Synthesis of (±) lupinifoun, di-o-methyl xanthohumol and isoxanthohumol and related compounds

Abstract

Nuclear prenylation of naringenin ( 7) with 2-methylbut-3-en-2-ol in the presence of boron trifluoride etherate gives a mixture of 6-C-prenyl-( 11), 8-C-prenyl-( 15) and 6,8-di-C-prenyl-( 8) derivatives. On formic acid cyclisation, 11 yielded two monodihydropyrans ( 12 and 13), but 15 afforded only one viz 16; similarly 8 formed the bisdihydropyran 10. Methylation of 8-C-prenyl naringenin ( 15) with Me 2SO 4 resulted in the formation of di-O-methyl derivatives of xanthohumol ( 22) and isoxanthohumol ( 23). Cyclodehydrogenation of 6,8-di-C-prenyl-naringenin ( 8) with DDQ gave a mono-C-prenyl-2,2-dimethylpyran ( 1) corresponding to (±) lupinifolin. The angular isomer ( 2) was also formed. The structure of natural flemichin-B therefore needs further consideration. Similarly, cyclodehydrogenation of 6-C-( 11)- and 8-C-prenyl-( 15) naringenins afforded the corresponding linear ( 24) and angular ( 25) derivatives which have been characterized by conversion into known chalcones 26 and 27 by O-methylation.