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.