Come-back of phenanthridine and phenanthridinium derivatives in the 21st century

• Lidija-Marija Tumir,
• Marijana Radić Stojković and
• Ivo Piantanida

Beilstein J. Org. Chem. 2014, 10, 2930–2954, doi:10.3762/bjoc.10.312

• pyrolysis of the condensation product of benzaldehyde and aniline [6]. The reaction conditions were improved by Morgan and Walls, based on a reaction including a cyclization of phenanthridine by dehydrative ring-closure with phosphorus oxychloride in boiling nitrobenzene [7]. Over the 20th century this

Expedient synthesis of 1,6-anhydro-α-D-galactofuranose, a useful intermediate for glycobiological tools

• Luciana Baldoni and
• Carla Marino

Beilstein J. Org. Chem. 2014, 10, 1651–1656, doi:10.3762/bjoc.10.172

• starts from a galactofuranose (D-Galf) template conveniently derivatized. Pioneer procedures for the synthesis of 2 involved the pyrolysis of D-Gal under reduced pressure [11][12] and the acid treatment under heating [13], with the subsequent tedious separation from several byproducts, including the

Site-selective covalent functionalization at interior carbon atoms and on the rim of circumtrindene, a C₃₆H₁₂ open geodesic polyarene

• Hee Yeon Cho,
• Ronald B. M. Ansems and
• Lawrence T. Scott

Beilstein J. Org. Chem. 2014, 10, 956–968, doi:10.3762/bjoc.10.94

• the authors’, have been particularly successful in synthesizing geodesic polyarenes using flash vacuum pyrolysis (FVP) [6]. The FVP method involves slow sublimation of a starting material under vacuum, rapid passage of the gas-phase molecules through a hot zone, and subsequent capture of the products

• circumtrindene (6), one of the most highly-curved fullerene fragments known, comprising 60% of the C60 ball. Results and Discussion Synthesis and properties of circumtrindene (6) In 1996, our laboratory reported that the C36H12 bowl circumtrindene (6) could be obtained by flash vacuum pyrolysis of decacyclene

Recent applications of the divinylcyclopropane–cycloheptadiene rearrangement in organic synthesis

• Sebastian Krüger and
• Tanja Gaich

Beilstein J. Org. Chem. 2014, 10, 163–193, doi:10.3762/bjoc.10.14

• detected in the human body after cocaine consumption. It can be degradatively accessed from cocaine through pyrolysis, cocaine congeners can be prepared via conjugate addition afterwards [113][114]. Boc-protected pyrrole 127 was subjected to rhodium-catalyzed cyclopropanation with vinyldiazo compound 128

An overview of the synthetic routes to the best selling drugs containing 6-membered heterocycles

• Marcus Baumann and
• Ian R. Baxendale

Beilstein J. Org. Chem. 2013, 9, 2265–2319, doi:10.3762/bjoc.9.265

• sequence via the corresponding 2-pyrone (e.g. Scheme 9), which is converted to the 2-pyridone through an exchange with ammonia or an equivalent nitrogen source (NH4X; X = Cl, Br, I, OAc, OH). However, more conveniently the 2-pyrone precursor can be generated via the vacuum pyrolysis of coumalic acid (1.56

A practical synthesis of long-chain iso-fatty acids (iso-C₁₂–C₁₉) and related natural products

• Mark B. Richardson and
• Spencer J. Williams

Beilstein J. Org. Chem. 2013, 9, 1807–1812, doi:10.3762/bjoc.9.210

• the terminal alkene of methyl undecylenate (available as a pyrolysis product of ricinoleic acid) using isopropyl chloroformate and ethyldichloroaluminium [51], and the synthesis of the iso-C17 acid 6 from methyl ustilate (15,16-dihydroxypalmitate) [52]. Despite the interest in natural products

The preparation of several 1,2,3,4,5-functionalized cyclopentane derivatives

• André S. Kelch,
• Peter G. Jones,
• Ina Dix and
• Henning Hopf

Beilstein J. Org. Chem. 2013, 9, 1705–1712, doi:10.3762/bjoc.9.195

• are involved that employ β-elimination processes – be it of halides, aminoxide derivatives (Cope elimination), acetates (ester pyrolysis), etc. [2][3]. When starting with derivatives of type 6 it should be noted that these compounds can exist in the form of different diastereomers; for example – as

• be subjected to flash vacuum pyrolysis (Scheme 4). Whereas all our attempts to synthesize 20 failed (see Supporting Information File 1), the pentaester 21 was obtained under standard conditions from 16 by treatment with excess acetyl chloride in excellent yield; its spectroscopic data can be found in

Thermochemistry and photochemistry of spiroketals derived from indan-2-one: Stepwise processes versus coarctate fragmentations

