Synthesis of aromatic bisabolene natural products via palladium-catalyzed cross-couplings of organozinc reagents

Aromatic bisabolene derivatives were prepared by two methods involving cross-coupling of organozine reagents. The first synthesis of (+/-)-glandulone A (10), as well as syntheses of (+/-)-curcuhydroquinone (8) and (+/-)-curcuquinone (9), were accomplished via coupling of a secondary alkyl zinc reagent (1,5-dimethyl-4-hexenylzinc halide, 18) to protected bromohydroquinones using Pd(dppf)Cl-2 as catalyst. Coupling of arylzinc halides with alkenyl triflate 16 using Pd(PPh3)(4) catalyst provided a number of bisabolene derivatives and led to syntheses of dehydro-alpha-curcumene (2), (+/-)- curcuphenol (3), and (+/-)-elvirol (13). A high-yield synthesis of the (+/-)-heliannuol D precursor 29 is also reported using this method.