Reaction of 5-methylene-1,3-dioxepanes derived from oxaphospholanes and paraformaldehyde with trimethylsilyl trifluoromethanesulfonate in the presence of a base yielded novel, exo formyl tetrahydropyran derivatives in good yields.
The reaction of 6-methylene-l,3-dioxepanes derived from 3-hydroxyalkyltriphenylphosphonium salts and paraformaldehyde with trimethylsilyl trifluoromethanesulfonate in the presence of N,N-diisopropylethylamine yielded novel 4-formyltetrahydropyrans. 3-Methylenetetrahydropyrans were synthesized by the reaction of 4-hydroxyalkyltriphenyl-phosphonium iodides with DBU and paraformaldehyde. 2,3-Dihydro-