Synthesis of the C22-C26 tetrahydropyran segment of phorboxazole by a stereoselective prins cyclization

[formula: see text] Tetrahydropyran rings are found in many complex natural products, and the segment-coupling Prins cyclization is an effective strategy for their synthesis. We report a four-step, stereoselective synthesis of the C20-C27 tetrahydropyran segment of phorboxazole. The key step is a Prins cyclization induced by catalytic BF3.OEt2.