Regio‐ and stereoselective formation of tri‐ and tetrasubstituted tetrahydrofuranylidenes from hydroxy ketosulfones

Four tri‐ and tetrasubstituted E ‐1‐(benzenesulfonyl)‐1‐tetrahydrofuranylidenes 7‐10 were synthesized from their corresponding α′‐benzenesulfonyl‐γ‐hydroxyketones 1 in good yields. The examination of the regio‐and steroselectivity of these thermally induced reactions shows preference for both, the exocyclic nature of the double bond and the E ‐geometry in all tetrahydrofuranylidenes described. Structural assignments are based on infrared, 1 H nmr, 13 C nmr, 2D 1 H‐ 1 H and 13 C‐ 1 H correlation spectra. In contrast to tetrahydrofuranylidenes 7‐10 , hemiketal 6 shows no tendency towards dehydration under the thermal reaction conditions used. This paper discusses the extent and limitations of this method as a tool of synthetic utility for the regio‐and stereoselective preparation of the target compounds.