Total Synthesis of Diocollettines A via an Acid-Promoted Oxa-Michael-Aldol-Acetalization Cascade.

A diastereo- and enantioselective total synthesis of diocollettines A with an unusual oxygen-containing tricyclic ring system has been achieved in 63% overall yield from commercially available 3-phenylpropanal via four steps. The key feature of the present synthesis is an exclusively diastereoselective cascade sequence composed of a trans-selective oxa-Michael addition of 1,3-dihydroxyacetone to a 2,3-dihydropyrylium ion intermediate, intramolecular aldol-type reaction, and intramolecular acetalization.