Efficient synthesis of 5,6,7-trisubstituted 1H-pyrrolizines

Transition-Metal-Free, Atom- and Step-Economic Synthesis of Aminoketopyrrolizines from Benzylamine, Acylethynylpyrroles, and Acylacetylenes

A concise, atom-economic strategy for the synthesis of pyrrolizines with amino and keto substituents has been developed. It includes the following key steps: (i) the base-catalyzed (K₃PO₄/DMSO) addition of a benzylamine to 2-acylethynylpyrroles and (ii) noncatalyzed addition of enaminones obtained to the triple bond of acylacetylenes followed by intramolecular cyclization of the intermediate pentadiendiones thus formed to the target 1-(benzylamino)-2-acyl-3-methylenoacylpyrrolizines.

A synthesis of functionalized dihydro-1Η-pyrrolizines and spiropyrrolizines via [2 + 3] cycloaddition reactions

A one-pot synthesis of dihydro-1H-pyrrolizine derivatives via [Formula: see text] cycloaddition reaction of azomethine ylides, prepared in situ from proline and ninhydrin, with dialkyl acetylenedicarboxylates, in alcohols, is described. When sarcosine was used instead of proline, functionalized spiropyrrolizines were obtained. Under these conditions, alkyl propiolates produced stable spirans.

An integrated overview on pyrrolizines as potential anti-inflammatory, analgesic and antipyretic agents

Despite the existence of huge number of NSAIDs, the quest for safer drugs is still in the focus of several drug discovery programs. Pyrrolizine heterocyclic system is among the privileged scaffolds utilized in this regard. At least one of these pyrrolizines, ketorolac, has reached the market. The current review represents a collective effort to highlight the reported pyrrolizines with anti-inflammatory and analgesic potential and categorize them into eight different classes. Furthermore, the various synthetic approaches, structure-activity relationship as well as metabolic pathways have been discussed. Taken together, this review sets a base for researchers to design and synthesize novel pyrrolizine-based libraries for further development into safer and efficient anti-inflammatory and analgesic agents.

Access to pyrrole-based heterocyclic compounds via addition of pyrrole to C=C and C=N bonds

A series of metal triflate-catalyzed addition reactions of pyrrole to C=C and C=N bonds have been investigated to access pyrrole-based heterocyclic compounds. The addition of pyrrole to different α,β-unsaturated compounds or N-tosyl imines afforded suitable structures for the construction of [5-5] bicyclic systems or porphyrins, respectively. Intramolecular cyclization reactions were applied for the synthesis of pyrrolizine derivatives. In the other reaction mode, intermolecular cyclization reactions gave A4- and trans-A2B2-meso-substituted porphyrins under mild reaction conditions with low scrambling.

Full kinetics investigation of the formation reaction of phosphonate esters in the gas-phase: a theoretical study

In the present work, the proposed multiple-mechanisms have been investigated theoretically for the reaction between triphenyl phosphite and dimethyl acetylenedicarboxylate in the presence of N-H acid such as aniline for generation of phosphonate esters using ab initio molecular orbital theory in gas phase. The profile of the potential energy surface was constructed at the HF/6-311G(d,p) level of theory. The kinetics of the gas phase reaction was studied by evaluating the reaction path of various mechanisms. Between 12 speculative proposed mechanisms {step₁, step₂ (with four possibilities), step₃ (with three possibilities), and step₄} only the third speculative mechanism was recognized as a desirable mechanism. Theoretical kinetics data involving k and E(a), activation (ΔG(‡), ΔS(‡) and ΔH(‡)), and thermodynamic parameters (ΔG°, ΔS° and ΔH°) were calculated for each step of the various mechanisms. Step₁ of the desirable mechanism was identified as the rate determining step. Comparison of the theoretical desirable mechanism with the rate law that has been previously obtained by UV spectrophotometry experiments indicated that the results are in good agreement.