• Götz Bucher,
• Gernot Heitmann and
• Rainer Herges

Beilstein J. Org. Chem. 2013, 9, 1668–1676, doi:10.3762/bjoc.9.191

• we investigate the fragmentation reactions of cyclic ketals. Three ketals with different ring sizes derived from indan-2-one were decomposed by photolysis and pyrolysis. Particularly clean is the photolysis of the indan-2-one ketal 1, which gives o-quinodimethane, carbon dioxide and ethylene. The

• mechanism formally corresponds to a photochemically allowed coarctate fragmentation. Pyrolysis of the five-ring ketal yields a number of products. This is in agreement with the fact that coarctate fragmentation observed upon irradiation would be thermochemically forbidden, although this exclusion principle

• does not hold for chelotropic reactions. In contrast, fragmentation of the seven-ring ketal 3 is thermochemically allowed and photochemically forbidden. Upon pyrolysis of 3 several products were isolated that could be explained by a coarctate fragmentation. However, the reaction is less clean and

A Lewis acid-promoted Pinner reaction

• Dominik Pfaff,
• Gregor Nemecek and
• Joachim Podlech

Beilstein J. Org. Chem. 2013, 9, 1572–1577, doi:10.3762/bjoc.9.179

• with amines furnishes amidinium compounds and the reaction with alcohols gives rise to ortho esters. A less frequently used pyrolysis leads to carboxamides (Scheme 3) [3][4][5]. The harsh reaction conditions preclude a broad application of the Pinner reaction. The high toxicity and the laborious

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

• . 1 mbar due to a shock wave induced by rapid distillation of the azide into the furnace under high vacuum, results in ring contraction to cyanocyclopentadiene 6 [12]. Similar pyrolysis of 4-azidopyridine results in ring contraction to a mixture of 2- and 3-cyanopyrroles 16 and 17. Because the ring

• pyrolysis tube. The exact mechanisms of ring contraction in arylnitrenes are under investigation, but in the case of 2-pyridylnitrene (Scheme 2) three routes to the cyanopyrroles have been described [10], as has their thermal interconversion [9][10]. The analogous, concerted ring contraction of

• 2076 cm−1 (Figure 1). Warming the neat diazo compound to ca. −30 °C causes ring closure to triazole 24. Compound 24 can be isolated in up to 20% yield in preparative pyrolysis of 23 [16]. Further FVT of either 23 or 24 at ≥450 °C/10−3 mbar results in the formation of approximately equal amounts of the

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

• triazoloquinazoline 53 undergo pyrolysis via the diazomethylquinazoline 54 (Scheme 13) [23]. Both afforded the 3-cyanoindole 48 in nearly quantitative yield (up to 98%) on FVT at 400–600 °C, but no traces of either indoloquinoline 50 or the 3-aminoquinoline 51 were detectable. The same was true when the thermolysis

• pyrolysis tube at 170 °C and pyrolysed at 600 °C/10−3 mbar in the course of 12 h. The resulting pyrolysate (120 mg) was identified as a 1:1 mixture of 2- and 3-cyanopyrroles 7 and 8 by comparison of the 1H NMR, IR and mass spectra with those of authentic materials. Yields were determined by GC as above [10

Photoionisation of the tropyl radical

• Kathrin H. Fischer,
• Patrick Hemberger,
• Andras Bodi and
• Ingo Fischer

Beilstein J. Org. Chem. 2013, 9, 681–688, doi:10.3762/bjoc.9.77

• study on the photoionisation of the cycloheptatrienyl (tropyl) radical, C7H7, using tunable vacuum ultraviolet synchrotron radiation. Tropyl is generated by flash pyrolysis from bitropyl. Ions and electrons are detected in coincidence, permitting us to record mass-selected photoelectron spectra. The

• efficient source for tropyl radicals generated by pyrolysis. Furthermore, the ground and excited states of the ion have been investigated computationally [9][17]. In the present study we extend the previous work using imaging photoelectron–photoion coincidence (iPEPICO) techniques in combination with VUV

• situ detection of radicals in flames by photoionisation [30]. The goal of the present experimental study was to elucidate the vibrational structure of the tropyl ion ground state with threshold photoelectron spectroscopic (TPES) techniques. Results and Discussion The performance of the pyrolysis source

The chemistry of bisallenes

• Henning Hopf and
• Georgios Markopoulos

Beilstein J. Org. Chem. 2012, 8, 1936–1998, doi:10.3762/bjoc.8.225

• pyrolysis reaction (see Section 5). How fast a very large structural variety can be generated from these basic patterns, becomes obvious if one realizes that, for example, in the aromatic systems 12, the allene units can be anchored also in meta- and/or para-position and condensed aromatic compounds or

