Total Synthesis of Malyngamides K, L, and 5-epi-C and Absolute Configuration of Malyngamide L

An accelerated, enantioselective, and general synthetic route to a class of malyngamides, K (1), L (3), and 5 ''-epi-C (4), bearing a cyclohexenone ring or a heavily oxygenated six-membered ring and a vinyl chloride structural motif was developed. The key step was the Suzuki cross-coupling reaction of boronic acids 6-8 with unsaturated carboxylic amides 5a,b possessing the chlorovinyl iodide functionality for the construction of the skeletons of 1-4. The key intermediates 10a,b were prepared using Ogilvie's method for the construction of the chlorovinyl iodide functionality. The NMR data of the synthetic compound 2 were in full agreement with those of the reported product, and the discrepancy in the specific rotation data suggested that the correct structure of malyngamide L should be 3, in which the absolute configuration of the amine part was enantiomeric to that in compound 2. Then the absolute configuration of the stereogenic center at C(3 '') and C(4 '') in malyngamide L was confirmed by synthesis of compound 3.