Part I. Enantioselective total synthesis of (-)-kendomycin. Part II. Double cyclization via rhodium alkynyl and vinylidene catalysis
The first enantioselective total synthesis of (-)-kendomycin is described. Kendomycin is a biologically active polyketide that possesses a densely functionalized C-aryl glycoside moiety within a fully carbogenic macrocyclic skeleton. A convergent route for the preparation of secomacrocycle 2.107 is outlined in Chapter 2, which allows for quick access to the coupling partners in an efficient and modular fashion. Model studies of the glycosidation reaction provided critical information to identify the appropriate glycosyl acceptors. With the free phenol as a glycosyl acceptor, the key macrocyclization was accomplished by a one pot O-glycosidation-O→ C migration reaction, which represents a novel strategy for the macrocyclic C-aryl glycoside synthesis. The subsequent 2-iodoxybenzoic acid mediated oxidation of monoprotected catechol 2.118 to ortho-quinone 2.119 highlights the unique reactivity and the mild conditions of the hypervalent iodine reagent.
The development of a double cyclization reaction via rhodium alkynyl and dialkyl vinylidene catalysis is described in the final chapter. On the basis of the stoichiometric metal alkynylide alkylation precedents and the discoveries from our laboratory, substrates with general skeleton of 3.48 were designed to establish the catalytic conditions. In the presence of triethylamine and a complex derived from [Rh(COD)Cl]2 and P(4-F-C 6H4)3, 3-haloalkyl-1,6-enynes were converted to various 5,6-fused carbo-, oxa-, and aza-bicyclic dienes under mild conditions. By replacing the alkene moiety with other reactive components, this alkylative approach was extended to construct other ring structures, thus demonstrating the potential and the generality of the current methodology.