Syntehsis of Substituted Tetrahydrofuran by Electrophile-Induced Cyclization of 4-Pentene-1,2,3-triols- An Example of 5-exo versus 5-endo Cyclization Governed by the Electrophile

摘要

Differently protected 4-pentene-1,2,3-triols 5-8 were obtained from glyceraldehyde and submitted to iodine-based electrophile-induced cyclization to give tetrahydrofuran derivatives 10 and 18, with high chemo-, regio-, and stereoselectivity, through a 5-exo cyclizaton process. However, when an electrophiilic selenium reagent was treated with similar alkene triols 5, 7, and 8, the product depended on the protecting group at the primary hydroxy moiety. Thus, while compounds 5a and 5b, unportected at the primary hydroxy group, give compounds 26 and 27, and 32 and 33, respectively, through a 5-exo cyclization process, compounds 7 and 8, protected at the primary hydroxy group, give the 5-endo cyclization products 22-25 and 28-31 in good yields. The electrophile-induced cyclization of 4-pentene-1,2,3-triols to give tetrahydrofuran derivatives can be directed towards a 5-exo process by the use of iodine or, when the primary hydroxy group is unprotected, selenium. When the primary hydroxy group is protected, use of selenium results in 5-endo cyclization.