Synthetic strategies for the preparation of γ-phostams: 1,2-azaphospholidine 2-oxides and 1,2-azaphospholine 2-oxides

• Jiaxi Xu

Beilstein J. Org. Chem. 2022, 18, 889–915, doi:10.3762/bjoc.18.90

• method to synthesize 1,2-azaphospholidine 2-oxide derivatives 13. Arylphosphinyl azides generate arylphosphinyl nitrenes under photoirradiation. The phosphinyl nitrenes underwent an intramolecular insertion into the ortho C–H bond of the aryl group accompanied with the Curtius-like rearrangement as well

[2 + 1] Cycloaddition reactions of fullerene C₆₀ based on diazo compounds

• Yuliya N. Biglova

Beilstein J. Org. Chem. 2021, 17, 630–670, doi:10.3762/bjoc.17.55

• synthetic organic chemists as it allows to obtain methanofullerenes, fullerenoaziridines, or fullerenooxyranes. These reactions can involve, for example, the addition of stabilized carbanions, carbenes, and nitrenes and can involve various reaction mechanisms. While in the early years of intense research on

Hypervalent organoiodine compounds: from reagents to valuable building blocks in synthesis

• Gwendal Grelier,
• Benjamin Darses and
• Philippe Dauban

Beilstein J. Org. Chem. 2018, 14, 1508–1528, doi:10.3762/bjoc.14.128

• and PhI(OCOt-Bu)2. These λ3-iodanes have been widely used in atom-transfer reactions, particularly for the generation of metal-bound nitrenes that are highly active species for the aziridination of alkenes and the direct amination of benzylic, allylic or tertiary C(sp3)–H bonds [80][81][82][83][84][85

Pd(OAc)₂/Ph₃P-catalyzed dimerization of isoprene and synthesis of monoterpenic heterocycles

• Dominik Kellner,
• Maximilian Weger,
• Andrea Gini and
• Olga García Mancheño

Beilstein J. Org. Chem. 2017, 13, 1807–1815, doi:10.3762/bjoc.13.175

• heterocyclic terpenes by subsequent (hetero)-Diels–Alder or [4 + 1]-cycloadditions with nitrenes is also depicted. Keywords: dimerization; heterocycles; isoprene; monoterpene; palladium catalysis; Introduction The dimerization of conjugated dienes represents a useful, highly atom economic and straightforward

• that are used as alkyd coatings and perfume additives [39][40]. In addition, further functionalization reactions of the isoprene dimers can be carried out. In this work, we envisioned the synthesis of various heterocycles by (hetero)Diels–Alder and [4 + 1]-cycloadditions with nitrenes with the obtained

• maleimides in toluene provided a ready access to the fused ring-system 6a–c in excellent yields (81–91%; Scheme 3, middle). Finally, the [4 + 1]-cycloaddition with nitrenes was carried out (Scheme 3, right). To attain this transformation the required nitrene was formed in situ from an iminoiodinane precursor

The synthesis of functionalized bridged polycycles via C–H bond insertion

• Jiun-Le Shih,
• Po-An Chen and
• Jeremy A. May

Beilstein J. Org. Chem. 2016, 12, 985–999, doi:10.3762/bjoc.12.97

• via C–H bond insertion by carbenes and nitrenes. Applications to natural product synthesis, a description of the essential elements in substrate-controlled reactions, and mechanistic details of transformations are presented. Overall, these transformations allow the construction of important ring

• 1 or 3). This review highlights strategies that leverage C–H bond insertion by carbenes and nitrenes to construct bridged polycycles. This key bond-forming event may construct the bridged ring, or it may construct an additional ring fused to an existing bridged bicycle to synthesize the bridged

• carbenes and nitrenes generated from sulfonate esters prefer 6-membered ring formation (i.e., 1,6-insertion) opened the door for easy access to 1,3-functionalized products via C–H insertion [64][65]. The sulfonate can be a useful functional group for subsequent transformations, also. If used in the

Synthesis of 2,1-benzisoxazole-3(1H)-ones by base-mediated photochemical N–O bond-forming cyclization of 2-azidobenzoic acids

• Daria Yu. Dzhons and
• Andrei V. Budruev

Beilstein J. Org. Chem. 2016, 12, 874–881, doi:10.3762/bjoc.12.86

• -benzisoxazolones; 1,5-electrocyclization; nitrenes; photochemical cyclization; Introduction Substituted 2,1-benzisoxazoles display diverse biological activity [1][2][3][4][5][6] (Figure 1) and are widely used as starting materials for the synthesis of important heterocyclic pharmacophores, such as acridines [7][8

