Stereoselective Synthesis of Highly Substituted Tetrahydrofurans through Diverted Carbene OH Insertion Reaction

Unveiling the mechanisms and secrets of chemoselectivities in Au(i)-catalyzed diazo-based couplings with aryl unsaturated aliphatic alcohols

The mechanisms and origins of the unsaturated-aliphatic-alcohols-modulated chemoselectivity of Au-catalyzed carbene transfers from diazo compounds are disclosed by DFT studies.

Cycloaddition reactions of enoldiazo compounds

Enoldiazo esters and amides have proven to be versatile reagents for cycloaddition reactions that allow highly efficient construction of various carbocycles and heterocycles. Their versatility is exemplified by (1) [2+n]-cycloadditions (n = 3, 4) by the enol silyl ether units of enoldiazo compounds with retention of the diazo functionality to furnish α-cyclic-α-diazo compounds that are themselves subject to further transformations of the diazo functional group; (2) [3+n]-cycloadditions (n = 1-5) by metallo-enolcarbenes formed by catalytic dinitrogen extrusion from enoldiazo compounds; (3) [2+n]-cycloadditions (n = 3, 4) by donor-acceptor cyclopropenes generated in situ from enoldiazo compounds that produce cyclopropane-fused ring systems. The role of dirhodium(ii) and the emergence of copper(i) catalysts are described, as are the different outcomes of reactions initiated with these catalysts. This comprehensive review on cycloaddition reactions of enoldiazo compounds, with emphasis on methodology development, mechanistic insight, and catalyst-controlled chemodivergence, aims to provide inspiration for future discoveries in the field and to catalyze the application of enoldiazo reagents by the wider synthetic community.

Palladium-Catalyzed Cascade Wacker/Allylation Sequence with Allylic Alcohols Leading to Allylated Dihydropyrones

We describe a cascade Wacker/allylation sequence of β-hydroxy ynones by directly using simple allylic alcohols. This palladium(II)-catalyzed reaction occurs under mild conditions (0 °C to room temperature) and provides a new and efficient synthetic method for the preparation of allylated dihydropyrones. The regiochemical outcomes are consistent with a reaction pathway that includes an insertion/β-OH elimination sequence to form the allylic moiety. A remarkable changeover from allyl to formylethyl products occurs under the simple action of LiBr.

Synthesis of seven-membered heterocycles via copper-catalyzed cross-coupling of terminal alkynes with diazo compounds and sequential Michael addition

A novel approach to synthesize seven-membered heterocycles is established by reacting amide tethered terminal alkynes with aryl diazoacetates in a one-pot reaction.

A controlled selective synthesis of dihydropyrans through tandem reaction of alkynes with diazo compounds

A controlled synthesis of dihydropyrans via sequential reaction of allenoate formation and intramolecular oxo-Michael addition has been achieved.

Gold-Catalyzed Formal [4+1]/[4+3] Cycloadditions of Diazo Esters with Triazines

Reported herein is the unprecedented gold-catalyzed formal [4+1]/[4+3] cycloadditions of diazo esters with hexahydro-1,3,4-triazines, thus providing five- and seven-membered heterocycles in moderate to high yields under mild reaction conditions. These reactions feature the use of a gold complex to accomplish the diverse annulations and the first example of the involvement of a gold metallo-enolcarbene in a cycloaddition. It is also the first utilization of stable triazines as formal dipolar adducts in the carbene-involved cycloadditions. Mechanistic investigations reveal that the triazines reacted directly, rather than as formaldimine precursors, in the reaction process.

Stereoselective Synthesis of Functionalized Pyrrolidines by the Diverted N-H Insertion Reaction of Metallocarbenes with β-Aminoketone Derivatives

A highly stereoselective route to functionalized pyrrolidines by the metal-catalyzed diverted N-H insertion of a range of diazocarbonyl compounds with β-aminoketone derivatives is described. A number of catalysts (rhodium(II) carboxylate dimers, copper(I) triflate, and an iron(III) porphyrin) are shown to promote the process under mild conditions to give a wide range of highly substituted proline derivatives. The reaction starts as a metallocarbene N-H insertion but is diverted by an intermolecular aldol reaction.

Synthesis of Chiral Tetrahydrofurans via Catalytic Asymmetric [3 + 2] Cycloaddition of Heterosubstituted Alkenes with Oxiranes

An efficient diastereo- and enantioselective [3 + 2] cycloaddition of heterosubstituted alkenes with oxiranes via selective C-C bond cleavage of epoxides has been developed. The reaction was catalyzed by a chiral N,N'-dioxide/Ni(II) catalyst, and a variety of chiral highly substituted tetrahydrofurans were obtained in up to 99% yield, 92/8 dr, and 99% ee.

Protecting-Group-Free Total Synthesis of (-)-Jiadifenolide: Development of a [4 + 1] Annulation toward Multisubstituted Tetrahydrofurans

A concise, protecting-group-free total synthesis of (-)-jiadifenolide, a synthetically challenging seco-prezizaane sesquiterpene with potent neurotrophic activity, is reported. The convergent route features a SmI2/H2O-mediated stereoselective reductive cyclization, an unprecedented formal [4 + 1] annulative tetrahydrofuran-forming reaction and programmed redox manipulations. The newly developed annulation of β-hydroxy aldehydes or ketones with lithium trimethylsilyldiazomethane provides access to a diverse array of multisubstituted tetrahydrofurans. The synthetic jiadifenolide exhibited weak cytotoxicity against five human cancer cell lines.