical properties,6 as they constitute the largest class of fluorescent dyes,7 widely used as emission layers in organic light-emitting diodes (OLED),8 optical brighteners,9 nonlinear optical chromophores,10 fluorescent whiteners,11 fluorescent labels and probes for physiological measurement12 and more recently, in labelling13 and caging.14 Developments from the last decade show that the introduction of appropriated substituents into the coumarin ring contribute to structures with improved photophysical and spectroscopic proprieties.15 Many articles dealing with their synthesis, reactivity and spectral profile have been published. In particular, it seems that the presence of an aryl or heteroaryl moiety on the 3-position of the coumarinic system induces specific activities.16 The objective of this work is the synthesis of 3-styrylcoumarin using the regioselective and highly efficient Heck coupling reaction17. To carry out the synthesis of 3-styrylcoumarin, the synthesis of 3-bromocoumarin was essential which was accomplished with oxone18 and HBr on reaction with coumarin. Subsequent Suzuki cross-coupling reaction19 of 3-bromocoumarin with potassium vinyltrifluoroborate20 allowed 3-vinylcoumarin, the scaffold used to obtained 3-styrylcoumarin. The increase in conjugation reflects on the absorbance of the synthesized compound revealing pronounced bathochromic shift and hyperchromic effect