“…Several types of catalysts were introduced previously for this reaction, such as piperidine, 17 tetrabutylammonium bromide, 18 I 2 , 19 sodium dodecyl sulfate, 20 1buthyl-3-methylimidazolium tetrafluoroborate, 21 1-ethyl-3-(3-sulfopropyl)-benzimidazolium trifluoromethanesulfonate, 22 para-dodecylbenzenesulfonic acid/piperidine, 23 3-methyl-1-(4-sulfonic acid)butylimidazolium hydrogen sulfate, 24 B(HSO 4 ) 3 , 25 polyvinylpyrrolidone-supported nickel nanoparticles, 26 poly(4-vinylpyridine)-supported ionic liquids, 27,28 and cellulose sulfonic acid. 29 Also, biscoumarin derivatives have been prepared by the condensation of 1,2-diols and 4-hydroxycoumarin using Pb(OAc) 4 . 30 However, many of these methods have some drawbacks, such as a requirement for either a long reaction time or harsh reaction conditions, provide low yields, include laborious work-up procedures, inefficiency of method when aliphatic aldehydes are used in the reaction, and the use of unrecyclable, hazardous or difficult to handle catalysts.…”