Double iodocyclization with

Treatment of compound 22 with an excess of iodine in THF at 0 °C resulted in the formation of compound 23, the free hydroxyl group being favored in the nucleophilic attack to the iodonium ion. It is worth of note that, despite the presence of two double bonds, at 0 °C the reaction is regioselective. Increasing the temperature to 20 °C, the second iodocyclization with debenzylation occurs, affording compound 24 in 60% overall yield. 

Cyclizations of chloral hemiacetal derivatives of cyclic allyl alcohols were regio- and stereo-selective (Table 6, entry 1), but a mixture of regioisomers was obtained from analogous derivatives of acyclic allyl alcohols with a nonterminal double bond.93 Hemiacetal derivatives of allyl alcohols with a terminal vinyl group have been cyclized with mercury(II) acetate to give acetal derivatives of threo 1,2-diols with moderate selectivities (equation 54 and Table 15, entries 1 and 2).147 Moderate to excellent stereoselectivity has been observed in the iodocyclizations of carbonate derivatives of allyl alcohols (entries 3-5).94a The currently available results do not provide a rationale for the variation in observed stereoselectivity. 

In contrast, cyclizations of /V-alkoxy derivatives with iodine are much less selective (Table 30, entry 3), and similar results are observed with systems containing internal double bonds of either ( )- or (Z)-configuration.238 The stereoselectivity of the aminomercuration reaction of /V-methyl derivatives has been reported to be controlled by the choice of mercury(II) salt and solvent (entries 6 and 7).244 Cyclization with platinum salts showed little selectivity (entry 8).239 An iodocyclization of a complex N-alkyl system has been used in a recent synthesis of (+)-croomine.238... 

Iodocyclization of trichloroacetimidates forms trans-1,3-oxazolines with moderate to good stereoselectivity (equation 118).234 Cyclizations of systems with internal double bonds (equation 119) generate 5-exo products only if the double bond has a (Z)-configuration (entries 2 and 3) or an oxygen substituent is attached to the allylic carbon (entries 3 and 4). Wc-153 ,i57b,254c... 

The intramolecular iodocyclization of 3-penten-l-ols performed with iodine/sodium hydrogen carbonate in dry acetonitrile allows tetrahydrofurans to be obtained via a 5-endo-trig process. This method can result in obtaining 2,5-tram- or 2,5-m-tetrahydrofurans. depending on the geometry of the double bond127 - no. 

Disubstituted A-alkoxypyrrolidines were obtained by iodocyclization of 1-substituted 4-alkenyl-jV-alkoxyamines by the addition of iodine in acetonitrile in the presence of sodium hydrogen carbonate. Moderate 1,3-asymmetric induction was observed with little dependence on the bulk of the R1 substituent. The 2,5-/rc n.v-pyrrolidine trans-3 was the predominant product, unless the disubstituted double bond had E configuration77. The iodides were transformed to alcohols with net retention of configuration. 

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