Preparation of the First Isobenzofuran Containing Two Ring Nitrogens: A New Diels - Alder Diene for the Synthesis of Molecular Scaffolds Containing One or More End-Fused 3,6-Di(2-pyridyl)pyridazine Ligands

2003 ◽  
Vol 56 (8) ◽  
pp. 811 ◽  
Author(s):  
Ronald N. Warrener ◽  
Douglas N. Butler ◽  
Davor Margetic
Keyword(s):  
Diels Alder ◽  
Molecular Scaffolds ◽  
Flash Vacuum Pyrolysis ◽  
Vacuum Pyrolysis ◽  
Ring Nitrogen ◽  
Molecular Architectures ◽  
First Time

Preparation of a stable, crystalline isobenzofuran containing two ring-nitrogen atoms, 4,7-di(2-pyridyl)-5,6-diazaisobenzofuran (diaza-IBF) (12), is reported here for the first time. Diaza-IBF was prepared using the s-tetrazine-induced fragmentation of 1,4-di(2-pyridyl)-5,8-epoxy-5,8-dihydrophthalazine (9), for which a synthesis is provided. Diaza-IBF was also prepared by flash vacuum pyrolysis (FVP) of the isomeric N-methyl-1,4-di(2-pyridyl)-5,8-epoxy-5,6,7,8-tetrahydrophthalazine-6,7-dicarboximides (18) and (19), formed in three steps from furan, N-methyl maleimide, and 3,6-di(2-pyridyl)-s-tetrazine. Diaza-IBF was employed in cycloaddition protocols with alkenes to form scaffold mono- or bis-3,6-di-(2-pyridyl)-pyridazine ligands having novel molecular architectures.

New Thermal and Photochemical Routes to Dewar Furan and Other Isomers on the C4H4O Energy Surface: the Role of Isobenzofuran as a Trapping Agent

1991 ◽  
Vol 44 (9) ◽  
pp. 1275 ◽  
Author(s):  
RN Warrener ◽  
IG Pitt ◽  
RA Russell
Keyword(s):  
High Temperatures ◽  
Low Temperatures ◽  
Energy Surface ◽  
Thermal Study ◽  
Diels Alder ◽  
Flash Vacuum Pyrolysis ◽  
Vacuum Pyrolysis ◽  
Benzene Oxide ◽  
Trapping Agent

Photolysis of the specially synthesized substrate (39) leads to quantitative fragmentation into the phthalimide (56) and Dewar furan (4a). Dewar furan has only transient existence even at -65°, yet can be trapped effectively with isobenzofuran but not furan. Rapid isomerization to cycloprop-2-enecarbaldehyde (57) occurs at the photolysis temperatures and this product is also trapped by the isobenzofuran . In the absence of trapping agent, photolysis of (39) produces some furan but no 1H n.m.r . evidence can be obtained for (4a) or (57), even at low temperatures (-85°). Separate irradiation of (57) causes extensive polymerization, without yielding other recognizable products. Furan is concluded, therefore, to arise from photoisomerization of (4a) rather than photochemical or thermal isomerization of (57). Separate thermal study of (57) shows that isomerization to furan only occurs above 420°. Flash vacuum pyrolysis of the polycyclic epoxide (72) provides a new retro- Diels-Alder route to (57) which likely proceeds via (4a) as an intermediate. At high temperatures (57) is isomerized to furan. A new Dewar benzene oxide (41) and Dewar benzene (45) are reported en route to the photosubstrates (39) and (50) respectively. Photolysis of (50) provides a high-yielding source of cyclobutadiene , which in the absence of trapping agent yields the syn-dimer (59).

