Selectivity aspects of the ring opening reaction of 2-alkenyl aziridines by carbon nucleophiles

A series of common organometallic reagents were used in the reaction with an acyclic and a cyclic activated 2-alkenyl aziridines and the selectivity aspects for each aziridine was addressed.     

[2 + 2]-Cycloreversions

Four-membered rings can be cleaved thermally, Photochemically, or catalytically into two π bonded fragments. Theoretical calculations, kinetic studies, and investigations of stereo- and regioselectivity have been undertaken to clarify the question of whether the reaction involves one or two steps and to permit predictions on its course. [2 + 2]-Cycloreversions have been used to clarify the structure of four-membered rings, to prepare highly reactive π electron-systems and–in combination with a [2 + 2]-cycloaddition–to protect double bonds. The combination of a cycloaddition and-reversion can be used to convert a carbonyl group into an olefin. Starting with compounds containing annelated four-membered rings, compounds with two functional groups or large ring systems can be prepared. [2 + 2]-Cycloreversions have also been discussed in connection with storage of solar energy.     

Efficient synthesis of functionalized furans and benzofurans based on a ‘[3+2] cyclization/oxidation’ strategy

Functionalized furans and benzofurans were prepared by DDQ oxidation of 2-alkylidenetetrahydrofurans, which are readily available by one-pot cyclizations of 1,3-dicarbonyl dianions or 1,3-bis-silyl enol ethers.     

Preparation of 2,3-diaminopropionate from ring opening of aziridine-2-carboxylate

Ring opening reaction of an enantiomerically pure aziridine-2-carboxylate with an azide nucleophile under aqueous acidic media proceeded efficiently and stereoselectively to give 3-amino-2-azidopropionate which is converted to orthogonally protected 2,3-diaminopropionate.     

Ring opening reactions of 1-arenesulfonyl-2-(bromomethyl)aziridines

The reactivity of 1-arenesulfonyl-2-(bromomethyl)aziridines with respect to lithium dialkylcyanocuprates and lithium dialkylcuprates (Gilman reagents) has been evaluated for the first time, pointing to the conclusion that these substrates can be applied successfully as synthetic equivalents for the 2-aminopropane dication synthon towards 2-alkylaziridines and α-branched N-tosylamides in good yields.     

Ring opening of 2-(bromomethyl)-1-sulfonylaziridines towards 1,3-heteroatom substituted 2-aminopropane derivatives

1,3-Heteroatom substituted 2-aminopropane derivatives have been prepared from 2-(bromomethyl)-1-sulfonylaziridines for the first time using sodium azide or different potassium phenoxides in water in the presence of silica gel. The applicability of 1-arenesulfonyl-2-(bromomethyl)aziridines for the synthesis of functionalized sulfonamides has also been demonstrated towards different 1,3-dialkoxy-2-(tosylamino)propanes and 1,3-dialkylthio-2-(tosylamino)propanes upon treatment with the appropriate sodium alkoxide or sodium alkylthiolate in the corresponding alcohol or in methanol, respectively.     

Ring opening of 2-acylaziridines by acid chlorides

Good nucleophilicity of the ring nitrogen in chiral (2R,1′R)-2-acyl-(1′-phenylethyl)aziridines initiated the reaction with various acid chlorides to form the corresponding acylaziridinium ion intermediates whose rings were opened by the chloride anion to yield the β-amino-α-chlorocarbonyl compounds. The subsequent displacement of the chloride with the internal oxygen nucleophile originated from methylchloroformate, acetyl chloride, and methyl chlorooxoacetate yielded oxazolidin-2-ones, β-amino-α-acetyloxypropionates, and morpholin-2,3-diones, respectively.     

Recent Developments in the Stereochemistry of Cyclopropane Ring Opening

This review article deals with the stereochemistry of the following ring opening reactions: 1. Homoallylic rearrangement of secondary and tertiary cyclopropyl alcohols in the presence of electrophilic reagents, 2. The addition of carboxylic acids to vinylcyclopropanes, 3. The thermal rearrangement of vinylcyclopropanes into cyclopentenes. An account is also given of the NMR spectroscopic determination of the conformations of substituted vinylcyclopropanes.     

