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

• ]pyrazine (24). FVT of 4-azidopyridine (18) as well as of 24 or 2-(5-tetrazolyl)pyrazine (23) affords the products expected from the nitrene, i.e., 4,4’-azopyridine and 2- and 3-cyanopyrroles. Matrix photolyses of both 18 and 24 result in ring expansion of 4-pyridylnitrene/2-pyrazinylcarbene to 1,5

• -diazacyclohepta-1,2,4,6-tetraene (20). Further photolysis causes ring opening to the ketenimine 27. Keywords: carbene–nitrene interconversion; diazepines; flash vacuum thermolysis; matrix photochemistry; nitrile ylides; reactive intermediates; Introduction The carbene–nitrene interconversion exemplified with

• vacuum thermolysis (FVT) conditions cyanocyclopentadiene 6 is formed (Scheme 1). Several other carbene–nitrene rearrangements have been reported [3][4][5]. In addition to the ring expansion (1–2–3), two ring opening reactions have been investigated in recent years. Type I ring opening takes place in

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

• propargylic structures, and for this reason their cumulene-type IR absorptions can occur over a wide frequency range, 1900–2300 cm−1, depending on substituents. The IR absorption of 11 was observed at 1961 cm−1, indicating an allenic structure. Nitrene 10 can also undergo ring expansion to two

• the (s,Z)-nitrile ylide 11 lies 5 kcal/mol above the open shell singlet nitrene S1 10, i.e., the barrier is only 11 kcal/mol above the cyclic ketenimine 16. This is lower than the barrier for direct ring opening of the nitrene 10 itself (16 kcal/mol) (Scheme 4 and Figure 1) [13]. Thus, while both the

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

• the nitrene C–N bonds and different Mulliken spin populations on the nitrene units (Table 1). Theoretically, such asymmetric trinitrenes should show rather large ES values [30]. Nevertheless, the ES value of trinitrene 18 is even smaller than that of C2v symmetric trinitrene 6c [31]. DFT calculations

• connecting the nitrene units in positions 2 and 6 of the pyridine ring and were parallel to the DZZSO axis of the spin–orbit tensor DSO connecting two heavy chlorine atoms in positions 3 and 5 of the pyridine ring [30]. In the case of trinitrene 18, the DZZSO axis of the spin-orbit tensor DSO almost

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

• peptides have successfully been used to generate biocompatible materials [10][11]. Conceptually, we planned to first functionalize the hydrocarbon TPX 2 via UV-mediated nitrene insertion to form polymer derivative 4 (Scheme 1) [12][13][14]. Therefore, nitrene precursor 3 was modified with an oligo(ethylene

• 2 with a methanolic solution of nitrene precursor 3, and then drying followed by UV irradiation (Hg lamp, 254 nm) initially did not lead to surface modification. The presence of F and N on the TPX membrane was not detectable by XPS analysis. The photoinduced reaction of azide 3 with cyclohexane

• insertion of the nitrene moiety. Irradiation with UV light at 312 nm clearly showed absorption generated from the π-system of the fluorinated phenyl ring (Figure 2). In contrast to this, nonfunctionalized foils did not show any absorption. X-ray photoelectron spectroscopy (XPS) analysis of functionalized

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

• the reactivity of a related iridium(I) carbene system, supported by Ozerov's amidophosphine pincer ligand and generated by multiple C–H activations [18][68][69][70], with a number of heterocumulenes such as those described above. Oxygen-atom, sulfur-atom, and nitrene-group transfers to the carbene

• -atom or nitrene-group transfer and formation of (PNP)Ir–N2 [78], and this reaction was utilized in catalytic C–H functionalization (see below). More recently, Hillhouse's nickel carbenes and imides have been shown to exhibit similar reactivity with organic azides, though reaction with CO2 has not been

