Syntheses of Tetrahydropyran Type 8,7'-Neolignans Using a Ring-Expansion Reaction and Tetrahydrofuran Type 8,7'-Neolignans to Discover a Novel Phytotoxic Neolignan.

One novel tri-substituted tetrahydropyran type 8,7'-neolignan and its enantiomer with higher enantiomeric excess were synthesized from all cis -tetra-substituted tetrahydrofuran with an iodomethyl group by a hydride or H 2 ring-expansion reaction. The normal hydride reductions of C-I bonds of tetra-substituted tetrahydrofurans bearing iodomethyl groups were observed in other 2,3- ci s-stereoisomers of tetra-substituted tetrahydrofurans to give tetra-substituted tetrahydrofurans bearing 7,8- cis and 8,7'-neolignan structures. The phytotoxicities of their synthesized compounds were compared with previously synthesized 7,8- trans -8,7'-neolignans bearing tetra-substituted tetrahydrofurans to find out the highest phytotoxic tri-substituted tetrahydropyran type 8,7'-neolignan.