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Naphthalene Isotopomers from Isotope‐Labelled Phenyl‐Annelated 1,3‐Hexadien‐5‐ynes Facilitate an Evaluation of Competing Radical Cycloisomerization Pathways
Author(s) -
Schulz Kathrin,
Hofmann Jörg,
Findeisen Matthias,
Zimmermann Gerhard
Publication year - 1998
Publication title -
european journal of organic chemistry
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.825
H-Index - 155
eISSN - 1099-0690
pISSN - 1434-193X
DOI - 10.1002/(sici)1099-0690(199810)1998:10<2135::aid-ejoc2135>3.0.co;2-3
Subject(s) - chemistry , cycloisomerization , isotopomers , radical , naphthalene , photochemistry , medicinal chemistry , toluene , carbene , reaction intermediate , catalysis , organic chemistry , molecule
The thermal cycloisomerization of the isotope‐labelled 1‐phenyl‐1‐buten‐3‐ynes 1 {including the [3‐ 13 C,4‐D]1‐phenyl‐1‐buten‐3‐yne ( 6 ) and the [4‐D]1‐phenyl‐1‐buten‐3‐yne ( 9 ) formed as intermediates} has been studied. The investigations were performed in a quartz flow system at a temperature of 650 °C ( 1 , 6 ) [and over the range 625‐750 °C for ( 9 )] at a reaction time of 0.3 s in the presence of different diluent gases (H 2 , N 2 , N 2 ‐toluene). Spectroscopic analyses of the naphthalene isotopomers formed allow the evaluation of competing radical reaction channels in addition to reactions occuring by electrocyclic and carbene‐like ring closure. [1] A mechanistic analysis for the conversion of 1 undoubtedly suggests a predominant reaction course via phenyl‐type radical intermediates ( 1c / 6c ), followed by their exocyclization to the indenylcarbenyl radicals 1f / 6f and the homoallyl‐like rearrangement of the latter to the 1,2‐dihydronaphthyl radicals 1i / 6i at 650 °C. With increasing temperature, other competing reactions (endocyclizations of vinyl‐ and phenyl‐type radicals as well as neophyl‐like rearrangements of the indenylcarbinyl radicals 1f / 6f ) gain in importance.