In organic chemistry, aziridines are organic compounds containing the aziridine functional group (chemical structure (R−)4C2N−R), a three-membered heterocycle with one amine (>NR) and two methylene bridges (>CR2). [2] [3] [4] The parent compound is aziridine (or ethylene imine), with molecular formula C2H4NH. Several drugs feature aziridine rings, including mitomycin C, porfiromycin, and azinomycin B (carzinophilin). [5]
The bond angles in aziridine are approximately 60°, considerably less than the normal hydrocarbon bond angle of 109.5°, which results in angle strain as in the comparable cyclopropane and ethylene oxide molecules. A banana bond model explains bonding in such compounds. Aziridine is less basic than acyclic aliphatic amines, with a pKa of 7.9 for the conjugate acid, due to increased s character of the nitrogen free electron pair. Angle strain in aziridine also increases the barrier to nitrogen inversion. This barrier height permits the isolation of separate invertomers, for example the cis and trans invertomers of N-chloro-2-methylaziridine.
Several routes have been developed for the syntheses of aziridines (aziridination).
An amine functional group displaces the adjacent halide in an intramolecular nucleophilic substitution reaction to generate an aziridine. The parent aziridine is produced industrially from aminoethanol via two related routes. The Nippon Shokubai process requires an oxide catalyst and high temperatures to effect the dehydration. In the Wenker synthesis, the aminoethanol is converted to the sulfate ester, which undergoes base-induced sulfate elimination. [6]
Nitrene addition to alkenes is a well-established method for the synthesis of aziridines. Photolysis or thermolysis of organic azides are good ways to generate nitrenes. Nitrenes can also be prepared in situ from iodosobenzene diacetate and sulfonamides, or the ethoxycarbonylnitrene from the N-sulfonyloxy precursor. [7]
Thermolysis or photolysis of triazolines expels nitrogen, producing an aziridine.
In the Blum-Ittah aziridine synthesis, sodium azide opens an epoxide, followed by reduction of the azide with triphenylphosphine accompanied by expulsion of nitrogen gas: [8]
Another method involves the ring-opening reaction of an epoxide with amines, followed by ring closing with the Mitsunobu reaction. [9]
The Hoch-Campbell ethylenimine synthesis involves the reaction of certain oximes with Grignard reagents, which affords aziridines. [10]
Aziridines are obtained by treating a mono-, di-, tri- or tetra-substituted alkene (olefin) with O-(2,4-dinitrophenyl)hydroxylamine (DPH) in the presence of rhodium catalysts:
For instance, 2-phenyl-3-methylaziridine can be synthesized by this method and then converted by ring opening reaction to (D)- and (L)-amphetamine (the two active ingredients in Adderall). [11]
The De Kimpe aziridine synthesis allows for the generation of aziridines by reacting an α-chloroimine with a nucleophile, such as hydride, cyanide, or a Grignard reagent. [12] [13]
2-azido alcohols can be converted into aziridines with the use of trialkyl phosphines such as trimethylphosphine or tributylphosphine. [14] [15]
Aziridines are reactive substrates in ring-opening reactions with many nucleophiles due to their ring strain. Alcoholysis and aminolysis are basically the reverse reactions of the cyclizations. Carbon nucleophiles such as organolithium reagents and organocuprates are also effective. [16] [17]
One application of a ring-opening reaction in asymmetric synthesis is that of trimethylsilylazide TMSN
3 with an asymmetric ligand [18] in scheme 2 [19] in an organic synthesis of oseltamivir:
Certain N-substituted azirines with electron withdrawing groups on both carbons form azomethine ylides in an electrocyclic thermal or photochemical ring-opening reaction. [20] [21] These ylides can be trapped with a suitable dipolarophile in a 1,3-dipolar cycloaddition. [22]
When the N-substituent is an electron-withdrawing group such as a tosyl group, the carbon-nitrogen bond breaks, forming another zwitterion TsN−
–CH
2–CH+
2–R [23]
This reaction type requires a Lewis acid catalyst such as boron trifluoride. In this way 2-phenyl-N-tosylaziridine reacts with alkynes, nitriles, ketones and alkenes. Certain 1,4-dipoles form from azetidines.
