Iodolactonization epoxide synthesis

The heading substitution reactions has been used to describe the conversion of a stereogenic center to another. Of course, this means that the substrate stereogenic center has had to be obtained by one of the reaction types outlined earlier, from the chiral pool, or by resolution. Reactions that fall into this category include epoxide and cyclic sulfate openings and iodolactonizations (Chapter 22). Perhaps the most important reaction of this type for asymmetric synthesis is allylic substitution in the presence of a transition metal catalyst. 

Demole and Enggist (1968) synthesized ( )-dihydroactinidiolide from p-cyclohomogeranic acid (2,6,6-trimethyl-1-cyclohexene-1-acetic acid) with two variants. Cyclization of the epoxide gave a hydro-xylactone which was dehydrated, or the acid was transformed into the iodolactone which was dehydro-halogenated. A similar synthesis with bromine was carried out by Sakan et al. (1967). 

The use of iodolactonization in the synthesis of 5-lactones is demonstrated in routes to a prostaglandin endoperoxide analogue, and to the antibiotic malyngolide. The latter compound (164) has also been prepared as a mixture of C-2 epimers by lactonization of the epoxide (163). Stereoselective sul-phenyl-lactonization plays an important role in a synthesis of octahy-droleukotrienes, and cyclization of the cyclopropyl acid (165) leads to the lactone (166). A spirocyclic dilactone has been prepared and undergoes... 

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