cheminform abstract: organophosphorus compounds. part 137. the unusual dienophilicity...
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1999 organo-phosphorus compounds, nonmetal heterocycles
organo-phosphorus compounds, nonmetal heterocyclesS 0087
23 - 200Organophosphorus Compounds. Part 137. The Unusual Dienophilic-ity Trimethylsilylphosphaacetylene. Reaction of title compound (I)with butadienes (II) gives tricyclic compounds (III). Ab initio MO calculationsfurnish proof of the postulated intermediates of a reaction sequence, consistingof DielsAlder reaction, phospha-ene reaction and intramolecular [4 + 2]cycloaddition. The molecular structures of (III) and their metal carbonylcomplexes are determined by NMR and mass spectroscopy. Reaction of (I)with cyclohexadiene needs a long reaction time to get completed and gives theisolated product (V) in low yield because a large amount of the short-livedphosphaacetylene (I) is lost in oligo- and polymerization processes. Again, nointermediates of phospha-ene reaction and subsequent intramolecular [4 + 2]cycloaddition are detected, what is explained by ab initio calculations. Reactionof (I) with cyclopentadiene is achieved in a three-step sequence of [4 + 2]cycloaddition, homo-DielsAlder reaction, and homo[4 + 1] cycloadditionand yields surprisingly spiro compound (VII). (FIEDLER, WOLFGANG;LOEBER, OLIVER; BERGSTRAESSER, UWE; REGITZ, MANFRED; Eur.J. Org. Chem. (1999) 2, 363-371; Fachbereich Chem., Univ. Kaiserslautern,D-67663 Kaiserslautern, Germany; EN)