On the Thermally Induced Rearrangement of 2-Alkoxypyridines to N-alkylpyridones

2003 ◽  
Vol 56 (9) ◽  
pp. 913 ◽  
Author(s):  
Troy Lister ◽  
Rolf H. Prager ◽  
Michael Tsaconas ◽  
Kerry L. Wilkinson
Keyword(s):  
Transition State ◽  
Condensed Phase ◽  
Vapour Phase ◽  
Thermally Induced ◽  
Flash Vacuum Pyrolysis ◽  
Structural Assignment ◽  
Vacuum Pyrolysis

Analogues of 2-methoxypyridine undergo rearrangement to N-methylpyridones under flash vacuum pyrolysis (FVP) conditions. Ethoxy derivatives undergo competitive ethyl migration and elimination of ethylene. Analogues of 4-methoxypyridine do not undergo rearrangement under FVP conditions, but demethylation on silica may occur. The ease of rearrangement follows the basicity of the alkoxyhetarene to some extent. The vapour-phase rearrangements have been contrasted to condensed-phase pyrolyses, and a four-centre transition state for the former is supported by computation. The rearrangement allows structural assignment to the two products from the reaction of 2,4-dichloroquinoline with pyrrolidine.

Ethynamine - Ketenimine - Acetonitrile - Rearrangements: A computational Study of Flash Vacuum Pyrolysis Processes

2017 ◽  
Author(s):  
Curt Wentrup ◽  
Didier Begue ◽  
Regis Leung-Toung
Keyword(s):  
Transition State ◽  
Radical Pair ◽  
Computational Study ◽  
Physical Reality ◽  
Second Step ◽  
Flash Vacuum Pyrolysis ◽  
Vacuum Pyrolysis ◽  
Experimental Shock ◽  
Very High ◽  
Concerted Reaction

<p>The rearrangements of ethynamine <b>3</b> (H-CºC-NH<sub>2</sub>) to ketenimine <b>4</b> (CH<sub>2</sub>=C=NH) and acetonitrile <b>5</b> (CH<sub>3</sub>CN) were investigated computationally up to the MP4(SDTQ)/6-31G*//MP2(FU)/6-31G* level. The calculated barrier for a concerted reaction <b>3</b> -> <b>4</b> is very high, 74 kcal/mol, the structure of the transition state very unusual, and this path is discredited. A lower barrier of about 60 kcal/mol via aminovinylidene <b>2</b> and imidoylcarbene <b>15</b> has been found. The calculated barrier for a concerted second step <b>4 </b>-><b> 5</b> is 61 kcal/mol, and the transition state structure is again very unusual with a virtually linear CCN backbone, but this does not appear to correspond to physical reality. Instead, CASPT2 calculations predict reaction via vinylnitrene <b>9</b> and/or homolysis of <b>4 </b>to the radical pair ·CH<sub>2</sub>CN + H· (<b>11</b>) with a barrier of 67-70 kcal/mol in agreement with experimental shock-tube data. Recombination (maybe via roaming) affords acetonitrile <b>5</b>. There is strong experimental evidence for homolytic paths in pas-phase pyrolyses of ketenimines.</p>

Synthesis of Heterocyclic-fused Imidazoles by Pyrolysis of N-Heterocyclic Isoxazol-5(2H)-ones

2014 ◽  
Vol 67 (9) ◽  
pp. 1228 ◽  
Author(s):  
Steven-Alan G. Abel ◽  
Mathew O. Eglinton ◽  
James K. Howard ◽  
Dylan J. Hunt ◽  
Rolf H. Prager ◽  
...  
Keyword(s):  
Condensed Phase ◽  
Synthesis Method ◽  
Structural Rearrangements ◽  
Flash Vacuum Pyrolysis ◽  
Vacuum Pyrolysis

The synthesis of heterocyclic-fused imidazoles was achieved by flash vacuum pyrolysis (FVP) of N-heterocyclic isoxazol-5(2H)-ones via an iminocarbene intermediate. Unlike iminocarbenes generated from triazoles, no structural rearrangements were observed during the current synthesis method. We also demonstrated that less volatile isoxazol-5(2H)-one derivatives yield the corresponding imidazoles by condensed phase pyrolysis.

Ethynamine - Ketenimine - Acetonitrile - Rearrangements: A computational Study of Flash Vacuum Pyrolysis Processes

2017 ◽  
Author(s):  
Curt Wentrup ◽  
Didier Begue ◽  
Regis Leung-Toung
Keyword(s):  
Transition State ◽  
Radical Pair ◽  
Computational Study ◽  
Physical Reality ◽  
Second Step ◽  
Flash Vacuum Pyrolysis ◽  
Vacuum Pyrolysis ◽  
Experimental Shock ◽  
Very High ◽  
Concerted Reaction

