2-pyridylnitrene and 3-pyridazylcarbene and their relationship via ring-expansion, ring-opening, ring-contraction, and fragmentation

Kvaskoff, David, Bednarek, Pawel and Wentrup, Curt (2010) 2-pyridylnitrene and 3-pyridazylcarbene and their relationship via ring-expansion, ring-opening, ring-contraction, and fragmentation. Journal of Organic Chemistry, 75 5: 1600-1611. doi:10.1021/jo902570d


Author Kvaskoff, David
Bednarek, Pawel
Wentrup, Curt
Title 2-pyridylnitrene and 3-pyridazylcarbene and their relationship via ring-expansion, ring-opening, ring-contraction, and fragmentation
Journal name Journal of Organic Chemistry   Check publisher's open access policy
ISSN 0022-3263
1520-6904
Publication date 2010-03-05
Sub-type Article (original research)
DOI 10.1021/jo902570d
Volume 75
Issue 5
Start page 1600
End page 1611
Total pages 12
Editor C. Dale Poulter
Place of publication Washington, D.C., U.S.A.
Publisher American Chemical Society
Collection year 2011
Language eng
Formatted abstract
(Figure Presented) Photolysis of triazolo[1,5-b]pyridazine 8 isolated in Ar matrix generates diazomethylpyridazines 9Z and 9E and diazopentenynes 11Z and 11E as detected by IR spectroscopy. ESR spectroscopy detected the 3-pydidazylcarbene 10 as well as pent-2-en-3-yn-l-ylidene 12 formed by loss of one and two molecules of N2, respectively. Further photolysis caused rearrangement of the carbenes to 1,2-pentadien-4-yne 13 and 3- ethynylcyclopropene 14. Flash vacuum thermolysis (FVT) of 8 at 400-500 °C with Ar matrix isolation of the products yielded 13, 14, and 1,4-pentadiyne 15. At higher temperatures, glutacononitriles 27Z and 27E were formed as well together with minor amounts of 2- and 3-cyanopyrroles 28 and 29. Tetrazolo[1,5-a]pyridine/2-azidopyridine 22T/22A yields 2-pyridylnitrene 19 as well as the novel open-chain cyanodienylnitrene 23 and the ring-expanded 1,3-diazacyclohepta-l,2,4,6-tetraene 21 on short wavelength photolysis. Nitrenes 19 and 23 were detected by ESR spectroscopy, and cumulene 21 by IR and UV spectroscopy. FVT of 22T/22A also affords 2-pyridylnitrene 19 and diazacycloheptatetraene 21, as well as glutacononitriles 27Z,E and 2- and 3-cyanopyrroles 28 and 29. Photolysis of 21 above 300 nm yields the novel spiroazirene 25, identified by its matrix 1R spectrum. The reaction pathways connecting the four carbenes (10Z,E and 12Z,E) and three nitrenes (19, 23EZ, and 23ZZ) in their open-shell singlet and triplet states are elucidated with the aid of theoretical calculations at DFT, CASSCF, and CASPT2 levels. Three possible mechanisms of ring-contraction in arylnitrenes are identified: (i) via ring-opening to dienylnitrenes, (ii) concerted ring-contraction, and (iii) via spiroazirenes 25, whereby (i) is the energetically most favorable.
© 2010 American Chemical Society.
Keyword Density functional theory
Photochemical interconversion
Photoelectron spectroscopy
Vibrational frequencies
Matrix isolation
Nitrile ylides
ab initio
Rearrangements
Nitrenes
Hetarylnitrenes
Ar-matrix
Carbenes
Q-Index Code C1
Q-Index Status Confirmed Code
Institutional Status UQ

Document type: Journal Article
Sub-type: Article (original research)
Collections: Official 2011 Collection
School of Chemistry and Molecular Biosciences
 
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Created: Sun, 14 Mar 2010, 00:02:53 EST