Sydnone Photochemistry: Direct Observation of Earl’s Bicyclic Lactone Valence Isomers (Oxadiazabicyclo[2.1.0]pentanones), Formation of Carbodiimides, Reaction Mechanism, and Photochromism

Rakesh N. Veedu; David Kvaskoff; Curt Wentrup

doi:10.1071/CH13536

RESEARCH ARTICLE

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Sydnone Photochemistry: Direct Observation of Earl’s Bicyclic Lactone Valence Isomers (Oxadiazabicyclo[2.1.0]pentanones), Formation of Carbodiimides, Reaction Mechanism, and Photochromism

Rakesh N. Veedu ^A , David Kvaskoff ^A and Curt Wentrup ^A ^B

+ Author Affiliations

- Author Affiliations

^A School of Chemistry and Molecular Biosciences, The University of Queensland, Brisbane, Qld 4072, Australia.

^B Corresponding author. Email: wentrup@uq.edu.au

Australian Journal of Chemistry 67(3) 457-468 https://doi.org/10.1071/CH13536
Submitted: 7 October 2013 Accepted: 31 October 2013 Published: 27 November 2013

Abstract

The matrix photolyses of 3-phenyl-, 3-pyridyl, and 3,4-diphenylsydnones 16, 19, and 22 were investigated by matrix-isolation infrared spectroscopy. The formation of the neutral, bicyclic lactone valence isomers postulated by Earl – the oxadiazabicyclo[2.1.0]pentanones exo-17 and exo-20 – was clearly observed in the first two cases and is also likely in the case of exo-23 (C=O absorptions in the IR at 1881, 1886, and 1874 cm^–1, respectively). The efficient photodecomposition of sydnones to carbodiimides RN=C=NR′ (18, 21, and 24) and CO₂ was established in all three cases. The formation of benzonitrile 27 and azacycloheptatetraene 29 in the matrix photolysis of diphenylsydnone 22 is indicative of diphenylnitrile imine PhCNNPh 26 as an intermediate (2340 cm^–1). Neither bicyclic lactones nor carbodiimides have been observed previously in sydnone photochemistry. A general reaction mechanism for the formation of carbodiimides, nitrile imines, and photochromism is put forward.

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Sydnone Photochemistry: Direct Observation of Earl’s Bicyclic Lactone Valence Isomers (Oxadiazabicyclo[2.1.0]pentanones), Formation of Carbodiimides, Reaction Mechanism, and Photochromism

Abstract

References

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