Synthesis of 2-Alkylidenepyrrolidines and Pyrroles by Condensation of 1,3-Dicarbonyl Dianions with α-Azidoketones and Subsequent Intramolecular Staudinger−Aza-Wittig Reaction

Humin-sulfuric acid as a novel recoverable biocatalyst for pyrrole synthesis in water

Humin-sulfuric acid (Humin-SO3H) as a novel efficient biobased sulfonic acid was easily prepared by adding chlorosulfuric acid (ClSO3H) to Humin and characterized by potentiometric titration and FT-IR spectrum. Humin-SO3H is an eco-friendly, heterogeneous biobased, and efficient catalyst for Paal-Knorr and Clauson-Kaas pyrrole synthesis. The catalyst is easily recovered by simple filtration and has excellent turnover efficiency even after 4 cycles. Besides, due to the clearance of the biocatalyst away from the reaction media, the desired highly pure products can be achieved in high to excellent yields. Due to high water dispersibility, Humin-SO3H can be utilized as a highly efficient green catalyst for pyrrole synthesis.

A new avenue to the synthesis of highly substituted pyrroles: synthesis from N-propargylamines

Pyrroles have attracted much attention due to their potential biological activities.

Reaction of 2H-Azirine-Phosphine Oxides and -Phosphonates with Enolates Derived from β-Keto Esters

Cyclopenta[b]-pyrrole-2-phosphine oxides 4a and -phosphonates 4b,c are generated by the addition of cyclic enolates derived from ethyl 2-oxo-cyclopentanecarboxylate 2 to phosphorated 2H-azirines 1. However, the addition of enolate derived from acyclic 2-oxo-butanoate 10 to 2H-azirine phosphine oxide 1 led to vinylogous N-acyl-α-aminoalkyl phosphine oxides 12, involving the carbonyl group and the Cα of the keto ester 10. Ring closure of vinylogous derivative 12 in the presence of base afforded pyrrole-2-phosphine oxide 11. The addition of enolates derived from indenone-carboxylate 15 to 2H-azirines 1 led to the formation of functionalized N-substituted 1H-benzo[d]azepine derivatives 17.

Synthesis and Consecutive Reactions of α-Azido Ketones: A Review

This review paper covers the major synthetic approaches attempted towards the synthesis of α-azido ketones, as well as the synthetic applications/consecutive reactions of α-azido ketones.

Synthesis of 1,4-enamino ketones by [3,3]-rearrangements of dialkenylhydroxylamines

The synthesis of 1,4-enamino ketones has been achieved through the [3,3]-rearrangement of dialkenylhydroxylamines generated from the addition of N-alkenylnitrones to electron-deficient allenes. The mild conditions required for this reaction, and the simultaneous installation of a fluorenyl imine N-protecting group as a consequence of the rearrangement, avoid spontaneous cyclization of the 1,4-enamino ketones to form the corresponding pyrroles and allow for the isolation and controlled divergent functionalization of these reactive intermediates. The optimization, scope, and tolerance of the new method are discussed with demonstrations of the utility of the products for the synthesis of pyrroles, 1,4-diones, and furans.

Synthesis of polysubstituted pyrroles from sulfinimines (N-sulfinyl imines)

Polysubstituted 2-carboxylate and 2-phosphonate pyrroles are prepared by aromatization of the corresponding 3-oxo 2-carboxylate and 2-phosphonate NH-pyrrolidines using air. Reaction of electrophiles with 3-oxo pyrrolidine dianions readily introduces substituents, regioselectively at C-4 in these pyrrolidines.

Efficient Synthesis of Salicylates by Catalytic [3 + 3] Cyclizations of 1,3-Bis(silyl enol ethers) with 1,1,3,3-Tetramethoxypropane

Salicylic acid derivatives were prepared by Me3SiOTf-catalyzed [3 + 3] cyclization of 1,3-bis(silyl enol ethers) with 1,1,3,3-tetramethoxypropane.