• superior route to 88 consists of the thermal isomerization of hexakis(trimethylsilyl)benzene (89) [71][72]. Under flash vacuum pyrolysis conditions (400 °C, <0.01 Tor) 88 is produced from 89 as a mixture with several of its isomers (see below), but heating of the aromatic substrate at 200 °C for 10 h

• -shift to provide the diradical intermediate 90. In the next step the ring is split to furnish derivative 91, which, by another TMS-shift, isomerizes to the propargylallene 92. The sequence ends with still another TMS-relocation to provide the final product 88. Both, 91 and 92 are pyrolysis products

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

• the pyrolysis of proteins [10][11] as well as the pyrolysis of tryptophan [12]. Isoeudistomin U, isolated from the ascidian Lissoclinum fragile, was originally reported to have an α-carboline skeleton [13], but this assignment was later shown to be incorrect [14]. Given their isomeric relationship to

Valence isomerization of cyclohepta-1,3,5-triene and its heteroelement analogues

• Helen Jansen,
• J. Chris Slootweg and
• Koop Lammertsma

Beilstein J. Org. Chem. 2011, 7, 1713–1721, doi:10.3762/bjoc.7.201

• -triene [14]. Besides the 1–2 interconversion, the C7H8 system is rich in rearrangements (Scheme 3). In 1957, Woods found that bicyclo[2.2.1]hepta-2,5-diene (12) converts to cycloheptatriene (1), which was postulated to proceed via diradical 11 and norcaradiene (2) [28]. Instead, pyrolysis of 1 yielded

Synthesis of fluoranthenes by hydroarylation of alkynes catalyzed by gold(I) or gallium trichloride

• Sergio Pascual,
• Christophe Bour,
• Paula de Mendoza and
• Antonio M. Echavarren

Beilstein J. Org. Chem. 2011, 7, 1520–1525, doi:10.3762/bjoc.7.178

• have already been synthesized by palladium-catalyzed arylation reactions [53][54]. Strategically halogenated decacyclenes with a substitution pattern similar to that of 2 have been used for the synthesis of circumtrindene by flash vacuum pyrolysis [55]. Here we report the results on the synthesis of

Advances in synthetic approach to and antifungal activity of triazoles

• Kumari Shalini,
• Nitin Kumar,
• Sushma Drabu and
• Pramod Kumar Sharma

Beilstein J. Org. Chem. 2011, 7, 668–677, doi:10.3762/bjoc.7.79

• nitrogen atoms. However, flash vacuum pyrolysis at 500 °C leads to loss of molecular nitrogen (N2) to produce aziridine. Certain triazoles are relatively easy to cleave by ring–chain tautomerism. Synthesis of triazoles Substituted 1,2,3-triazoles can be produced by the azide–alkyne Huisgen cycloaddition in

Reciprocal polyhedra and the Euler relationship: cage hydrocarbons, C_nH_n and closo-boranes [B_xH_x]²⁻

• Michael J. McGlinchey and
• Henning Hopf

Beilstein J. Org. Chem. 2011, 7, 222–233, doi:10.3762/bjoc.7.30

• achieved via preparative-scale flash vacuum pyrolysis [23]. The icosahedral point group possesses ten C3 axes and six C5 axes, and synthetic proposals have taken advantage of both types of symmetry elements. The former prompted Woodward [24] and Jacobson [25] independently from each other to suggest that

Intramolecular hydroxycarbene C–H-insertion: The curious case of (o-methoxyphenyl)hydroxycarbene

• Dennis Gerbig,
• David Ley,
• Hans Peter Reisenauer and
• Peter R. Schreiner

Beilstein J. Org. Chem. 2010, 6, 1061–1069, doi:10.3762/bjoc.6.121

• experimentally by means of high vacuum flash pyrolysis (HVFP) and subsequent matrix isolation: (o-Methoxyphenyl)glyoxylic acid gives non-isolable (o-methoxyphenyl)hydroxycarbene upon pyrolysis at 600 °C, which rapidly inserts into the methyl C–H bond. The insertion product, 2,3-dihydrobenzofuran-3-ol, was

• , VII, VIII, and X elements [2][3][4][5][6][7][8][9][10][11][12] it was only very recently that free hydroxycarbenes were generated by high vacuum flash pyrolysis (HVFP) followed by immediate matrix isolation and thoroughly characterized by means of IR- and UV-spectroscopy [13][14][15]. Very

• dioxide from (o-methoxyphenyl)glyoxylic acid (6) by HVFP and subsequent condensation and isolation of the pyrolysis products in an excess of Ar (Scheme 3). However, neither 5 nor its tunneling product, o-anisaldehyde (7), could be detected: Comparison with an authentic spectrum of matrix-isolated 7 showed