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Oxygen‐Initiated Stereoselective Thermal Isomerisation of a Cyclobutane Derivative in the Solid State
Author(s) -
Chanthapally Anjana,
Yang Hui,
Quah Hong Sheng,
Webster Richard D.,
Schreyer Martin K.,
Wong Ming Wah,
Vittal Jagadese J.
Publication year - 2014
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.201405228
Subject(s) - isomerization , cyclobutane , chemistry , cycloaddition , stereoselectivity , photochemistry , oxygen , cis–trans isomerism , computational chemistry , stereochemistry , organic chemistry , catalysis , ring (chemistry)
Solid‐state [2+2] photochemical cycloaddition reactions have been extensively studied after the classical work of Schmidt in the 1960s. Of these, trans ‐1,2‐bis(4′‐pyridyl)ethylene (bpe) is one of the well‐studied alkenes to synthesize tetrakis(4‐pyridyl)cyclobutane (tpcb). However, almost all the solid‐state [2+2] cycloaddition reactions of bpe yielded, almost exclusively, one of the four possible isomers, namely, the rctt ‐tpcb ( r=regio c= cis and t=trans ). Here we describe a stereoselective synthesis of the tetrahedrally disposed rtct ‐tpcb by the solid‐state thermal isomerization of the rctt ‐isomer in atmospheric air. We propose that this isomerization occurs through a topochemical unimolecular mechanism by a radical chain pathway, initiated by molecular oxygen. This is supported by the nature of products formed in air and nitrogen, detection of a radical in ESR spectral studies, ESI‐MS crossover experiments, VT PXRD studies along with QM, MD and docking calculations. The formation of a unique isomer by thermal isomerization may be a general phenomenon to quantitatively synthesize other useful stereoisomers from the existing isomers of cyclobutane derivatives.