Lewis acids, such as B(C
6F
5)
3, can induce decomposition of the ring to a carbocation and linear azanide, which then attack unsaturated moieties in tandem. [24] Oxidation to the N-oxide instead induces nitroso compound extrusion, leaving an olefin. [25]
As electrophiles, aziridines are subject to attack and ring-opening by endogenous nucleophiles such as nitrogenous bases in DNA base pairs, resulting in potential mutagenicity. [26] [27] [28]
The International Agency for Research on Cancer (IARC) classifies aziridine compounds as possibly carcinogenic to humans (IARC Group 2B). [29] In making the overall evaluation, the IARC Working Group took into consideration that aziridine is a direct-acting alkylating agent, which is mutagenic in a wide range of test systems and forms DNA adducts that are promutagenic. The features that are responsible for their mutagenicity are relevant to their beneficial medicinal properties. [5]
Elias James Corey is an American organic chemist. In 1990, he won the Nobel Prize in Chemistry "for his development of the theory and methodology of organic synthesis", specifically retrosynthetic analysis.
In organic chemistry, an epoxide is a cyclic ether, where the ether forms a three-atom ring: two atoms of carbon and one atom of oxygen. This triangular structure has substantial ring strain, making epoxides highly reactive, more so than other ethers. They are produced on a large scale for many applications. In general, low molecular weight epoxides are colourless and nonpolar, and often volatile.
An enamine is an unsaturated compound derived by the condensation of an aldehyde or ketone with a secondary amine. Enamines are versatile intermediates.
A protecting group or protective group is introduced into a molecule by chemical modification of a functional group to obtain chemoselectivity in a subsequent chemical reaction. It plays an important role in multistep organic synthesis.
In chemistry, a nitrene or imene is the nitrogen analogue of a carbene. The nitrogen atom is uncharged and monovalent, so it has only 6 electrons in its valence level—two covalent bonded and four non-bonded electrons. It is therefore considered an electrophile due to the unsatisfied octet. A nitrene is a reactive intermediate and is involved in many chemical reactions. The simplest nitrene, HN, is called imidogen, and that term is sometimes used as a synonym for the nitrene class.
The Pauson–Khand (PK) reaction is a chemical reaction, described as a [2+2+1] cycloaddition. In it, an alkyne, an alkene, and carbon monoxide combine into a α,β-cyclopentenone in the presence of a metal-carbonyl catalyst Ihsan Ullah Khand (1935–1980) discovered the reaction around 1970, while working as a postdoctoral associate with Peter Ludwig Pauson (1925–2013) at the University of Strathclyde in Glasgow. Pauson and Khand's initial findings were intermolecular in nature, but the reaction has poor selectivity. Some modern applications instead apply the reaction for intramolecular ends.
The Curtius rearrangement, first defined by Theodor Curtius in 1885, is the thermal decomposition of an acyl azide to an isocyanate with loss of nitrogen gas. The isocyanate then undergoes attack by a variety of nucleophiles such as water, alcohols and amines, to yield a primary amine, carbamate or urea derivative respectively. Several reviews have been published.
Azomethine ylides are nitrogen-based 1,3-dipoles, consisting of an iminium ion next to a carbanion. They are used in 1,3-dipolar cycloaddition reactions to form five-membered heterocycles, including pyrrolidines and pyrrolines. These reactions are highly stereo- and regioselective, and have the potential to form four new contiguous stereocenters. Azomethine ylides thus have high utility in total synthesis, and formation of chiral ligands and pharmaceuticals. Azomethine ylides can be generated from many sources, including aziridines, imines, and iminiums. They are often generated in situ, and immediately reacted with dipolarophiles.
The Barton–Kellogg reaction is a coupling reaction between a diazo compound and a thioketone, giving an alkene by way of an episulfide intermediate. The Barton–Kellogg reaction is also known as Barton–Kellogg olefination and Barton olefin synthesis.
