Formal Synthesis of Amipurimycin and 4'-Deoxymiharamycin B by Way of Sequential Asymmetric Metal Catalysis.

Herein, we describe a highly efficient formal synthesis of nucleoside antibiotics amipurimycin and 4'-deoxymiharamycin B. A signature event is highlighted by the sequential metal catalysis combining (i) Pd-catalyzed asymmetric hydroalkoxylation of an alkoxyallene; (ii) Ru-catalyzed enyne-methathesis, and (iii) Os-catalyzed dihydroxylation. Remarkably, this atom-efficient sequence allows for the construction of a 3'-branched pyranose core structure in only four steps from readily available Garner's aldehyde.

Formal Synthesis of (+)-Sinefungin by Way of Sequential Asymmetric Metal Catalysis.

Here, we report a de novo approach toward (+)-sinefungin, a potent inhibitor of the physiological methyl transfer process. A key feature is represented by the sequential metal catalysis combining Pd-catalyzed hydroalkoxylation and ring-rearrangement metathesis. The unique advantage of the method is highlighted by the unprecedented complete control of the C6 stereocenter.

Total Synthesis of the Purported Structure of Branched Resin Glycosides Merremoside G and H2.

The first total synthesis of the purported structure of branched resin glycosides merremoside G and H2 is accomplished. A signature step is represented by the sequential transition-metal-catalyzed coupling of stable trisaccharide homoallylic alcohol and monosaccharide alkoxyallene to afford the pentasaccharide skeleton. This de novo strategy is conducted under mild conditions with no need of preactivation. In addition, it allows for efficient preparation of the target compounds in combination with late-stage functionalization.

Synthesis of the Tetrasaccharide Glycone Part of Tetrocarcin A.

A de novo synthesis of the tetrasaccharide fragment of tetrocarcin A is described. The key feature of this approach is highlighted by the regio- and diastereoselective Pd-catalyzed hydroalkoxylation of ene-alkoxyallenes with an unprotected l-digitoxose glycoside. The subsequent reaction with digitoxal in combination with chemoselective hydrogenation generated the target molecule.

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. The synthetic utility of this reaction was demonstrated by the short synthesis of the tetrahydropyran fragment of the anticancer natural product mucocin.

Sequential Metal Catalysis towards 7-Oxostaurosporine and Its Non-Natural Septanose Analogue.

We report sequential metal catalysis towards indolocarbazole glycosides. The signature event is highlighted by i) Pd0 -catalyzed addition of indolocarbazole to alkoxyallene combined with ring-closing-metathesis; ii) Ru-catalyzed chemoselective olefin migration; iii) PdII -catalyzed oxidative cyclization to build the bicyclic core structure of the target compounds. This approach gave access to both natural pyranose- and non-natural septanose glycosides. A short formal synthesis of 7-oxostaurosporine was achieved via this strategy.

Generation of N-H Imines from α-Azidocarboxylic Acids through Ru-Catalyzed Decarboxylation.

A new method for the synthesis of N-H imines from α-azidocarboxylic acids was developed, which proceeds through decarboxylative C-C bond cleavage catalyzed by a commercial diruthenium complex ([CpRu(CO)2]2) under visible light irradiation at room temperature within several minutes. The reactive products undergo condensation, which forms cyclic trimers (2,4,6-trialkylhexahydro-1,3,5-triazines) or linear N,N'-bis(arylmethylidene)arylmethanediamines in quantitative yields. Alternatively, the N-H imines can be trapped with benzylamine and 2-(aminomethyl)aniline, providing stable N-benylimines and tetrahydroquinazolines, respectively. Subsequent oxidation of tetrahydroquinazolines produced quinazolines.

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

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

Synthetic Study toward Saccharomicin Based upon Asymmetric Metal Catalysis.

Here, we report a de novo metal-catalyzed approach toward the stereoselective glycosidic bond formation in saccharomicin. The signature step is highlighted by the Pd-catalyzed asymmetric coupling of ene-alkoxyallenes and highly functionalized alcohol substrates. The reaction showed high chemo-, regio-, and ligand-driven diastereoselectivity. In combination with the ring-closing metathesis and late-stage functionalization, this method led to highly efficient synthesis of saccharosamine-rhamnose and rhamnose-fucose fragments.

Convergent Synthesis of Tetrasaccharide Fragment of Cervimycin K.