• azepines are formed through the singlet nitrogen pathway of the reaction (Scheme 1, path: 1 → A → B → C → 3) [44][45][46][47][48][49]. These nitrenes form benzazirines [19] (Scheme 1, intermediate B) that rearrange into cyclic ketenimines – 1,2-didehydroazepines (Scheme 1, intermediate C) [50]. According

• through a 1,5-electrocyclization reaction [56][57]. Nonreacted singlet nitrenes A may undergo intersystem crossing (ISC) into the less reactive triplet state (Scheme 1, intermediate D). Although a multiplicity change is a spin-forbidden transition, it can be partially allowed in some cases. According to

The reactions of 2-ethoxymethylidene-3-oxo esters and their analogues with 5-aminotetrazole as a way to novel azaheterocycles

• Marina V. Goryaeva,
• Yanina V. Burgart,
• Marina A. Ezhikova,
• Mikhail I. Kodess and
• Viktor I. Saloutin

Beilstein J. Org. Chem. 2015, 11, 385–391, doi:10.3762/bjoc.11.44

• -carboxylate (5) was isolated as a by-product in the reaction of ester 1a and 5-AT (Scheme 2). Apparently, in this reaction azidopyrimidines 2a,b acted as intermediates that were decomposed under heating in 1,4-dioxane with elimination of nitrogen and nitrenes [26] (Scheme 2). The latter can cleave a hydrogen

[3 + 2]-Cycloadditions of nitrile ylides after photoactivation of vinyl azides under flow conditions

• Stephan Cludius-Brandt,
• Lukas Kupracz and
• Andreas Kirschning

Beilstein J. Org. Chem. 2013, 9, 1745–1750, doi:10.3762/bjoc.9.201

• photoinduced activation of vinyl azides 1, which gives rise to 2H-azirines 2 via vinyl nitrenes after the loss of molecular nitrogen and subsequent ring-opening under photochemical conditions to provide the nitrile ylides 3 (Scheme 1). For recent examples for the use of azirines in organic syntheses please

4-Pyridylnitrene and 2-pyrazinylcarbene

• Curt Wentrup,
• Ales Reisinger and
• David Kvaskoff

Beilstein J. Org. Chem. 2013, 9, 754–760, doi:10.3762/bjoc.9.85

• nitrenes possessing a 1,3-relationship between a nitrene centre and a ring nitrogen atom and leads to nitrile ylides, such as 9 in the case of 3-pyridylnitrene (7), whereby the actual ring opening may take place in either the nitrene itself or the ring-expanded ketenimine 8 (Scheme 2) [6][7][8]. A 1,7-H

• shift finally converts the nitrile ylide 9 to the open-chain ketenimine 10 (Scheme 2). 3-Pyridylcarbene undergoes analogous Type I ylidic ring opening to an ethynylvinylnitrile imine [6]. Type II ring opening is diradicaloid and proceeds via an open-chain vinylnitrene or biradical 13 in nitrenes such as

• -pyridylnitrene (19) and 2-pyrazinylcarbene (21) (Scheme 3). Mild FVT of 18 at 400 °C, even in high vacuum, affords 4,4’-azopyridine (25) in 54% yield [12]. This kind of reaction is typically ascribed to the dimerization of triplet nitrenes. Most importantly, FVT of the pyrazinylcarbene precursor 23 also affords

3-Pyridylnitrene, 2- and 4-pyrimidinylcarbenes, 3-quinolylnitrenes, and 4-quinazolinylcarbenes. Interconversion, ring expansion to diazacycloheptatetraenes, ring opening to nitrile ylides, and ring contraction to cyanopyrroles and cyanoindoles

• Curt Wentrup,
• Nguyen Mong Lan,
• Adelheid Lukosch,
• Pawel Bednarek and
• David Kvaskoff

Beilstein J. Org. Chem. 2013, 9, 743–753, doi:10.3762/bjoc.9.84

• either the nitrenes or the diazacycloheptatetraenes to nitrile ylides. Keywords: carbene-nitrene interconversion; diazepines; flash vacuum thermolysis; matrix photochemistry; nitrile ylides; reactive intermediates; Introduction A multitude of rearrangements of heterocyclic nitrenes have been described

