Synthesis of functionalized pyrroles via catalyst- and solvent-free sequential three-component enamine-azoene annulation

A new and efficient synthesis of polysubstituted pyrroles by a sequential one-pot three-component reaction between primary aliphatic amines, active methylene compounds, and 1,2-diaza-1,3-dienes (DDs) is reported. The reactions were performed without catalyst and under solvent-free conditions with complete control of pathway selectivity. Notably, the ready availability of the starting materials and the high level of practicability of the reaction and work up make this approach an attractive complementary method for access to unknown polysubstituted pyrroles.     

Conjugated azoalkenes. Part V. Facile synthesis of new 1-aroylamino-3-sulfonylpyrroles by reaction of aroylazoalkenes with 1,3-ketosulfones

The easy one-pot synthesis of the interesting 1-aroylamino-3-sulfonylpyrroles by reaction of some aroylazo-alkenes with 1,3-ketosulfones is reported.     

Mass spectrometric characterization of substituted 2-thiazolin-4-one derivatives

Electron ionization mass spectrometry was used for the structural characterization of substituted 2-thiazolin-4-one derivatives in the gas phase. The compounds follow common fragmentation pathways, producing ions whose abundances are dependent on the chemical nature of the substituent at position 2. Collision-induced dissociation tandem mass spectrometric experiments, carried out on both molecular ions and fragment ions produced in the source, allowed the elucidation of gas-phase decompositions. The presence of tautomeric forms is suggested for some ionic species. Rapid identification of a primary or secondary amine moiety at position 2 of the thiazoline ring can be achieved by the detection of characteristic fragmentations occurring both in the ion source and under the collision-induced dissociation regime.     

Simple construction of fused and spiro nitrogen/sulfur containing heterocycles by addition of thioamides or thioureas on cycloalkenyl-diazenes: examples of click chemistry

New 1-cycloalkenyl-1-diazenes have been obtained in good yields from cyclic β-ketoesters and hydrazine derivatives. They furnished new cycloalkyl[d][1,3]thiazolines with thioamides or new spirocycloalkyl-thiazolinones with thioureas. Moreover they gave, with imidazolidine-2-thione and tetrahydropyrimidine-2-thione, new and interesting spiro[cycloalkyl-1,2′-imidazo[2,1-b][1,3]thiazole] or spiro[cycloalkyl-1,2′-[1,3]thiazolo[3,2-a]pyrimidine] derivatives, respectively. Cycloalkyl[d][1,3]thiazolines were useful for the further preparation of unknown thia-triaza-tricyclo derivatives. Novel hexahydro-1,3-benzothiazoles have been achieved by reaction of N,N′-dialkylthioureas on N-1-phenyl-2-(1-cyclohexenyl)-1-diazene-1-carboxyamide. The acidic hydrolysis of spirocycloalkyl-thiazolinones produced 2-imino-5-(ω-carboxyalkyl)-4-thiazolidinones.     

Efficient synthesis and environmentally friendly reactions of PEG-supported 1,2-diaza-1,3-butadiene

[reaction: see text] Here, we report the protocol for the preparation of new poly(ethylene glycol)-supported 1,2-diaza-1,3-butadiene. In addition, we discuss an application of this supported reagent in an efficient and environmentally friendly one-pot synthesis of 2-thiazol-4-one derivatives by reaction with thioamides.     

Straightforward entry into 5-hydroxy-1-aminopyrrolines and the corresponding pyrroles from 1,2-diaza-1,3-butadienes

The synthesis of 5-hydroxy-1-aminopyrroline-3-carboxylic acid derivatives and 5-unsubstituted-1-aminopyrrole-3-carboxylic acid derivatives from 1,2-diaza-1,3-butadienes and aldehydes is presented. These domino reactions offer the advantage of executing multistep transformation without intermediate workup procedures. The stereoselectivity of ring closure to 5-hydroxy-1-aminopyrroline-3-carboxylic acid derivatives and phenyl transposition to 2,3-diphenyl-1-aminopyrrole-3-carboxylic acid derivatives are also studied.     

From targeted aza-Michael addition to linked azaheterocyclic scaffolds

A straightforward method for the synthesis of spaced, phenyl-linked bis(thiohydantoin) derivatives and (thio)hydantoins spiro-fused to pyrroline ring has been developed. All the synthetic strategies here presented rely on initial aza-Michael addition followed by acylation/regioselective ring-closure step involving DD, primary amine and iso(thio)cyanate in a 3-CR providing 1,3,5-trisubstituted (thio)hydantoins. The choice of opportune acyclic reagents in the sequential 3-CR followed by 1,4-nucleophilic addition/intramolecular ring closing and 1,3-dipolar cycloaddition permits a number of C–N and C–C formation that realizes different kind of linkage between several pharmacophores.     

Divergent base-induced reactivity of cycloalkenyl-1-diazenes

The different base-promoted regioselectivities of the ring closure processes in the reactions between cycloalkenyl-1-diazenes and β-ketoesters are investigated. Under the appropriate conditions it is possible to turn the synthesis towards cycloalkenyliden-pyrroles or functionalized 3-hydroxy-hydrocinnolines. The aromatization procedure of the heteroring counterpart of the 3-hydroxy-hydrocinnolines is also reported.     

Electrophilic Reactivities of 1,2‐Diaza‐1,3‐dienes

The kinetics of the reactions of 1,2‐diaza‐1,3‐dienes 1 with acceptor‐substituted carbanions 2 have been studied at 20 °C. The reactions follow a second‐order rate law, and can be described by the linear free energy relationship log k(20 °C)=s(N+E) [Eq. (1)]. With Equation (1) and the known nucleophile‐specific parameters N and s for the carbanions, the electrophilicity parameters E of the 1,2‐diaza‐1,3‐dienes 1 were determined. With E parameters in the range of ?13.3 to ?15.4, the electrophilic reactivities of 1 a–d are comparable to those of benzylidenemalononitriles, 2‐benzylideneindan‐1,3‐diones, and benzylidenebarbituric acids. The experimental second‐order rate constants for the reactions of 1 a – d with amines 3 and triarylphosphines 4 agreed with those calculated from E, N, and s, indicating the applicability of the linear free energy relationship [Eq. (1)] for predicting potential nucleophilic reaction partners of 1,2‐diaza‐1,3‐dienes 1 . Enamines 5 react up to 10² to 10³ times faster with compounds 1 than predicted by Equation (1), indicating a change of mechanism, which becomes obvious in the reactions of 1 with enol ethers.     

Tetrabromo hydrogenated cardanol: Efficient and renewable brominating agent

2,4,4,6-Tetrabromo-3-n-pentadecyl-2,5-cyclohexadienone (TBPCO) has been synthesized and used as a new efficient, convenient, and environmentally friendly brominating agent.