Divergent synthesis of N-heterocyclic 1,6-enynes through a zinc-catalyzed decarboxylative A3 reaction

Rapid Access to Divergent Fused Polycycles Via One-Pot A3 Coupling and Intramolecular Diels-Alder Reaction

Divergent nitrogen-containing fused polycyclic ring systems are constructed from simple starting materials via a one-pot aldehyde-alkyne-amine (A3) coupling and intramolecular Diels-Alder reaction. This domino reaction directly furnishes linear 5/5/5 and 5/5/6, or nonlinear 5/5/6/5, polycyclic rings containing an oxa-bridged fused 5/5 bicycle and a 1,6-enyne substructure. One-step derivation of the oxa-bridged 5/5 bicycle leads to a polyfunctionalized 5/5 bicycle with tetrahydrofuran fused back-to-back to pyrroline or a 6/5 bicycle with the hexahydro-1H-isoindole structure, while cycloisomerizing the enyne substructure adds an extra fused 5-membered ring to afford functionalized linear 5/5/5/5 or 5/5/5/5/5 fused ring systems from selected substrates. In addition, the one-pot product can be designed so that the alkyne moiety is hydroalkoxylated to form an additional heterocyle in a linear 5/5/5/6 or nonlinear 5/5/6/5/5 ring system. This diversity-oriented synthetic approach thus allows rapid access to an under-explored structural space for discovery of new biological or non-biological activities or functions.

Synthesis of bridgehead-azacycles via dual C-N/C-C annulation of α-amino acids, aminals and maleimides

The synthesis of various bridged azacyclic adducts has recently become a reemerging topic due to their bioactive and natural product mimic profiles. Accordingly, herein, we report a method for easy access to succinamide-bridged azacyclic derivatives through the metal-free polarization-controlled dual C-N/C-C annulation of readily available α-amino acids, 2-amino benzaldehydes or pyrrole/indole-2-aldehyde and maleimide substrates. This cascade features a rare dipolarophile-induced diastereo-selective amidative annulation, followed by 3 + 2 cycloaddition as key steps.

SmI2‑Mediated Intermolecular Addition-Elimination of Piperidine and Pyrrolidine N-α-Radicals with Arylacetylene Sulfones

An efficient approach to access α-arylacetylene substituted pyrrolidine and piperidine derivatives has been developed through a samarium diiodide mediated addition-elimination process of pyrrolidine and piperidine N-α-radicals with arylacetylene sulfones.

Synthesis of nitrogen-tethered 1,6-enynes through CuI/TFA catalysis

A new cascade process of the TFA-promoted Pictet–Spengler reaction and Cu-catalyzed intermolecular hydride transfer/alkynylation of an amine, formaldehyde solution, and an alkyne has been developed.

C-H bond cleavage-enabled aerobic ring-opening reaction of in situ formed 2-aminobenzofuran-3(2H)-ones

A C-H bond cleavage-enabled aerobic ring-opening reaction of 2-aminobenzofuran-3(2H)-ones formed in situ by hemiacetals with a variety of amines is reported. This simple one-pot reaction provides an alternative approach to obtain o-hydroxyaryl glyoxylamides in excellent yields of up to 97%. Alkylamines react with hemiacetals via a catalyst-free dehydration condensation to generate 2-aminobenzofuran-3(2H)-ones. The in situ formed semicyclic N,O-acetals undergo the same amine-initiated C-H bond hydroxylation in air under mild conditions to afford ring-opening products. Similarly, arylamines were investigated as substrates for a two-step tandem process involving a DPP-catalyzed condensation followed by a Et₂NH-mediated C-H hydroxylation. Unlike the previously reported functionalization of N,O-acetals via a C-O or C-N cleavage, the aerobic oxidative C-H hydroxylation in this reaction, which is promoted by using stoichiometric amounts of alkylamines as both a Lewis base and a reductant at room temperature under atmospheric air, proceeds via α-carbonyl-stabilized carbanion intermediates from the C-H cleavage of N,O-acetals.

Cu(OTf)2 catalyzed Ugi-type reaction of N,O-acetals with isocyanides for the synthesis of pyrrolidinyl and piperidinyl 2-carboxamides

The Cu(OTf)₂ catalyzed Ugi-type reactions of N,O-acetals with isocyanides have been described for the synthesis of pyrrolidinyl and piperidinyl 2-carboxamides. 4-Hydroxy-5-substituted-prolinamides can be obtained in high diastereoselectivities (2,4-cis/trans > 19 : 1) and a stereoselective model was proposed for 2,4-cis selectivity. Moreover, 4-F-VH 032, a novel analog of the VHL ligand, was conveniently obtained by utilizing the present method.

A One-Pot Approach to 2-Substituted-2-(Dimethoxyphosphoryl)-Pyrrolidines from Substituted tert-Butyl 4-Oxobutylcarbamates and Trimethyl Phosphite

A novel approach to 2-substituted-2-(dimethoxyphosphoryl)-pyrrolidines 7a-7o and 9a-9r has been developed, which features a TMSOTf-mediated one-pot intramolecular cyclization and phosphonylation of substituted tert-butyl 4-oxobutylcarbamates. The major advantages of this method include simple operation under mild reaction conditions, the use of cheap Lewis acid, and good to excellent yields with high diastereoselectivities (dr up to 99:1).

α-Hydroxy acid as an aldehyde surrogate: metal-free synthesis of pyrrolo[1,2-a]quinoxalines, quinazolinones, and other N-heterocycles via decarboxylative oxidative annulation reaction

A metal-free and efficient procedure for the synthesis of pyrrolo[1,2-a]quinoxalines, quinazolinones, and indolo[1,2-a]quinoxaline has been developed. The key features of our method include the in situ generation of aldehyde from α-hydroxy acid in the presence of TBHP (tert-butyl hydrogen peroxide), and further condensation with various amines, followed by intramolecular cyclization and subsequent oxidation to afford the corresponding quinoxalines, quinazolinones derivatives in moderate to high yields.