Some reactions of 2-ethenyl-4,4-Ethylenedioxy-1-methylcyclohex-1-ene prepared by pyrolysis of 5,5-Ethylenedioxy-7a-methyl-4,5,6,7-tetrahydro-2H-inden-1(7aH)-one

1984 ◽  
Vol 37 (11) ◽  
pp. 2295 ◽  
Author(s):  
RFC Brown ◽  
GL Burge ◽  
DJ Collins
Keyword(s):  
High Pressures ◽  
Preparative Thin Layer Chromatography ◽  
Major Product ◽  
Diels Alder ◽  
Lewis Acid Catalysts ◽  
Flash Vacuum Pyrolysis ◽  
Vacuum Pyrolysis ◽  
Layer Chromatography ◽  
Mild Hydrolysis ◽  
Hydrolysis Of

Flash vacuum pyrolysis of 5,5-ethylenedioxy-7a-methyl-4,5,6,7-tetrahydro-2H-inden-1(7aH)-one (2) at 630� gave a good yield of 2-ethenyl-4,4-ethylenedioxy-1-methylcyclohex-1-ene (6), but at 740� p-cresol was the major product. The diene acetal (6) was also obtained by pyrolysis of 5,5-ethylene- dioxy-lβ-hydroxy-7a-methyl-1,2,5,6,7,7a-hexahydro-4H-indene-1α-carbonitrile (3) at 600�. Pyrolytic reactions of 7a-methyl-2,3,7,7a-tetrahydro-1H-indene-1,5(6H)-dione (1), 5,5-ethylenedithio-7a- methyl-2,3,5,6,7,7a-hexahydro-1H-inden-1-one (7) and of 1,1-ethylenedioxy-3,5,5-trimethylcyclohex- 3-ene (8) are also described. Mild hydrolysis of the diene acetal (6) afforded 3-ethenyl-4-methylcyclohex-3-en-1-one (9) which upon brief treatment with dry hydrogen chloride in chloroform at 0� gave, after preparative thin-layer chromatography, a low yield of pure 3-ethenyl-4-methylcyclohex-2-en-1-one (11). The diene acetal (6) failed to undergo Diels-Alder reactions, even at high pressures with Lewis acid catalysts, and it reacted anomalously with two molecules of 4-phenyl-1,2,4-triazoline-3,5-dione; the isomeric diene acetal 1-ethenyl-3,3-ethylenedioxy-6-methylcyclohex-1-ene (18) gave the expected Diels-Alder adduct with this reagent.

Flash vacuum pyrolysis of anthracenic Diels–Alder adducts, a convenient source of methanethial and methanethial S-oxide

1987 ◽  
Vol 65 (2) ◽  
pp. 290-291 ◽  
Author(s):  
Yannick Vallee ◽  
Jean-Louis Ripoll ◽  
Christophe Lafon ◽  
Geneviève Pfister-Guillouzo
Keyword(s):  
Nuclear Magnetic Resonance ◽  
Magnetic Resonance ◽  
Low Temperature ◽  
Gas Phase ◽  
Photoelectron Spectroscopy ◽  
Diels Alder ◽  
Flash Vacuum Pyrolysis ◽  
Vacuum Pyrolysis ◽  
Nuclear Magnetic

The flash vacuum pyrolysis of Diels–Alder adducts of anthracene constitutes a rapid and selective route to methanethial 1 and methanethial S-oxide 2, as analyzed in the gas phase by photoelectron spectroscopy. Low temperature infrared and nuclear magnetic resonance (1H, 13C) spectra are also reported for sulfine 2.

ChemInform Abstract: Retro-Diels-Alder Fragmentation of 2,5,6-Triphenyl-3,4- didehydropyridine Generated by Flash Vacuum Pyrolysis at 900°C.

ChemInform ◽  
2010 ◽  
Vol 23 (52) ◽  
pp. no-no
Author(s):  
R. F. C. BROWN ◽  
N. CHOI ◽  
F. W. EASTWOOD
Keyword(s):  
Diels Alder ◽  
Flash Vacuum Pyrolysis ◽  
Vacuum Pyrolysis

Methyleneketenes and methylenecarbenes. XVI. The formation of Diphenylfuran-2-ones and 3-Phenylphthalide as minor products of the pyrolysis of diphenylmethyl propiolate

1981 ◽  
Vol 34 (7) ◽  
pp. 1467 ◽  
Author(s):  
RFC Brown ◽  
FW Eastwood ◽  
N Chaichit ◽  
BM Gatehouse ◽  
JM Pfeiffer ◽  
...  
Keyword(s):  
Structure Determination ◽  
Phenyl Ring ◽  
Diels Alder ◽  
Insertion Reaction ◽  
X Ray ◽  
Flash Vacuum Pyrolysis ◽  
Methyl Propiolate ◽  
Vacuum Pyrolysis ◽  
Labelling Experiment ◽  
A Minor

