Rhodium(I)-Catalyzed C−C Bond Activation of Siloxyvinylcyclopropanes with Diazoesters

Divergent Reactions of α-Diazo 1,3-Dicarbonyl Compounds with Allylic Carbonates Involving Ketene versus Carbene Intermediates Enabled by Cooperative Rh(II)/Pd(0) Dual Catalysis

A cooperative Rh(II)/Pd(0) dual-catalysis strategy that enabled divergent reactions of α-diazo 1,3-dicarbonyl compounds with allylic carbonates involving ketene versus carbene intermediates is described. The efficient synthesis of α-quaternary allylated β-keto-esters was accomplished by the Rh(II)/Pd(0) dual-catalysis allylic alkylation of α-diazo 1,3-dicarbonyl compounds. Alternatively, an unprecedented (1+4) annulation of α-diazo 1,3-dicarbonyl compounds with 2-(hydroxymethyl)allyl carbonates via Rh(II)/Pd(0) dual catalysis was also successfully developed, affording a wide variety of α-quaternary tetrahydrofurans in good to high yields.

Rhodium(I)-catalyzed C-S bond formation via enantioselective carbenoid S-H insertion: catalytic asymmetric synthesis of α-thioesters

Asymmetric construction of C-S bond through transition-metal catalysis is a challenging subject. By using chiral diene as ligand, we have developed the first rhodium(I)-catalyzed asymmetric carbene insertion approach for C-S...

Experimental and Computational Studies on Rh(I)-Catalyzed Reaction of Siloxyvinylcyclopropanes and Diazoesters

The Rh(I)-catalyzed reaction of siloxyvinylcyclopropanes and diazoesters leads to the formation of siloxyvinylcyclobutane and 1,4-diene derivatives. With [Rh(cod)Cl]₂ as the catalyst, the formation of 1,4-diene was favored over the formation of siloxyvinylcyclobutane. By changing the catalyst to [Rh(cod)₂OTf], siloxyvinylcyclobutane derivatives are formed with excellent chemoselectivities and in moderate to good yields. The alkene products are also obtained as single E configured isomers. A detailed mechanism for this transformation is proposed on the basis of mechanistic experiments and DFT calculations. The effect of catalysts on the chemoselectivity of these reactions is also examined computationally.

Convergent Synthesis of Dihydropyrans from Catalytic Three-Component Reactions of Vinylcyclopropanes, Diazoesters, and Diphenyl Sulfoxide

A novel Rh(I)/La(III) cocatalytic three-component reaction of vinylcyclopropanes, diazoesters, and diphenyl sulfoxide has been developed. The reaction gives polysubstituted dihydropyrans as the reaction products. Mechanistic studies indicate that isomerization of vinylcyclopropanes gives conjugated dienes, which then undergo [4 + 2]-cycloaddition with vicinal tricarbonyl compounds generated by oxygen atom transfer from diphenyl sulfoxide to diazoesters.

Palladium-catalyzed oxidative borylation of conjugated enynones through carbene migratory insertion: synthesis of furyl-substituted alkenylboronates

A new method for the synthesis of furyl-substituted alkenylboronates has been developed by palladium-catalyzed oxidative borylation reaction of conjugated enynones.

Z-Selective iridium-catalyzed cross-coupling of allylic carbonates and α-diazo esters

A well-defined Ir-allyl complex catalyzes the Z-selective cross-coupling of allyl carbonates with α-aryl diazo esters. The process overrides the large thermodynamic preference for E-products typically observed in metal-mediated coupling reactions to enable the synthesis of Z,E-dieneoates in good yield with selectivities consistently approaching or greater than 90 : 10. This transformation represents the first productive merger of Ir-carbene and Ir-allyl species, which are commonly encountered intermediates in allylation and cyclopropanation/E-H insertion catalysis. Potentially reactive functional groups (aryl halides, ketones, nitriles, olefins, amines) are tolerated owing to the mildness of reaction conditions. Kinetic analysis of the reaction suggests oxidative addition of the allyl carbonate to an Ir-species is rate-determining. Mechanistic studies uncovered a pathway for catalyst activation mediated by NEt3.

Iridium-catalyzed [4 + 2] annulation of 1-arylindazolones with α-diazo carbonyl compounds: access to indazolone-fused cinnolines

An Ir-catalyzed tandem strategy for the synthesis of indazolone-fused cinnolines by [4 + 2] annulation of 1-arylindazolones with α-diazo carbonyl compounds.

Copper(ii)-mediated, carbon degradation-based amidation of phenylacetic acids toward N-substituted benzamides

The carbon degradation-based amidation of phenylacetic acids with aryl amides has been realized in the presence of Cu(OAc)₂, which provides a practical route in the synthesis of N-aryl secondary benzamides.

Transition-Metal-Catalyzed Cross-Couplings through Carbene Migratory Insertion

Transition-metal-catalyzed cross-coupling reactions have been well-established as indispensable tools in modern organic synthesis. One of the major research goals in cross-coupling area is expanding the scope of the coupling partners. In the past decade, diazo compounds (or their precursors N-tosylhydrazones) have emerged as nucleophilic cross-coupling partners in C-C single bond or C═C double bond formations in transition-metal-catalyzed reactions. This type of coupling reaction involves the following general steps. First, the organometallic species is generated by various processes, including oxidative addition, transmetalation, cyclization, C-C bond cleavage, and C-H bond activation. Subsequently, the organometallic species reacts with the diazo substrate to generate metal carbene intermediate, which undergoes rapid migratory insertion to form a C-C bond. The new organometallic species generated from migratory insertion may undergo various transformations. This type of carbene-based coupling has proven to be general: various transition metals including Pd, Cu, Rh, Ni, Co, and Ir are effective catalysts; the scope of the reaction has also been extended to substrates other than diazo compounds; and various cascade processes have also been devised based on the carbene migratory insertion. This review will summarize the achievements made in this field since 2001.

K2CO3-Mediated Cyclization and Rearrangement of γ,δ-Alkynyl Oximes To Form Pyridols

A novel K₂CO₃-mediated cyclization and rearrangement of γ,δ-alkynyl oximes for the synthesis of pyridols is described. The process accomplishes an efficient [1,3] rearrangement of the O-vinyl oxime intermediate which is in situ generated from the intramolecular nucleophilic addition of γ,δ-alkynyl oximes. The reaction employs readily accessible starting materials, tolerates a wide range of functional groups, and gives a variety of synthetically challenging pyridols in good yields.

Highly Stereoselective Gold-Catalyzed Coupling of Diazo Reagents and Fluorinated Enol Silyl Ethers to Tetrasubstituted Alkenes

We report a highly stereoselective synthesis of all-carbon or fluorinated tetrasubstituted alkenes from diazo reagents and fluorinated enol silyl ethers, using C-F bond as a synthetic handle. Cationic Au^I catalysis plays a key role in this reaction. Remarkable fluorine effects on the reactivity and selectivity was also observed.