Phorocantholide

A simpler version of this annelation has been used to obtain phorocantholide (5) via a hemiketal (4). 

The general attractiveness and flexibility were illustrated by acquisition of 2,3-disubstituted quinolines (27) and also phorocantholide (28), a natural 10-membered ring lactone constituent of an insect secretion. The use of a. -unsaturated ketones as initial receptors lends extra scope to the overall sequence, and permits preparation of substituted 9-, 10- and 11-membered unsaturated macrolides (29) bearing double bonds of fixed geometry at specific positions in lactone rings (Scheme 24). As illustrated in Scheme 24, intramolecular cyclizations of the vie groups may also lead to regiospecifically substituted... 

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