Mechanistic Study of the Formation of a Phosphonate Ester Containing 2-Fluoroaniline: Theoretical Assignment of the Resulting Isomer

For the first time, theoretical calculations have been employed for assignment of the most stable isomers ([(2S*, 3S*) or (2R*, 3R*)] and [(2S*, 3R*) or (2R*, 3S*)] of a phosphonate ester containing 2-fluoroaniline at HF/6-31G(d,p) and B3LYP/6-311++G(d,p) levels of theory. The results were showed that the compound with gauche arrangement and [(2S*, 3S*) or (2R*, 3R*)] configuration was more stable than the anti arrangement with [(2S*, 3R*) or (2R*, 3S*)] geometry. In addition, experimental 1H, 13C and 31P NMR data along with X-ray crystallographic data of the compound were consistent with the results obtained from theoretical calculations. Kinetic studies were performed on the reaction between triphenyl phosphite, dialkylacetylene dicarboxylates in the presence of an NH-acid, namely as 2-fluoroaniline (as a protic/nucleophilic reagent) for the generation of the compound with a gauche arrangement and [(2S*, 3S*) or (2R*, 3R*)] configuration. Kinetic data were obtained spectrophotometrically and a temperature study yielded activation parameters. A mechanistic scheme is proposed which fits all the kinetic data.

Theoretical Study, An Efficient Synthesis Route to, and Kinetic Investigation of, Stable Phosphorus Ylides Derived from Benzamide

The synthesis, theoretical study and a kinetics and mechanistic investigation are described as a one-pot condensation reaction between benzamide and acetylenic esters in the presence of triphenyphosphine to generate a novel stable phosphorus ylides. For the first time, theoretical calculations have been employed to assign the most stable isomers ( Z or E) of phosphorus ylides 4a-c by AIM and NBO theory, in which Z-4(a,b) are the more stable forms, whereas Z-4c appears as a single isomer. In these cases, the 1H, 13C and 31P NMR spectra of these ylides are consistent with the results obtained from theoretical calculations. Kinetic investigation of the new ylides was undertaken by UV. Useful information was obtained from studies of the effect of solvent, structure of reactants (different alkyl groups within the acetylenic esters), and also the concentration of reactants on the rate of reactions. The proposed mechanism was consistent with the results obtained; from the steady-state approximation, the first step ( k2) of the reaction was recognized as the rate-determining step on the basis of the experimental data.

Stable phosphorus ylides and heterocyclic phosphonate esters derivatives synthesised from stereoselective reactions between triphenyl phosphite and activated acetylenic esters

One-pot synthesis of stable heterocyclic phosphorus ylides 4a–j is reported in fairly good yields by the reaction between dialkyl acetylenedicarboxylates and triphenyl phosphite in the presence of strong NH-acids such as 2-benzoxazolinone, 2-indolinone and 2-mercaptobenzoxazole in aqueous media as an environmentally friendly solvent. The hydrolysis of compounds 4a–f led to stable phosphonate ester derivatives 5h–l. The configuration of compounds 5h–l (2S*,3R*) was determined on the basis of coupling constant predicted from the Karplus equation.

Three-component synthesis of functionalized 5-oxo-4,5-dihydroindeno[1,2-b]pyrans

Protonation of the reactive intermediates produced in the reaction between alkyl(aryl) isocyanides and dialkyl acetylenedicarboxylates by indan-1,3-dione leads to vinylnitrilium cations, which undergo carbon centered Michael type addition with the conjugate base of the CH-acid to produce functionalized 5-oxo-4,5-dihydroindeno[1,2-b]pyrans.

Three-component reaction between triphenylphosphine, dialkyl acetylenedicarboxylates and urea or N-methylurea

The stabilized phosphoranes, obtained from the three-component reaction between dialkyl acetylenedicarboxylates and urea or N-methylurea in the presence of triphenylphosphine, undergo a smooth reaction in boiling toluene to produce iminophosphoranes in good yields. Under the same reaction conditions, the phosphorane obtained from N-methylurea and dimethyl acetylenedicarboxylate yields methyl 1-methyl-2,6-dioxo-1,2,3,6-tetrahydro-pyrimidine-4-carboxylate.