• –60% yield (Scheme 12). Importantly, smaller amounts of amine 51 and the ring-contraction product 2-phenyl-3-cyanoindole (48, 21–15%) were also isolated. Formation of amines is diagnostic for triplet nitrenes, even in low-pressure gas-phase reactions [10][22]. The 3-cyanoindole 48 is expected to be

High-spin intermediates of the photolysis of 2,4,6-triazido-3-chloro-5-fluoropyridine

• Sergei V. Chapyshev,
• Denis V. Korchagin,
• Patrik Neuhaus and
• Wolfram Sander

Beilstein J. Org. Chem. 2013, 9, 733–742, doi:10.3762/bjoc.9.83

• observable nitrenes can be assigned to triplet 2,4-diazido-3-chloro-5-fluoropyridyl-6-nitrene (DT = 1.026 cm−1, ET = 0), triplet 2,6-diazido-3-chloro-5-fluoropyridyl-4-nitrene (DT = 1.122 cm−1, ET = 0.0018 cm−1), quintet 4-azido-3-chloro-5-fluoropyridyl-2,6-dinitrene (DQ = 0.215 cm−1, EQ = 0.0545 cm−1

• spectroscopy; high-spin states; matrix isolation; nitrenes; photolysis; reactive intermediates; Introduction High-spin nitrenes are highly reactive intermediates formed during photolysis or thermolysis of aromatic polyazides. Both these processes are widely used in modern science and technology [1][2][3][4][5

• spectroscopy allowing the reliable identification of isomeric high-spin nitrenes [7][8][9][10]. Thus, previous EPR studies have shown that irradiation of triazide 1a with light at λ = 313 nm selectively gave quintet dinitrene 4a as the major intermediate product (Scheme 1) [7][8]. Most recently, a similar

Towards a biocompatible artificial lung: Covalent functionalization of poly(4-methylpent-1-ene) (TPX) with cRGD pentapeptide

• Lena Möller,
• Christian Hess,
• Jiří Paleček,
• Yi Su,
• Axel Haverich,
• Andreas Kirschning and
• Gerald Dräger

Beilstein J. Org. Chem. 2013, 9, 270–277, doi:10.3762/bjoc.9.33

• , leads to a highly biocompatible poly(methylpentene) surface. The resulting modified membrane preserves the required excellent gas-flow properties while being densely seeded with lung endothelial cells. Keywords: click chemistry; growth factor; nitrenes; plasma chemistry; poly(4-methylpent-1-ene

Metal–ligand multiple bonds as frustrated Lewis pairs for C–H functionalization

• Matthew T. Whited

Beilstein J. Org. Chem. 2012, 8, 1554–1563, doi:10.3762/bjoc.8.177

• cleavage seems to depend on the nature of the metal catalyst. Nevertheless, these results do provide inspiration for the development of similar C–H functionalization catalysis involving metal carbenes or silylenes (or perhaps even electrophilic nitrenes). Utility of M═E FLPs in C–H functionalization Given

C–H Functionalization

• Huw M. L. Davies

Beilstein J. Org. Chem. 2012, 8, 1552–1553, doi:10.3762/bjoc.8.176

• can become broadly applicable. Metal-bound carbenes, nitrenes and oxo species have been particularly effective at stereoselective sp3 C–H functionalization. However, considerable advances still need to be made to enhance the selectivity and to increase the range of functionality that can be introduced

Continuous flow photolysis of aryl azides: Preparation of 3H-azepinones

• Farhan R. Bou-Hamdan,
• François Lévesque,
• Alexander G. O'Brien and
• Peter H. Seeberger

Beilstein J. Org. Chem. 2011, 7, 1124–1129, doi:10.3762/bjoc.7.129

• Berlin, Germany 10.3762/bjoc.7.129 Abstract Photolysis of aryl azides to give nitrenes, and their subsequent rearrangement in the presence of water to give 3H-azepinones, is performed in continuous flow in a photoreactor constructed of fluorinated ethylene polymer (FEP) tubing. Fine tuning of the

• reaction conditions using the flow reactor allowed minimization of secondary photochemical reactions. Keywords: azepinones; azides; continuous flow; nitrenes; photochemistry; Findings Although photochemical rearrangements are an important class of reactions for heterocycle synthesis [1][2], their use is

• simple to achieve by running the reactor over an extended period. Additionally, the precise control of the reaction conditions and the continuous removal of products inherent in flow systems can offer improved yields and selectivities [8][15]. Nitrenes generated by aryl azide photolysis are important