The convergent syntheses of the C (1–32) and C (33–46) domains of phorboxazole B are described. An iterative cyclocondensation strategy exploited the Jacobsen hetero-Diels– Alder (HDA) reaction as a platform for the synthesis of both the C (5–9) and C (11–15) tetrahydropyran rings. The use of 2-silyloxydiene coupling partners bearing an increasing resemblance to the phorboxazole skeleton was found to lead to a reduction in ...