2,2’─呋喃联吡咯型联体杂环化合物的合成

在强极性的醇酸体系中，利用Knorr－Paal反应制得了呋喃联吡咯系的13个新化合物，并进行了红外光谱、质谱、核磁共振谱及元素分析测定。     

Novel synthesis of 2-aminopentanedinitriles from 2-(bromomethyl)aziridines and their transformation into 2-imino-5-methoxypyrrolidines and 5-methoxypyrrolidin-2-ones

1-Arylmethyl-2-(bromomethyl)aziridines were transformed into 2-[N-(arylmethyl)amino]pentanedinitriles upon treatment with an excess of potassium cyanide in DMSO through an unprecedented and peculiar reaction mechanism, involving base-induced ring opening of intermediate 2-(cyanomethyl)aziridines into allylamines, followed by migration of the double bond out of the conjugation towards aldimines via enamine intermediates. The resulting aminopentanedinitriles served as substrates for the synthesis of novel 2-imino-5-methoxypyrrolidines upon treatment with sodium methoxide in methanol, which were either acetylated at the free imino group to afford the more stable N-acetylimino derivatives or hydrolyzed towards the corresponding synthetically relevant 5-methoxypyrrolidin-2-ones.     

About diastereoselective oxidations of ferrocenyl amino alcohols

Oxidation of some 2-(N,N-dimethylaminomethyl)ferrocenylalkylcarbinols by MnO₂ is totally diastereoselective: only one diastereomer is oxidized. A study was performed to highlight the influential factors of this phenomenon. Several ferrocenyl alcohols have been studied. First, two diastereomers of the ferrocenyl amino alcohol bearing a deuterium as an R group have been synthesized and oxidized. The good reactivity of both diastereomers displayed the importance of the size of the alkyl group, which needs to be bulkier than a deuterium. The synthesis and the oxidation of endo- and exo-α-hydroxy [4](1,2)ferrocenophane enabled the elimination of the hypothesis involving the spatial position of the hydroxy group, while the two diastereomers were oxidized. The replacement of the dimethylamino group by a methoxy or a methyl, the oxidation of these compounds, and the study of the preferential conformation of each diastereomer showed clearly the influence of an intramolecular hydrogen bond. So,the diastereoselectivity was shown to depend on the steric bulk of the alkyl group and on the presence of a strong intramolecular hydrogen bond between the hydroxy group and the nitrogen.     

Reinvestigation of the conversion of epoxides into halohydrins with elemental halogen catalysed by thiourea

In contrast to a previous literature report, thiourea is not a catalyst in the ring opening reaction of epoxides by means of bromine or iodine. Instead, thiourea reacts with the halogen to give a complex mixture of products, among them hydrogen halogenides, which are in fact the real epoxide ring opening reactants. The presence of water is crucial in this reaction.     

SYTHESIS AND ANIONIC POLYMERIZATION OF 2-METHYL-2-METHOXYCARBONYL-5-METHYLENE-1, 3-DIOXOLAN-4-ONE

A new cyclic monomer, 2-methyl-2-methoxycarbonyl-5-methylene-1,3-dioxolan-4-one,was synthesized successfully. The monomer and intermediate were characterized by ~1H NMR, ~(13)CNMR, INEPT(Intensive Nuclei Enhanced by Polarization Transfer) technique, IR and elementalanalysis. Anionic polymerization of the monomer was carried out in anhydrous THF at -70℃,and 9-fluorenyllithium was used as initiator. The polymer structure was determined by IR, NMRand elemental analysis. Molecular weight of the polymer was estimated by viscosity measurementin DMSO at 30℃.     

