The reaction of dodec-11-ene-1,6-diynes or their heteroatom congeners with a hydrosilane catalyzed by Rh(acac)(CO)2 at ambient temperature and pressure of CO gives the corresponding fused 5-7-5 tricyclic products, 5-oxo-1,3a,4,5,7,9-hexahydro-3H-cyclopenta[e]azulenes or their heteroatom congeners, in excellent yields through a unique silicon-initiated cascade carbonylative carbotricyclization (CO-SiCaT) process. It has also been found that the 5-7-5 fused tricyclic products can be obtained from the same type of enediynes and CO through a novel intramolecular [2+2+2+1] cycloaddition process. The characteristics of these two tricyclization processes and the fundamental differences in their reaction mechanisms are discussed. This novel higher-order cycloaddition reaction has also been successfully applied to the tricyclization of undeca-5,10-diyn-1-als, affording the corresponding 5-7-5 fused-ring products bearing a seven-membered lactone moiety. Related [2+2+2] tricyclizations of enediyne and diynal substrates are also discussed. These newly discovered reactions can construct multiple bonds all at once, converting linear starting materials to polycyclic compounds in a single step. Thus, these new processes provide innovative routes to functionalized polycyclic compounds that are useful for the syntheses of natural and unnatural products.

[reaction: see text] The first Rh-catalyzed intramolecular [2 + 2 + 2 + 1] cycloaddition reaction of enediynes and CO is reported. This novel higher order cycloaddition process gives the corresponding 5-7-5 ring systems in high yield and selectivity. This process is another significant addition to the arsenal of cycloaddition-based synthetic methods, which provide powerful tools for rapid and efficient construction of complex polycyclic systems.

Myers's methodology for enantioselective amino acid synthesis was employed to prepare the N-Boc didehydroleucine amide derivative 15 and to effect its conversion into the acylfuran intermediate 17. Coupling of 19 (R = H) with N-(isooctanoyl)serine provided the furan-based analogue 4 of eponemycin (de = 96 %), a peptide epoxide with potent cyto-