Direct synthesis of aliphatic vinyl aziridines

The synthesis of vinyl aziridines, by the reactions of a range of diphenylphosphinyl and p-toluenesulfonyl alkyl aldimines with the ylide derived from S-allyl tetrahydrothiophenium bromide, are reported.     

Regio- and stereoselective synthesis of highly functionalized vinyl ethers via coiodination of acetylenic ketones

A Cu(OTf)₂-catalyzed highly regio- and stereoselective coiodination of acetylenic ketones was reported, providing a mild and convenient method for the synthesis of (Z)-β-carbonyl-β-iodoenol ethers in good yields.     

New one-pot procedure for the synthesis of diprotected amino alcohols from unprotected vinyl aziridines

An unprecedented one-pot reaction that allows the synthesis of diprotected amino alcohols from unprotected vinyl aziridines is reported. The results demonstrate the possibility to use various acyl chlorides in order to obtain differently functionalised fragments. Mechanistic insights are given.     

Nickel-catalyzed reactions of vinyl aziridines and aziridinylen-ynes

Ni/NHC was found to catalyze the rearrangement of vinyl aziridines and aziridinylen-ynes under mild conditions.     

Cinchona alkaloids in the asymmetric synthesis of 2-(phenylsulfanyl)aziridines

Enantioselective aza-Michael initiated ring closure (MIRC) additions of ethyl nosyloxycarbamate to 2-(phenylsulfanyl)-2-cycloalkenones catalysed by Cinchona alkaloids were studied. The results suggest that the enantioselectivity obtained is influenced by the structure of the catalyst and the different amination conditions. Substrate ring size also plays an important role.     

Mechanistic approaches to asymmetric synthesis of aziridines from guanidinium ylides and aryl aldehydes

To approach more realistic mechanisms for asymmetric aziridine synthesis from guanidinium ylides and aryl aldehydes, reactions were systematically carried out by using a variety of p-substituted benzaldehydes under modified conditions. Two kinds of reaction mechanisms controlled by the nature of the p-substituents of aryl aldehydes is proposed for the two-steps aziridine synthesis composed of a C-C bond formation by nucleophilic addition of guanidinium ylides to aryl aldehydes (step 1) and the fragmentation of intermediate adducts to aziridine products by intramolecular nucleophilic substitution (step 2). A S_Ni-like mechanism via cationic-like transition state is proposed for step 2 in the asymmetric synthesis using EDG-substituted benzaldehydes, whereas with EWG-substituted benzaldehydes, a S_N2-like mechanism is proposed. Hammett analysis, based on the diastereomeric ratio in the aziridine products, is consistent with the proposed rate-determining steps in these two mechanisms. A second Hammett analysis, based on the enantiomeric ratio of the aziridine products, clearly reveals the difference in the susceptibilities to the electronic substituents effect between step 1 and step 2.     

Fragmentation of carbohydrate anomeric alkoxyl radicals. Synthesis of highly functionalized chiral vinyl sulfones

The reaction of derivatives of 3-acetyl-d-glucal, 3-acetyl-l-rhamnal, 3-acetyl-d-galactal, and 3-acetyl-d-lactal with sodium benzenesulfinate in acid medium catalyzed by HgSO₄ afforded diastereoisomeric mixtures of the corresponding 2,3-dideoxy-3-(phenylsulfonyl)-hexopyranoses through a Ferrier rearrangement. The anomeric alkoxyl radical fragmentation of these γ-hydroxy sulfones using the system (diacetoxyiodo)benzene and iodine gave vinyl sulfones with structures of 1,2-dideoxy-4-O-formyl-2-(phenylsulfonyl)-pent-1-enitol and configurations d-erythro, l-erythro, and d-threo at the two stereogenic centers.     

Coupling of vinyl aziridines and phenyl isocyanate

Thermal coupling of vinyl aziridines and phenyl isocyanate was evaluated. Although oxazolidinone products were predominant, some reactions afforded a seven-membered ring heterocycle. When Ni/IMes was employed as a catalyst, a wider array of vinyl aziridines underwent coupling reactions. The Ni catalyzed reactions generally afforded vinyl imidazolidinones as major products.     

Stereoselective Heck arylation of a functionalized cyclopentenyl ether using (S)-N-methyl-pyrrolidine as the stereochemical controller

The study of a series of palladium(0)-catalyzed C2-arylations of a 1-cyclopentenyl ether equipped with a chiral (S)-N-methyl-pyrrolidine auxiliary is reported. Stereoselective Heck monoarylations were performed using aryl iodides under classical heating conditions for 1.7-3.0 h at 80 °C and in one case using 30 min of microwave irradiation at 110 °C. To further explore the scope and nature of this stereoselective methodology, aryl bromides were also utilized as arylating agents, using 20 min of microwave processing at 120-130 °C. High to excellent diastereopurities (90-98% de) were obtained according to ¹H NMR and GC-MS analyses. The prolinol fragment apparently controlled the diastereoselectivity of the Heck reaction by presenting the arylpalladium species from the preferred side of the double bond. By X-ray structure diffraction analysis of an N-quaternized Heck product, the absolute configuration of the new stereocenter was established as (R), supporting a Si-face migratory insertion.     