• carbene or nitrene (Scheme 13a). This would be formally related to carbene or nitrene insertions that have been shown to occur, among other cases, at dirhodium paddlewheel complexes [85], though the specific mechanism of C–H bond breaking (and hence the reaction selectivity) would be quite different. Such

An intramolecular inverse electron demand Diels–Alder approach to annulated α-carbolines

• Zhiyuan Ma,
• Feng Ni,
• Grace H. C. Woo,
• Sie-Mun Lo,
• Philip M. Roveto,
• Scott E. Schaus and
• John K. Snyder

Beilstein J. Org. Chem. 2012, 8, 829–840, doi:10.3762/bjoc.8.93

• roles of the benzene and pyridine rings, with the former as the nucleophile and latter as electrophile through the diazonium salt, led to improved yields in the indole ring closure [41], as did microwave promotion of the original methodology [42]. Nitrene insertion chemistry of appropriately substituted

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

• tools, both for preparative heterocycle synthesis [16][17] and for photoaffinity labeling of proteins [18][19][20]. The photolysis of aryl azide 1 [21], a well-studied and widely used reaction [22][23][24][25][26][27][28][29][30], generates the singlet aryl nitrene intermediate 12 (Scheme 1). Ring

En route to photoaffinity labeling of the bacterial lectin FimH

• Thisbe K. Lindhorst,
• Michaela Märten,
• Andreas Fuchs and
• Stefan D. Knight

Beilstein J. Org. Chem. 2010, 6, 810–822, doi:10.3762/bjoc.6.91

•  2a) for photolabeling of the bacterial lectin FimH [15]. They differ in their photoactive functional groups, which are part of the aglycone moiety. Upon irradiation, the aryl azide 1 and the diazirine 2 expel nitrogen to yield a reactive nitrene and a carbene intermediate, respectively. Irradiation

Benzyne arylation of oxathiane glycosyl donors

• Martin A. Fascione and
• W. Bruce Turnbull

Beilstein J. Org. Chem. 2010, 6, No. 19, doi:10.3762/bjoc.6.19

• -workers (Scheme 2) [25][26][27][28]. The low reaction temperature was expected to be compatible with stereoselective glycosylation. Following the reaction of 1-ABT (8) with lead tetraacetate, benzyne (9) formation is believed to occur via degradation of either an N-nitrene intermediate 10 or an N-acetate

Mitomycins syntheses: a recent update

• Jean-Christophe Andrez

Beilstein J. Org. Chem. 2009, 5, No. 33, doi:10.3762/bjoc.5.33

• gives rise to complex reaction mixtures due to the possibility of nitrene insertion. Cycloaddition of phenyl azide, however, to the unsaturated carbonyl 41 was readily accomplished to give triazoline 42 in 56% yield (Scheme 10) [53][54][55]. According to this scheme, the allylic alcohol 38 was oxidized

• -dimethoxyhydroquinone was then oxidized with silver(II) pinacolate (in poor yield) to give mitomycin K. 3.2. Naruta, Maruyama. Azide cycloaddition From a synthetic point of view, the intramolecular [1+4] cyclisation of a nitrene with a dienyl moiety gives a pyrrolizidine, the key structure found in mitomycins and many

• by attack of the quinone by an intermediate nitrene via intermediates 52 and 53 (Scheme 14) [60]. The diastereoselectivity observed during the cycloaddition originated from the most favored staggered conformation in the transition state based on the Houk model, wherein the allylic hydrogen is

Synthesis of sulfonimidamides from sulfinamides by oxidation with N-chlorosuccinimide

• Olga García Mancheño and
• Carsten Bolm

Beilstein J. Org. Chem. 2007, 3, No. 25, doi:10.1186/1860-5397-3-25

• sulfonamides, in which one oxygen has been replaced by a nitrogen group. They are known since 1962,[1] and a number of recent investigations focussed on both their reactivity and application in organic synthesis, such as nitrogen sources for metal-catalyzed nitrene transfer reactions, [2][3][4][5] and their