Efficient syntheses of 6-prenylcoumarins and linear pyranocoumarins:: Total synthesis of suberosin, toddaculin, O-methylapigravin (O-methylbrosiperin), O-methylbalsamiferone, dihydroxanthyletin, xanthyletin and luvangetin

Synthesis of naturally occurring 6-prenylcoumarins (1a, 2c and 3a) and their derivatives 1c, 1d, 1e, 2d and 3b-d starting from 2-prenyloxybenzaldehydes (8, 12 and 14) using tandem Claisen rearrangement and Wittig reaction is described. The coumarins 1a, 1e and 2c are converted to dihydropyranocoumarins (5a-e). The conversion of dihydroxanthyletin 5a and dihydroluvangetin 5d to the naturally occurring linear pyranocoumarins xanthyletin 6a and luvangetin 6b is also described.