Sequential Palladium-catalyzed Reactions Research Articles

Competitive pathways in Pd-catalyzed synthesis of arylphenols

Novel developments are described, which have been achieved in the framework of the studies of sequential palladium-catalyzed reactions, involving palladacycle formation with norbornene or norbornadiene via aromatic C–H activation. The use of o-bromophenols as partners of iodobenzenes has led to ring formation after norbornene deinsertion, or to arylphenols, containing a pendant norbornenyl or norbornadienyl group or to vinylarylphenols. The availability of a reductive elimination step drives the reaction course toward a preferential product.

Regioselective functionalization of quinolin-4(1 H)-ones via sequential palladium-catalyzed reactions

A practical and general synthesis of 1,3,6-trisubstituted quinolin-4(1 H)-ones starting from 1-alkyl-6-bromo-3-iodoquinolin-4(1 H)-one is described, based on regioselective sequential palladium-catalyzed cross-coupling reactions, namely Suzuki–Miyaura, Sonogashira and aminocarbonylation reactions, under microwave irradiation. Good substrate generality, ease of execution and practicability make this method exploitable for the generation of libraries of chemically diverse 4-quinolones.

Palladium-catalyzed syntheses of tetrahydrocarbazolones as advanced intermediates to carbazole alkaloids

Two sequential palladium-catalyzed reactions, an intermolecular Stille cross-coupling followed by a recently developed palladium-catalyzed reductive N-heteroannulation, have been employed as the key synthetic steps toward six tetrahydrocarbazolones. The products are advanced intermediates toward a number of naturally occurring carbazole alkaloids.

A highly efficient enantioselective synthesis of 2-methyl chromans via four sequential palladium-catalyzed reactions

An enantioselective synthesis of substituted 2-methyl chromans was accomplished in four steps using four sequential Pd-catalyzed reactions. A study of the key palladium-catalyzed regioselective aryl ether ring formation of two different substrates was also carried out to better understand the factors which affect the selectivity of the reaction.

Palladium-catalyzed synthesis of 1,2-dihydro-4(3 H)-carbazolones. Formal total synthesis of murrayaquinone A

Two sequential palladium-catalyzed reactions are the key steps in a novel synthetic route to 1,2-dihydro-4(3 H)-carbazolones. The steps are an intermolecular Stille cross-coupling followed by a reductive N-heteroannulation. A formal total synthesis of murrayaquinone A, employing this sequence, is reported.

Novel palladium-catalyzed synthesis of 1,2-dihydro-4(3 H)-carbazolones

Two sequential palladium-catalyzed reactions are the key steps in a novel synthetic route to carbazolones, an intermolecular Stille coupling followed by a recently developed palladium-catalyzed reductive N-heteroannulation. A number of functionalized 1,2-dihydro-4(3 H)-carbazolones were prepared using this sequence.

π-Allylpalladium-Mediated Catalytic Synthesis of Functionalized Allenes

Two sequential palladium-catalyzed reactions enable readily available 1,1-dibromo-1-alkenes to be converted into a variety of functionalized allenes (see scheme). The second step proceeds via a π-allylpalladium intermediate, to which a nucleophile attacks highly selectively to give the allene in excellent yield.

A Versatile Enantioselective Strategy Toward L-C-Nucleosides: A Total Synthesis of L-Showdomycin.

Strategies for the synthesis of nucleosides that can provide either L or D isomers become more important as a result of the increasing number of such compounds that are therapeutically useful. The lower toxicity and reduced susceptibility toward metabolism of the L isomers make them particularly interesting. A strategy toward the C-nucleoside analogues has been explored in the context of the synthesis of L-showdomycin. The route involves an asymmetric desymmetrization using palladium catalysis of cis-2,5-diacyloxy-2,5-dihydrofurans available in one step from furan, with carbon nucleophiles. Nucleophilic synthons for a maleimide unit and a methoxycarbonyl unit have been designed. Two sequential palladium-catalyzed reactions introduce both substituents with excellent chemo-, regio-, diastereo-, and enantioselectivity. The presence of a double bond in this doubly alkylated compound at C-3 and C-4 allows easy structural variation. The use of an ester as a hydroxymethyl precursor also introduces a diversity element as well as having importance in its own right. The successful completion of a synthesis of L-showdomycin validates this approach as a viable strategy to C-nucleosides.