Regioselective ring opening of 2-methylaziridine derivatives with F- and F-fluoride

Regioselectivity of the nucleophilic ring opening of N-benzoyl (Bz) and N-benzyloxycarbonyl (Cbz) activated 2-methylaziridines with anhydrous tetramethylammonium fluoride, anhydrous hydrogen fluoride, and ¹⁹F or [¹⁸F]-labelled potassium cryptand fluoride ([K₂₂₂][^18/19F]) were investigated. Whereas all reactions with rigorously anhydrous N(CH₃)₄F did not ring-open the aziridines, reactions with anhydrous HF exclusively yielded the 2-fluoropropanamine derivatives. Reactions of Bz-protected and Cbz-protected 2-methylaziridine with [K₂₂₂][^18/19F] yielded the 2-fluoropropanamine and 1-fluoro-2-propanamine derivatives as the major products, respectively, and represents the first example of regiocontrol during ring opening of aziridines with [¹⁸F]-fluoride.     

Transformations of 3-aryl-2-chloro-2-imidoylaziridines: novel entries to 4-chloro-2,5-diaryl-1H-imidazoles and 2-chloro-2-acylaziridines

The reactivity of stereochemically defined 3-aryl-2-chloro-2-imidoylaziridines, an unexplored class of substituted aziridines, was investigated under various reaction conditions. 2-Chloro-2-imidoylaziridines underwent a novel thermal rearrangement by reflux in acetonitrile via C-C bond cleavage to 4-chloro-2,5-diarylimidazoles in high yield. Alternatively, a novel efficient entry toward 2-aroyl-2-chloroaziridines was based on the chemoselective hydrolysis of 2-chloro-2-imidoylaziridines with hydrochloric acid in aqueous tetrahydrofuran.     

SYNTHESIS AND ANIONIC POLYMERIZATION OF 2-METHYL-2-METHOXY CARBONYL-5-METHYLENE-1, 3-DIOXOLAN-4-ONE

A new cyclic monomer, 2-methyl-2-methocycarbonyl-5-methylene 1,3-dioxlan-4-one,wassynthesized successfully. The monomer and intermediate were characterized by ~1H NMR,~(13)C NMR, INEPT (Intensive Nuclei Enhanced by Polarization Transfer) technique, IR andelemental analysis. Anionic polymerization of the monomer was carried out in anhydrous THF at.70℃, and 9-fluorenyllithium was used as initiator. The polymer strucure was determined byIR, NMR and elemental analysis. Molecular weight of the polymer was estimated by viscositymeasurement in DMSO at 30℃.     

5-Hydroxy-2H-pyrrol-2-ones and not 2-aminofurans are the cycloaddition products between alkyl isocyanides and benzyliden-1,3-diketones

New insights into the cycloaddition reaction between alkyl isocyanides and benzyliden-1,3-diketones are reported. 5-Hydroxy-N-substituted-2H-pyrrol-2-ones and not substituted furans, as previously reported, are formed. The proof of the structure relies on a thorough analytical investigation and X-ray crystallography.     

An efficient synthesis of chiral terminal 1,2-diamines using an enantiomerically pure [1-(1′R)-methylbenzyl]aziridine-2-yl]methanol

Enantiomerically pure terminal 1,2-diamines, which can serve as precursors for the synthesis of many biologically important compounds, were synthesized efficiently from a commercially available chiral [1-(1′R)-methylbenzyl]aziridine-2-yl]methanol. Various enantiomerically pure 2-vinylaziridines were prepared by Wittig reactions from aziridine-2-carboxaldehyde and the corresponding phosphonium salts. The C(2)-N bond of the vinyl substituted aziridine ring was regioselectively cleaved by azidotrimethylsilane (TMSN₃). The azido group and the double bond were reduced successively to give the target compounds in high yields.     

Preparation of enantiopure 2-acylazetidines and their reactions with chloroformates

Enantiopure 1-phenylethylazetidine-2-carboxylates and 2-acylazetidines were prepared and reacted with chloroformates to yield α-chloro-γ-amino butyric acid esters and ketones from ring opening reaction of azetidinium ion intermediate in a completely regio- and stereoselective manner.