HOAc-Mediated Cyclocondensation of 2-Formylazaarenes and Cyclic Amines. Synthesis of Pyrrolo[1,2-a]azaarenes

Synthesis of sulfonyl 2-aryl-5-methylenyltetrahydropyrans

In this study, the present research describes a high-yield method for the synthesis of sulfonyl 2-aryl-5-methylenetetrahydropyrans by one-pot straightforward DABCO-promoted intramolecular Michael addition of β-sulfonyl styrene with 2-chloromethyl-1-propenol followed by intramolecular alkylation. This Baylis-Hillman-type pathway provides a highly effective stereoselective annulation by forming one carbon-oxygen bond and one carbon-carbon bond.

Divergent synthesis of two types of indolizines from pyridine-2-acetonitrile, (hetero)arylglyoxal, and TMSCN

Herein we describe the divergent synthesis of two types of indolizines via construction of the pyrrole moiety from pyridine-2-acetonitriles, arylglyoxals, and TMSCN. While one-pot three-component coupling provided 2-aryl-3-aminoindolizines via an unusual fragmentation process, a sequential two-step assembly protocol with these starting materials allowed efficient access to a wide range of new 2-acyl-3-aminoindolizines through an aldol condensation-Michael addition-cycloisomerization process. The subsequent manipulation of 2-acyl-3-aminoindolizines enabled direct access to novel polycyclic N-fused heteroaromatic skeletons.

Sequential condensation and double desulfonylative cyclopropanation of 1,2-bis(sulfonylmethyl)arenes with 3-arylacroleins: access to biscyclopropane-fused tetralins

Efficient tBuOK-mediated sequential condensation and double desulfonylative cyclopropanation of readily accessible 1,2-bis(sulfonylmethyl)arenes with 3-arylacroleins is described. This high-yielding, single-step strategy provides a variety of polysubstituted biscyclopropane-fused tetralins with six contiguous stereogenic centers via the construction of five carbon-carbon single bonds. A plausible mechanism is proposed and discussed. In the overall reaction process, water and sulfinic acid salts were generated as the byproducts.

Recent applications of quinolinium salts in the synthesis of annulated heterocycles

Quinoline derivatives are frequently found in natural products and biologically active compounds, however, construction of quinoline fused polyheterocycles is the challenging goal in synthetic organic chemistry. In this regard, quinolinium salts meet the demand to a great level, as they can be synthesized readily and employed effectively for the rapid construction of condensed heterocyclic core. The present review focuses on recent (2015-2021) applications of different quinolinium salts that react with suitable partners to access diverse annulated products. Most of the reactions discussed here involve easily available starting materials, operationally simple, high atom efficiency and environmentally benign. Mechanistic aspects of representative transformations have also been highlighted for better understanding of reaction pathway.

Tandem cyclocondensation of 1,3-bis-sulfonylpropan-2-ones with arylaldehydes. One-pot synthesis of tris-sulfonyl 3-arylphenols

One-pot tandem piperidinium acetate-mediated cyclocondensation of 1,3-bis-sulfonylpropan-2-ones with arylaldehydes generates tris-sulfonyl 3-arylphenols in moderate to good yields in refluxing toluene under easy-operational reaction conditions.

Condensation-Based Methods for the C-H Bond Functionalization of Amines

This review aims to provide a comprehensive overview of condensation-based methods for the C-H bond functionalization of amines that feature azomethine ylides as key intermediates. These transformations are typically redox-neutral and share common attributes with classic name reactions such as the Strecker, Mannich, Friedel-Crafts, Pictet-Spengler, and Kabachnik-Fields reaction, while incorporating a redox-isomerization step. This approach provides an ideal platform to rapidly transform simple starting materials into complex amines.

Calcium-Catalyzed Stereoselective Tandem [4+2] and [3+2] Annulation Reaction for the Synthesis of Dihydropyrrolo[1,2-a]quinolines

Calcium-catalyzed highly facile one-pot, A⁴ annulation of aldehyde, amine, alkene, and alkyne to form fused 4,5-dihydropyrrolo[1,2-a]quinolines with exclusive syn diastereoselectivity is reported. This selectivity arises from an inverse electron demand [4+2] aza-Diels-Alder cycloaddition, and the adduct further undergoes a formal [3+2] cyclization with activated alkynes. This diversity-oriented protocol is highly general and furnishes the dihydropyrrolo[1,2-a]quinoline derivatives with a broad substrate scope in good to excellent yields.