Lodolactonization lactone synthesis

Bromolactonization. A key step in a synthesis of ramulosin (4) requires halolac-tonization of the yi.b-unsaturated acid 1, which can result in a "y- or a 8-lactone. Bromolactonization results mainly in the desired 8-lactone (2), which is converted in two steps into 4. lodolactonization of 1 results mainly in the undesired y-lactone and a mixture of isomeric 8-lactones. 

A synthesis of j8-lactones, performed originally on a conformationally rigid molecule, has been found to be of general applicability. Treatment of an open-chain iSy-unsaturated carboxylic acid salt (37) with bromine gives the bromolactone (38) as kinetic product (Scheme 13) this reaction is successful even with but-3-enoic acid. lodolactonization may also be kinetically controlled, the difference in product ring size being due to the different electro-philicities of the two halogens. 

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