The formation of a mixture of lactones as a minor product of the flash vacuum pyrolysis of diphenyl-methyl propiolate (1) has been investigated further. ��� The diphenylfuran-2-ones (3), (4), and (5) are shown to be formed through an intramolecular insertion reaction of the methylenecarbene (2), formed from (1) at 640°, which leads to 5,5-diphenyl-furan-2(5H)- one (3) as the primary product. ��� 3-Phenylphthalide (8) is apparently formed by intramolecular Diels-Alder addition of the C≡C bond of (1) to one phenyl ring which acts as the diene component, followed by loss of acetylene from an intermediate barrelene derivative (10). This is confirmed by a deuterium labelling experiment. ��� 1-Phenyl-2-benzoxepin-3(1H)-one (7), considered at first as a possible intermediate in the pyrolysis of (1), is synthesized in six steps from 2-aminobenzophenone, and its X-ray structure determination is reported. On pyrolysis at 640°/0.07 mm (7) decarbonylates smoothly to give 2-vinylbenzophenone.

Maleimide-Fused Cyclobutadienes and Dewar Furans: Trapping With Dienes as a Route to Propellane Photosubstrates With Potential for Oxiren Production

1995 ◽  
Vol 48 (2) ◽  
pp. 241 ◽  
Author(s):  
RN Warrener ◽  
GM Elsey ◽  
IG Pitt ◽  
RA Russell
Keyword(s):  
Direct Observation ◽  
Titanium Tetrachloride ◽  
Reactive Intermediates ◽  
Alder Reaction ◽  
Diels Alder ◽  
Am1 Calculations ◽  
Cycloaddition Reactions ◽  
Flash Vacuum Pyrolysis ◽  
Diels Alder Reaction ◽  
Vacuum Pyrolysis

N-Methylmaleimide-fused cyclobutadiene (15) and its 1,2-dimethyl derivative (41) have been generated by zinc/titanium tetrachloride treatment of the vicinal dibromide (39) and (24) respectively. Prior epoxidations of (24) and (39) produce mixtures of dibromo epoxides which yield the related N-methylmaleimide-fused Dewar furans (16) and (17) upon similar debromination (Zn/TiCl4). None of these reactive intermediates is sufficiently stable for direct observation, but each was trapped in adduct form by Diels-Alder reaction with furan. Attempts to form fused Dewar furan (17) by flash vacuum pyrolysis of the furan adduct (34) led to the production of the isomeric furo [3,4-c] pyrrole (43), the structure of which was confirmed by separate synthesis. Stereochemical assignments have been made to most adducts, and AM1 calculations have been used to predict the stereoselectivities and facial selectivities in these cycloaddition reactions. Reaction of these Dewar furans with cyclopentadienones produced propellanes which were decarbonylated to their respective cyclohexadienes and used as photosubstrates for the generation of oxiren or dimethyloxiren . Attempts to trap oxiren, generated by photolysis of propellane (12), with isobenzofuran were unsuccessful.

Methyleneketenes and methylenecarbenes. XI. Rearrangements of cycloalkylidenecarbenes

1978 ◽  
Vol 31 (2) ◽  
pp. 327 ◽  
Author(s):  
GJ Baxter ◽  
RFC Brown
Keyword(s):  
Diels Alder ◽  
Ring Size ◽  
Meldrum's Acid ◽  
Meldrum’S Acid ◽  
Flash Vacuum Pyrolysis ◽  
Vacuum Pyrolysis

The products of flash vacuum pyrolysis of the cycloalkylidene derivatives (3) of Meldrum's acid at 480-640° are rationalized in terms of formation of the cycloalkylidenecarbenes (1; ring size n = 4-8)and their rearrangement to cycloalkynes, to bicyclic cyclopropenes (e.g. (7)), or to further products derived from these. Pyrolysis of the 3,3-dimethylcyclobutylidene derivative (3h) gave 3,5-dimethylphenol, probably formed by cyclization of the (Z)-hexatrienone (22). ��� The tetrahydrofuran-3-ylidene derivative (3i) gave butatriene and formaldehyde as major products of pyrolysis; these may be formed by retro-Diels-Alder fission of the heterocycloalkyne (27).

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