In organic chemistry, episulfides are a class of organic compounds that contain a saturated, heterocyclic ring consisting of two carbon atoms and one sulfur atom. It is the sulfur analogue of an epoxide or aziridine. They are also known as thiiranes, olefin sulfides, thioalkylene oxides, and thiacyclopropanes. Episulfides are less common and generally less stable than epoxides. The most common derivative is ethylene sulfide.
The Fürst-Plattner rule describes the stereoselective addition of nucleophiles to cyclohexene derivatives.
Electrophilic amination is a chemical process involving the formation of a carbon–nitrogen bond through the reaction of a nucleophilic carbanion with an electrophilic source of nitrogen.
An oxaziridine is an organic molecule that features a three-membered heterocycle containing oxygen, nitrogen, and carbon. In their largest application, oxaziridines are intermediates in the industrial production of hydrazine. Oxaziridine derivatives are also used as specialized reagents in organic chemistry for a variety of oxidations, including alpha hydroxylation of enolates, epoxidation and aziridination of olefins, and other heteroatom transfer reactions. Oxaziridines also serve as precursors to nitrones and participate in [3+2] cycloadditions with various heterocumulenes to form substituted five-membered heterocycles. Chiral oxaziridine derivatives effect asymmetric oxygen transfer to prochiral enolates as well as other substrates. Some oxaziridines also have the property of a high barrier to inversion of the nitrogen, allowing for the possibility of chirality at the nitrogen center.
The Tsuji–Trost reaction is a palladium-catalysed substitution reaction involving a substrate that contains a leaving group in an allylic position. The palladium catalyst first coordinates with the allyl group and then undergoes oxidative addition, forming the π-allyl complex. This allyl complex can then be attacked by a nucleophile, resulting in the substituted product.
Rearrangements, especially those that can participate in cascade reactions, such as the aza-Cope rearrangements, are of high practical as well as conceptual importance in organic chemistry, due to their ability to quickly build structural complexity out of simple starting materials. The aza-Cope rearrangements are examples of heteroatom versions of the Cope rearrangement, which is a [3,3]-sigmatropic rearrangement that shifts single and double bonds between two allylic components. In accordance with the Woodward-Hoffman rules, thermal aza-Cope rearrangements proceed suprafacially. Aza-Cope rearrangements are generally classified by the position of the nitrogen in the molecule :
Hydroxylamine-O-sulfonic acid (HOSA) or aminosulfuric acid is the inorganic compound with molecular formula H3NO4S that is formed by the sulfonation of hydroxylamine with oleum. It is a white, water-soluble and hygroscopic, solid, commonly represented by the condensed structural formula H2NOSO3H, though it actually exists as a zwitterion and thus is more accurately represented as +H3NOSO3−. It is used as a reagent for the introduction of amine groups (–NH2), for the conversion of aldehydes into nitriles and alicyclic ketones into lactams (cyclic amides), and for the synthesis of variety of nitrogen-containing heterocycles.
In organic chemistry, the Davis oxidation or Davis' oxaziridine oxidation refers to oxidations involving the use of the Davis reagent or other similar oxaziridine reagents. This reaction mainly refers to the generation of α-hydroxy carbonyl compounds (acyloins) from ketones or esters. The reaction is carried out in a basic environment to generate the corresponding enolate from the ketone or ester. This reaction has been shown to work for amides.
The De Kimpe aziridine synthesis is a name reaction of organic chemistry, for the generation of aziridines by the reaction of α-chloroimines with nucleophiles such as hydride, cyanide, or Grignard reagents.
The Blum–Ittah aziridine synthesis, also known as the Blum–Ittah-Shahak aziridine synthesis or simply the Blum aziridine synthesis is a name reaction of organic chemistry, for the generation of aziridines from oxiranes.
An organic azide is an organic compound that contains an azide functional group. Because of the hazards associated with their use, few azides are used commercially although they exhibit interesting reactivity for researchers. Low molecular weight azides are considered especially hazardous and are avoided. In the research laboratory, azides are precursors to amines. They are also popular for their participation in the "click reaction" between an azide and an alkyne and in Staudinger ligation. These two reactions are generally quite reliable, lending themselves to combinatorial chemistry.
