aldehyde 30 containing already the carbamate function. A HWE reaction produced the substrate for an intramolecular Heckcoupling. In contrast to the Stille cyclization, the Heck cyclization produced only the desired 14E,16E-diene. Elaboration of the C-19 side chain led to the key lactone 38. asymmetric synthesis - dihydroxylations - Heckreaction - macrocycles - natural products