Au-Catalyzed 5C Reaction of Type II Diene-Ynenes toward Dihydrosemibullvalenes: Reaction Development and Mechanistic Study.

We report an unexpected gold-catalyzed 5C reaction of type II diene-ynenes to synthesize dihydrosemibullvalenes, which are potential bioisosteres for drug discovery. This 5C reaction occurs through a sequence of elementary reactions of cyclopropanation/Cope rearrangement/carbon shift/cyclopropanation/C-H insertion (shortened here as the 5C reaction), supported by quantum chemistry calculations. Mechanistic studies have also been applied to answer why type-II diene-ynenes cannot access seven-membered carbocycles-embedded bridged molecules under the gold catalysis, finding that the chair-like Cope rearrangement transition state (not the traditional boat-like transition state) is the key to the change of regiochemistry.

Copper-Catalyzed Annulation-Cyanotrifluoromethylation of 1,6-Enynes Toward 1-Indanones via a Radical Process.

A new Cu(II)-catalyzed annulation-cyanotrifluoromethylation of 1,6-enynes with Togni's reagent and trimethylsilyl cyanide (TMSCN) has been established, enabling the direct construction of trifluoromethylated 1-indanones with an all-carbon quaternary center in good yields. This reaction was performed by using low-cost Cu(OTf) as the catalyst and Togni's reagent as both the radical initiator and a CF source, providing an efficient protocol for building up an 1-indanone framework with wide functional group compatibility. The reaction mechanism was proposed through a radical triggered addition/5-- cyclization/oxidation/nucleophilic cascade.

Mechanistic Study on Gold-Catalyzed Cycloisomerization of Dienediynes Involving Aliphatic C-H Functionalization and Inspiration for Developing a New Strategy to Access Polycarbocycles.

Previously, we developed a gold-catalyzed cycloisomerization of dienediynes to synthesize the fused 6,7,5-tricyclic compounds. This reaction involves aliphatic C-H functionalization under mild conditions with high regio- and diastereoselectivities. Herein, we present a combined density functional theory (DFT) and experimental study to understand its mechanism.

Silver-Catalyzed Nitration/Annulation of α-Alkynyl Arylols toward 3-Nitrated Benzofurans.

A silver-catalyzed nitration/annulation of α-alkynyl arylols is reported by using tert-butyl nitrite (TBN) as a NO radical precursor, from which a set of 3-nitrated benzofurans were synthesized with moderate to good yields. This transformation initiated by an in situ generated NO radical proceeds efficiently under mild and neutral redox conditions, which provides a new pathway toward the 3-nitrobenzofuran framework via catalytic difunctionalization of internal alkynes.

Sulfinate-Salt-Mediated Radical Relay Cyclization of Cyclic Ethers with 2-Alkynylbenzonitriles toward 3-Alkylated 1-Indenones.

A new sulfinate salt-mediated radical relay for the completion of C(sp )-H bond indenylation of cyclic ethers with readily available 2-alkynylbenzonitriles by combining silver/tert-butyl peroxide (TBHP) was established, providing a wide range of 3-alkylated 1-indenones with generally good yields. Interestingly, the current reaction system can tolerate an S-centered radical and a C-centered radical in one pot, in which the S-centered radical promotes the formation of the C-centered radical to induce a radical cascade without disturbing the reaction process. A reaction mechanism is also proposed based on control experiments.

Conformational Bias by a Removable Silyl Group: Construction of Bicyclo[n.3.1]alkenes by Ring Closing Metathesis.

Herein, we report a novel strategy based on a conformationally controlled RCM by a removable silyl group, which allows the facile synthesis of various bicyclo[n.3.1]alkenes, especially a set of highly strained bicyclo[5.

Silver-mediated radical 5-exo-dig cyclization of 2-alkynylbenzonitriles: synthesis of phosphinylated 1-indenones.

A new silver-mediated 5-exo-dig cyclization of 2-alkynylbenzonitriles with disubstituted phosphine oxide and HO has been developed. The reaction enables multiple bond-forming events including C-P, C-C and C-O bonds under atmospheric conditions, leading to the concise and direct formation of 28 examples of phosphorus-containing 1-indenones with generally good yields.

Carbanion Translocations via Intramolecular Proton Transfers: A Quantum Chemical Study.

Intramolecular proton transfers are important processes in chemical reactions and biological transformations. In particular, the translocation of reactive carbanion centers can be achieved through 1,n-proton transfer in either a direct or an assisted manner (via the protonation/deprotonation mechanism). Despite some mechanistic investigations on proton transfers within zwitterionic species, no guiding principles have been summarized for carbanion-induced intramolecular proton transfers.

Reaction of Aldehydes/Ketones with Electron-Deficient 1,3,5-Triazines Leading to Functionalized Pyrimidines as Diels-Alder/Retro-Diels-Alder Reaction Products: Reaction Development and Mechanistic Studies.

Catalytic inverse electron demand Diels-Alder (IEDDA) reactions of heterocyclic aza-dienes are rarely reported since highly reactive and electron-rich dienophiles are often found not compatible with strong acids such as Lewis acids. Herein, we disclose that TFA-catalyzed reactions of electron-deficient 1,3,5-triazines and electron-deficient aldehydes/ketones can take place. These reactions led to highly functionalized pyrimidines as products in fair to good yields.

Scalable Total Synthesis of rac-Jungermannenones B and C.

Reported is the first scalable synthesis of rac-jungermannenones B and C starting from the commercially available and inexpensive geraniol in 10 and 9 steps, respectively. The unique jungermannenone framework is rapidly assembled by an unprecedented regioselective 1,6-dienyne reductive cyclization reaction which proceeds through a vinyl radical cyclization/allylic radical isomerization mechanism. DFT calculations explain the high regioselectivity observed in the 1,6-dienyne reductive radical cyclization.

Organocatalytic Asymmetric Tandem Nazarov Cyclization/Semipinacol Rearrangement: Rapid Construction of Chiral Spiro[4.4]nonane-1,6-diones.

A novel organocatalytic asymmetric tandem Nazarov cyclization/semipinacol rearrangement reaction using "unactivated" substrates has been developed, generating a series of chiral spiro[4.4]nonane-1,6-diones in up to 96% yield and 97% enantiomeric excess. Significantly, it is the first direct example for asymmetric synthesis of cyclopentanones with four stereocenters using Nazarov cyclization.

Gold(I)-catalyzed polycyclization of linear dienediynes to seven-membered ring-containing polycycles via tandem cyclopropanation/Cope rearrangement/C-H activation.

A novel gold(I)-catalyzed polycyclization of easily prepared linear dienediynes has been developed for the construction of fused 5,7,6-tricyclic ring systems in one step with high diastereocontrol. The polycyclization, a formal [4 + 3]/C-H activation reaction, takes place through gold(I)-catalyzed intramolecular cyclopropanation of diene with diyne, Cope rearrangement of cis-alkenylalkynylcyclopropane, aliphatic C-H activation via a seven-membered-ring allene intermediate, and [1,2]-H and -G (H or OAc) shifts.