A convenient and efficient ring-opening reaction of aziridines with acetylenes and synthesis of dihydropyrroles

In the presence of ^tBuOK, reaction of acetylenes with N-Ts substituted aziridines derived from both cyclic and acyclic alkenes at room temperature gave rise to homopropargylamines in good to high yields and in high regioselectivity. Not only Ph- and Me₃Si-substituted acetylenes but also acetylene itself was suitable reagents. Treatment of ring-opening products with I₂ and AgOAc in the presence of K₂CO₃ provided dihydropyrroles in high yields. One-pot synthesis of dihydropyrroles was also realized by the reaction of aziridines and phenylacetylene in the presence of NaH followed by the treatment with I₂ and AgOAc.     

Reaction of primary amines with Pt/C catalyst in water under microwave irradiation: a convenient synthesis of secondary amines from primary amines

Upon microwave irradiation in water, Pt/C converts primary amines into secondary amines in good yield via retro-reductive and reductive amination.     

Regioselective synthesis of highly-substituted biaryls by reaction of vinyl malononitriles with acetylenic esters

The one-pot procedure for synthesis of highly-substituted biaryl derivatives has been described via cyclocondensation reaction between vinyl malononitriles and acetylenic esters. A series of complex biaryls containing one-donor and three-acceptor moieties was obtained with good yields.     

Direct alkylation of thiophenes via bis-coupling with vinyl acetates

A novel direct alkylation of thiophenes via bis-coupling with vinyl acetates has been developed. To the best of our knowledge, this represents the first report of the iron-catalysed coupling of two thiophenes with vinyl groups. Utilizing earth-abundant, inexpensive, and non-toxic iron catalysts, this methodology converts simple thiophenes to symmetrical dithienylethane derivatives under mild conditions in one step.     

FeCl3: an efficient catalyst for reactions of electron-rich arenes with imines or aziridines

Iron(III) chloride was discovered highly effective as catalyst in the Friedel-Crafts reactions of electron-rich arenes with imines or aziridines. It was found that reactions of imines were highly substrate-dependent, which generated mono- or double-addition products, while arenes reacted with aziridines regioselectively leading to the formation of desired ring-opening products in 2 min with moderate to good yields.     

Zirconyl chloride: an efficient recyclable catalyst for synthesis of 5-aryl-2-oxazolidinones from aziridines and CO2 under solvent-free conditions

Zirconyl chloride was found to be an efficient catalyst for the cycloaddition reaction of aziridines with CO₂, thus leading to the preferential formation of 5-aryl-2-oxazolidinones under solvent-free conditions. The methodology could be extended to various substituted aziridines with high conversion and chemo-, regio-, and stereoselectivity. Furthermore, the catalyst could be reused over five times without significant loss in activity. Interestingly, the recovered catalyst showed higher activity in comparison with the fresh catalyst, presumably due to its morphological variation. The use of this cheap and moisture stable catalyst make this protocol practical, environmentally benign, and economically attractive.     

MnIII-catalyzed phosphorylation of vinyl azides: The synthesis of β-keto phosphine oxides

Mn^III-catalyzed functionalization of vinyl azides via phosphorylation was developed to synthesize various β-keto phosphine oxides in high yields. The transformation is operated in mild conditions and tolerant of a range of functional groups. Control reaction indicates that the reaction mechanism might proceed via the generation of a phosphonated iminyl radical intermediate.     

Synthesis of vinyl sulfides via hydrothiolation of alkynes using Al2O3/KF under solvent-free conditions

We present here a clean, solvent-free hydrothiolation of alkynes using solid supported catalyst (Al₂O₃/KF). This efficient and improved method selectively furnishes the corresponding anti-Markovnikov vinyl sulfides in good to excellent yields. The method is applicable for aliphatic and aromatic thiols and the catalytic system can be re-used up to two times without previous treatment and with comparable activity.     

Diastereoselective synthesis of functionalized tetrahydro-γ-carbolines via a [3 + 3] cycloaddition of 2,2′-diester aziridines with β-(indol-2-yl)-α,β-unsaturated ketones

A Sc(OTf)₃-catalyzed [3 + 3] cycloaddition of 2,2′-diester aziridines with β-(indol-2-yl)-α,β-unsaturated ketones was developed, affording polysubstituted tetrahydro-γ-carbolines in single diastereoisomers in good to excellent yields.     

Synthesis of 1,2,5- and 1,2,3,5-substituted pyrroles from substituted aziridines via Ag(I)-catalyzed intramolecular cyclization

An efficient synthesis of 1,2,5- and 1,2,3,5-substituted pyrroles has been achieved from the sequential reactions including a ring-opening of 1-(aziridin-2-yl)propargylic alcohols by various nucleophiles under mild condition followed by an intramolecular cyclization using Ag(I) catalyst.     

Synthesis of trans-perhydroisoquinolines by 6-endo-trig radical cyclization of amino-tethered vinyl bromides and cyclohexenes

Bu₃SnH-promoted cyclization of several N-(2-bromoprop-2-enyl)-N-[(4-oxocyclohex-1-enyl)methyl]alkylamines is reported. It has been found that the generated vinyl radicals evolve through a 6-endo-cyclization pathway giving rise to the corresponding 4,6-functionalized perhydroisoquinolines in a prevalent trans-relative configuration.