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 '-neolignanand its enantiomer with higher enantiomeric excess were synthesizedfrom all cis-tetra-substituted tetrahydrofuran withan iodomethyl group by a hydride or H-2 ring-expansion reaction.The normal hydride reductions of C-I bonds of tetra-substitutedtetrahydrofurans bearing iodomethyl groups were observed in other2,3-cis-stereoisomers of tetra-substituted tetrahydrofuransto give tetra-substituted tetrahydrofurans bearing 7,8-cis and 8,7 '-neolignan structures. The phytotoxicities of theirsynthesized compounds were compared with previously synthesized 7,8-trans-8,7 '-neolignans bearing tetra-substituted tetrahydrofuransto find out the highest phytotoxic tri-substituted tetrahydropyrantype 8,7 '-neolignan.