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

• stepwise mechanisms may compete. Keywords: coarctate reaction; fragmentation; matrix isolation; photolysis; pyrolysis; spiroketal; Introduction Pericyclic reactions, according to the original definition, are characterized by a cyclic array of bond making and bond breaking [1][2][3]. At each atom

• . Relative to [CO2] = 1.0, the concentrations of the other pyrolysis products are as follows: [CO] = 27.2, [IN] = 3.8, [ET] = 15.9, [BC] = 11.4, [XY] = 1.3, [AA] = 3.9 [25]. Formaldehyde is formed as a minor product only. The photochemistry of ketals 2 and 3 was investigated as well by matrix isolation

• thermal coarctate fragmentation competes with stepwise processes. Experimental General: Matrix-isolation experiments were performed using standard matrix-isolation techniques [34]. For sample deposition, the slow-spray-on technique was used. Sample temperatures for deposition were ambient temperature (1

Ring opening of 2-aza-3-borabicyclo[2.2.0]hex-5-ene, the Dewar form of 1,2-dihydro-1,2-azaborine: stepwise versus concerted mechanisms

• Holger F. Bettinger and
• Otto Hauler

Beilstein J. Org. Chem. 2013, 9, 761–766, doi:10.3762/bjoc.9.86

• -azaborine (4), a boron-nitrogen heterocycle that is isoelectronic and isosteric with benzene [15], results in its Dewar isomer 2-aza-3-borabicyclo[2.2.0]hex-5-ene (3) under the conditions of cryogenic noble gas matrix isolation [16]. Under these experimental conditions (T < 35 K), the isomerisation back to

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

• ) formation of the ylide 26 and hence the ketenimine 27 becomes the dominant reaction under the conditions of matrix photolysis. Experimental General The apparatus and procedures for preparative FVT [18] and for Ar matrix isolation [11][19][20] were as previously described. KBr and CsI windows were used for

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

• nitrile ylide 47. Matrix photolysis of 2-phenyl-3-azidoquinoline (44) revealed a reversible photochemical interconversion of the benzodiazacycloheptatetraene 46 and the nitrile ylide 47. Experimental General The apparatus and procedures for preparative FVT [31] and for Ar matrix isolation [11][32][33

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

• 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

• of triazide 11 may give three triplet nitrenes 12–14, three quintet dinitrenes 15–17, and septet trinitrene 18. So far, no attempt was undertaken to discriminate such structurally alike isomers as quintet dinitrenes 16 and 17. In the present work, we report on matrix isolation and EPR studies of high

New reactive intermediates in organic chemistry

• Götz Bucher

Beilstein J. Org. Chem. 2013, 9, 613–614, doi:10.3762/bjoc.9.67

• , product studies can even yield accurate values for the kinetics of intermolecular quenching reactions of reactive intermediates. More recent techniques to characterise reactive intermediates include matrix isolation spectroscopy, where a reactive intermediate is generated in a cryogenic noble-gas matrix

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

• [1,2]hydrogen tunneling from the hydroxy group to the carbene center. Dihydroxycarbene (a) [15] and methoxyhydroxycarbene (c) [15], however, do not undergo [1,2]H-tunneling under the same conditions: Their respective products, formic acid (b) and methyl formate (d) were not detected in matrix isolation

Trapping evidence for the thermal cyclization of di-(o-acetylphenyl)acetylene to 3,3'-dimethyl- 1,1'-biisobenzofuran

• Charles P. Casey,
• Neil A. Strotman and
• Ilia A. Guzei

Beilstein J. Org. Chem. 2005, 1, No. 18, doi:10.1186/1860-5397-1-18

• to alk-2-en-4-yn-1-ones (Scheme 10). These ring openings have been studied both experimentally by matrix isolation spectroscopy [22][23] and computationally [24][25] and are described as involving coarctate transition states.[26] The transformation of 1 to A can be viewed as a coarctate ring closure