5-endo-dig cyclisations of 3-alkyne-1,2-diols using iodine as the electrophile proceed smoothly to deliver excellent yields of the corresponding β-iodofurans. The necessary precursors are available from a number of different approaches, notably regioselective bis-hydroxylation of conjugated enynes and the addition of acetylides to α-hydroxy carbonyl groups. The initial iodofurans can be homologated using a number of strategies, ranging from various transition metal-catalysed couplings to halogen–metal exchange and subsequent coupling with an electrophile. Hence, this method overall represents a flexible, relatively brief and very efficient approach to a variety of highly substituted furans. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

5-endo-trig cyclisation of the (Z)-hydroxyalkenoate 17 using iodine as the electrophile gave a good yield of the β-hydroxytetrahydrofuran 18, probably via the corresponding iodohydrin. A variety of one-carbon degradation methods were then used to generate precursors to (−)-muscarine (25d). An alternative strategy featured control of a 5-endo-trig iodocyclisation by an allylic hydroxyl group, which can be used for the highly stereocontrolled synthesis of hydroxy-iodotetrahydrofurans 28. Application of this strategy to the (Z)-alkenediol derivative 38 led to an excellent yield of the tetrahydrofuran 39 when iodine monobromide was used as the electrophile. Two simple and efficient transformations then gave the (+)-muscarine precursor 40b. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004)