<p>The rearrangements of ethynamine <b>3</b> (H-CºC-NH<sub>2</sub>) to ketenimine <b>4</b> (CH<sub>2</sub>=C=NH) and acetonitrile <b>5</b> (CH<sub>3</sub>CN) were investigated computationally up to the MP4(SDTQ)/6-31G*//MP2(FU)/6-31G* level. The calculated barrier for a concerted reaction <b>3</b> -> <b>4</b> is very high, 74 kcal/mol, the structure of the transition state very unusual, and this path is discredited. A lower barrier of about 60 kcal/mol via aminovinylidene <b>2</b> and imidoylcarbene <b>15</b> has been found. The calculated barrier for a concerted second step <b>4 </b>-><b> 5</b> is 61 kcal/mol, and the transition state structure is again very unusual with a virtually linear CCN backbone, but this does not appear to correspond to physical reality. Instead, CASPT2 calculations predict reaction via vinylnitrene <b>9</b> and/or homolysis of <b>4 </b>to the radical pair ·CH<sub>2</sub>CN + H· (<b>11</b>) with a barrier of 67-70 kcal/mol in agreement with experimental shock-tube data. Recombination (maybe via roaming) affords acetonitrile <b>5</b>. There is strong experimental evidence for homolytic paths in pas-phase pyrolyses of ketenimines.</p>

Sulfonyl isocyanides RSO2NC

2017 ◽  
Author(s):  
Curt Wentrup ◽  
Horst Briehl
Keyword(s):  
Ir Spectrum ◽  
Reaction Conditions ◽  
Flash Vacuum Pyrolysis ◽  
Vacuum Pyrolysis

Flash vacuum pyrolysis (FVP) of 5-azido-1-aryltetrazoles results in triple N<sub>2</sub> elimination and formation of aryl isocyanides RNC, which rearrange in part to aroylnitriles RCN under the reaction conditions. Similar FVP of 5-azido-1-arenesulfonyltetrazoles generates a compound absorbing in the IR spectrum (77 K) at 2090 cm<sup>-1 </sup>and assigned the structure of arenesulfonyl isocyanide, ArSO<sub>2</sub>NC <b>11</b>. FVP at temperatures above 600 <sup>o</sup>C results in progressively more nitrile ArSO<sub>2</sub>CN <b>12</b>. Compound <b>11</b> also disappears on warming above -80 <sup>o</sup>C

Sulfonyl isocyanides RSO2NC

2017 ◽  
Author(s):  
Curt Wentrup ◽  
Horst Briehl
Keyword(s):  
Ir Spectrum ◽  
Reaction Conditions ◽  
Flash Vacuum Pyrolysis ◽  
Vacuum Pyrolysis

Flash vacuum pyrolysis (FVP) of 5-azido-1-aryltetrazoles results in triple N<sub>2</sub> elimination and formation of aryl isocyanides RNC, which rearrange in part to aroylnitriles RCN under the reaction conditions. Similar FVP of 5-azido-1-arenesulfonyltetrazoles generates a compound absorbing in the IR spectrum (77 K) at 2090 cm<sup>-1 </sup>and assigned the structure of arenesulfonyl isocyanide, ArSO<sub>2</sub>NC <b>11</b>. FVP at temperatures above 600 <sup>o</sup>C results in progressively more nitrile ArSO<sub>2</sub>CN <b>12</b>. Compound <b>11</b> also disappears on warming above -80 <sup>o</sup>C

The Pyrolytic Rearrangement of 1-Alkynoyl-3-methylpyrazoles: Synthesis of Pyrazolo[1,5-a]pyridin-5-ols and Related Compounds

1994 ◽  
Vol 47 (6) ◽  
pp. 991 ◽  
Author(s):  
RFC Brown ◽  
FW Eastwood ◽  
GD Fallon ◽  
SC Lee ◽  
RP Mcgeary
Keyword(s):  
Carbon Chain ◽  
Ring Structure ◽  
High Yield ◽  
Methyl Group ◽  
X Ray ◽  
X Ray Crystallography ◽  
Flash Vacuum Pyrolysis ◽  
Vacuum Pyrolysis ◽  
Fused Ring ◽  
Related Compounds

Flash vacuum pyrolysis of 1-(alkyn-2′-oyl)-3-methylpyrazoles at 650°/0.03 mm forms pyrazolo[1,5-a]pyridin-5-ols, often in high yield, which may bear substituents at C2, C3 or C7. In the absence of a 3-methyl group in the precursor, N-ethynylpyrazoles are formed in low yield. The formation of both types of product is interpreted as involving 3-(N-pyrazolyl)propadienones formed by N1 → N2 migration of the N-alkynoyl group with inversion of the three-carbon chain. The fused-ring structure of 2-methylpyrazolo[1,5-a]pyridin-5-ol (25) was established by X-ray crystallography of the O-benzoyl derivative (27).

Preparation of benzocyclobutenes by flash vacuum pyrolysis

1978 ◽  
Vol 19 (46) ◽  
pp. 4569-4572 ◽  
Author(s):  
Peter Schiess ◽  
Markus Heitzmann ◽  
Suzanne Rutschmann ◽  
René Stäheli
Keyword(s):  
Flash Vacuum Pyrolysis ◽  
Vacuum Pyrolysis
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