Pd-Catalyzed Umpolung Chemistry of Glycal Acetates and Their [2,3]-Dehydrosugar Isomers.

Glycals and their [2,3]-dehydrosugar derivatives have commonly been used in synthetic chemistry as electrophiles. Here we report a Pd-catalyzed polar inversion (umpolung) of this reaction, where the glycals and isomers can be used as nucleophiles. The reaction showed high regio- and stereoselectivity in the presence of numerous aromatic and aliphatic aldehydes.

Palladium-Catalyzed Asymmetric Decarboxylative Addition of β-Keto Acids to Heteroatom-Substituted Allenes.

The Pd-catalyzed asymmetric addition reaction of β-keto acids to heteroatom-substituted allene is reported. This reaction generates β-substituted ketones in an asymmetric manner through a branch-selective decarboxylative allylation pathway. The reaction accommodates various alkoxyallenes as well as amidoallenes.

Bifunctional Urea/Hg(OAc)-Mediated Synthesis of 4-Aryl-6-oxycarbonyl-2-pyrones and 2-Pyridones from Dithiomalonate and β,γ-Unsaturated α-Keto Esters.

Disubstituted 2-pyrones and 2-pyridones were obtained by bifunctional urea-catalyzed Michael addition/lactonization or lactamization followed by a Hg(OAc)- or Hg(OAc)/DBU-mediated hydrolysis/decarboxylation/dehydrogenation process. This one-pot two-stage protocol enabled the rapid synthesis of 4,6-disubstituted 2-pyrones and 2-pyridones from dithiomalonate and β,γ-unsaturated α-keto esters in practical yields under mild reaction conditions. Additionally, the obtained 2-pyridones were facilely transformed to 2,4,6-trisubstituted pyridines in excellent yields.

Flexible Total Synthesis of 11-Deoxylandomycins and Their Non-Natural Analogues by Way of Asymmetric Metal Catalysis.

A de novo first collective total synthesis of 11-deoxylandomycins is reported. A signature step is featured by the Pd-catalyzed asymmetric addition of alcohol to ene-alkoxyallenes that assembles oligomeric 2,3,6-trideoxyoligosaccharides. The unique feature of the protocol is illustrated by a flexible access to various natural 11-deoxylandomycins as well as non-natural analogues.

A Convergent Synthetic Strategy towards Oligosaccharides containing 2,3,6-Trideoxypyranoglycosides.

A de novo synthetic strategy for the production of oligosaccharides containing 2,3,6-trideoxypyranoglycoside is reported. The key event is the Pd-catalyzed asymmetric diastereoselective hydroalkoxylation of ene-alkoxyallene-linked glycosidic fragments. The utility of this approach was demonstrated by the activation-free, stereodivergent, and convergent synthesis of various 2-deoxyoligosaccharides, as well as their aglycon conjugates.

Bioinspired Synthesis of Chiral 3,4-Dihydropyranones via S-to-O Acyl-Transfer Reactions.

A bioinspired synthesis of chiral 3,4-dihydropyranones via S-to-O acyl-transfer reactions is described. Asymmetric Michael addition-lactonization reactions of β,γ-unsaturated α-keto esters with thioesters are catalyzed by proline-derived urea, providing 3,4-dihydropyranones and spiro-3,4-dihydrocoumarin-fused 3',4'-dihydropyranones in high yield (up to 94%) with excellent stereoselectivities (up to >20:1 dr, 99% ee) under catalyst loadings as low as 1 mol %.

Short Enantioselective Total Syntheses of Cheloviolenes A and B and Dendrillolide C via Convergent Fragment Coupling Using a Tertiary Carbon Radical.

The development of a convergent fragment coupling strategy for the enantioselective total syntheses of a group of rearranged spongian diterpenoids that harbor the cis-2,8-dioxabicyclo[3.3.0]octan-3-one unit is described.

Pd-Catalyzed Regioselective Asymmetric Addition Reaction of Unprotected Pyrimidines to Alkoxyallene.

Catalytic asymmetric synthesis of N-heterocyclic glycosides free of protecting and directing groups is reported. The key reaction is highlighted by the atom-efficient and regioselective addition of unprotected pyrimidines to highly functionalized alkoxyallene. Numerous acyclic and cyclic N-heterocyclic glycosides are accessed with minimal formation of organic byproducts.

Versatile Construction of 6-Substituted cis-2,8-Dioxabicyclo[3.3.0]octan-3-ones: Short Enantioselective Total Syntheses of Cheloviolenes A and B and Dendrillolide C.

A short enantioselective synthesis of 6-substituted cis-2,8-dioxabicyclo[3.3.0]octan-3-ones is described.

Role of Configuration at C6 in Catalytic Activity of l-Proline-Derived Bifunctional Organocatalysts.

l-Proline-derived chiral bifunctional (thio)urea organocatalysts epi-PTU and epi-PU were newly synthesized, and their catalytic performances were compared with their C6 epimeric catalysts PTU and PU in various Michael reactions of nitrostyrene in terms of reactivities and stereoselectivities. The experimental results indicate that a proper relative stereochemistry at C2 and C6 in l-proline-derived bifunctional organocatalysts is important for successful catalysis and that catalysts (PTU and PU) with the 2S,6R configuration are much more efficient.