A new synthetic approach toward oligosaccharides consisting only of 2,3,6-trideoxypyranoglycosides is reported. The key feature is highlighted by the convergent approach that allows the introduction of the aglycon moiety in the late stage of the synthesis. As an illustrative example, the tetrasaccharide portion of cervimycin K was prepared as cyclohexyl glycoside.

Catalytic Asymmetric Synthesis of Hexahydro-furofuran-3-ol and Its Pyran Derivatives.

The catalytic asymmetric synthesis of hexahydro-furofuran-3-ol, a key fragment of HIV protease inhibitors, is reported. A signature event is represented by the sequential metal catalysis that combines the Pd-catalyzed asymmetric hydroalkoxylation of ene-alkoxyallene and ring-closing metathesis (RCM). Notably, this unprecedented and highly chemoselective approach allows for a unified access to pyranofuranol and furopyranol derivatives.

Concurrent Formation of N-H Imines and Carbonyl Compounds by Ruthenium-Catalyzed C-C Bond Cleavage of ß-Hydroxy Azides.

A commercial cyclopentadienylrutenium dicarbonyl dimer ([CpRu(CO)2]2) efficiently catalyzes the formation of N-H imines and carbonyl compounds simultaneously from ß-hydroxy azides via C-C bond cleavage under visible light. Density functional theory calculations for the cleavage reaction support the mechanism involving chelation of alkoxy azide species and liberation of nitrogen as the driving force. The synthetic utility of the reaction was demonstrated by a new amine synthesis promoted by chemoselective allylation of imine and synthesis of isoquinoline.

Ruthenium-Catalyzed Regioselective Olefin Migration of Dihydropyran Acetals: A De Novo Strategy toward ß-2,6-Dideoxypyranoglycosides.

Here, we report a de novo synthetic strategy toward ß-2,6-dideoxypyranoglycosides. The key event is the ruthenium-catalyzed regioselective olefin migration of dihydropyran allylic acetals to homoallylic acetals. In combination with other metal-catalyzed reactions, this new protocol led to the synthesis of ß-2,6-dideoxypyranoglycosides in a highly efficient manner. Using this sequential metal catalysis, various mono-, di-, and trisaccharide forms of ß-2,6-dideoxypyranoglycosides were prepared.

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.

Synthesis of Deoxyaminosugar Cyclohexyl-l-callipeltose and Its Diastereomer Using Pd-Catalyzed Asymmetric Hydroalkoxylation.

Cyclohexyl-l-callipeltose, an aminodeoxysugar subunit of Callipeltoside A, was synthesized in six steps and 40% overall yield from readily available (S)-4-methylpent-4-en-2-ol and cyclohexyloxyallene. The signature step is represented by Pd-catalyzed asymmetric intermolecular hydroalkoxylation that generates the key dihydropyran intermediate upon combination with the ring-closing metathesis reaction. Notably, an unnatural diastereomer of the target compound could also be obtained with comparable efficiency simply by using the enantiomeric ligand.

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.

Palladium-Catalyzed Asymmetric Nitrogen-Selective Addition Reaction of Indoles to Alkoxyallenes.

A new palladium-catalyzed asymmetric addition reaction of indoles to alkoxyallenes is reported. Remarkably, the reaction showed complete regioselectivity toward the nitrogen. A new mechanism distinct from that of conventional π-allyl chemistry is proposed to explain this unique selectivity. The utility of the reaction is demonstrated by highly efficient and flexible synthesis of N-glycosylindoles.

Ru-Catalyzed Chemoselective Olefin Migration Reaction of Cyclic Allylic Acetals to Enol Acetals.

A Ru-catalyzed olefin migration reaction of chiral cyclic allylic acetal is reported. The reaction generates cyclic enol acetal in a highly chemoselective manner. A variety of O,O- and N,O-acetals participated in the reaction with conservation of the stereochemical integrity of the acetal moiety. The utility of the reaction was demonstrated by the short and protective group-free syntheses of (L)-deoxyribonucleoside and ß-amicetose glycoside.

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. The key bond disconnection relies on a late-stage fragment coupling between a tertiary carbon radical and an electron-deficient alkene to unite two ring systems and form two new stereocenters, one of which is quaternary, in a stereoselective and efficient manner. This strategy is applied toward scalable 14-15 step syntheses of three rearranged spongian diterpenoids, cheloviolenes A and B, and dendrillolide C.

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. The synthetic utility of the reaction is demonstrated by the first catalytic asymmetric synthesis of anticancer pharmaceutical (-)-Tegafur and stereoselective synthesis of an oxepane nucleoside derivative.