1 - tetrahydrofuran 5-alkoxy-1 -alkene

An intermolecular iron-catalyzed ring expansion reaction involving epoxides and alkenes provided tetrahydrofurans via radical processes <07CEJ4312>. Cp2TiCl is able to promote cyclization of 2,3-epoxy alcohols containing a p-(alkoxy)acrylate moiety to form tetrahydrofurans <07TL6389>. As shown in the following example, an intramolecular addition of carbon radicals to aldehydes was reported to afford tetrahydrofuran-3-ols... 

The halocyclization of 1 -benzyloxy-3-hydroxy-4-alkenes or l-benzyloxy-3-alkoxy-4-alkenes, carried out with iodine in tetrahydrofuran, in the presence of sodium hydrogen carbonate, or with bromine in dichloromethane, gives tetrahydrofurans in good yield. 1,2-Asymmetric induction is very effective and m-2.3-disubstituted tetrahydrofurans are the major products, in analogy with the cyclization of the corresponding diols, unless the double bond has Z configuration16,25. 

Finally, it is worth mentioning that cycloetherification of alkoxy-3-alkenes, performed with phenylselenyl chloride in dichloromethane in the presence of potassium carbonate, is effective for the preparation of 2,5-cw-disubstituted tetrahydrofurans in good yield and with very high stereoselection129 136. 

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