Oxaphospholes and bisphospholes from phosphinophosphonates and α,β-unsaturated ketones

Anna I. Arkhypchuk, Andreas Orthaber, Viorica Alina Mihali, Andreas Ehlers, Koop Lammertsma, Sascha Ott

Research output: Contribution to journalArticlepeer-review

21 Citations (Scopus)

Abstract

The reaction of a {W(CO)5}-stabilized phosphinophosphonate 1, (CO)5WPH(Ph)-P(O)(OEt)2, with ethynyl- (2 a-f) and diethynylketones (7-11, 18, and 19) in the presence of lithium diisopropylamide (LDA) is examined. Lithiated 1 undergoes nucleophilic attack in the Michael position of the acetylenic ketones, as long as this position is not sterically encumbered by bulky (iPr)3Si substituents. Reaction of all other monoacetylenic ketones with lithiated 1 results in the formation of 2,5-dihydro-1,2-oxaphospholes 3 and 4. When diacetylenic ketones are employed in the reaction, two very different product types can be isolated. If at least one (Me)3Si or (Et)3Si acetylene terminus is present, as in 7, 8, and 19, an anionic oxaphosphole intermediate can react further with a second equivalent of ketone to give cumulene-decorated oxaphospholes 14, 15, 24, and 25. Diacetylenic ketones 10 and 11, with two aromatic acetylene substituents, react with lithitated 1 to form exclusively ethenyl-bridged bisphospholes 16 and 17. Mechanisms that rationalize the formation of all heterocycles are presented and are supported by DFT calculations. Computational studies suggest that thermodynamic, as well as kinetic, considerations dictate the observed reactivity. The calculated reaction pathways reveal a number of almost isoenergetic intermediates that follow after ring opening of the initially formed oxadiphosphetane. Bisphosphole formation through a carbene intermediate G is greatly favored in the presence of phenyl substituents, whereas the formation of cumulene-decorated oxaphospholes is more exothermic for the trimethylsilyl-containing substrates. The pathway to the latter compounds contains a 1,3-shift of the group that stems from the acetylene terminus of the ketone substrates. For silyl substituents, the 1,3-shift proceeds along a smooth potential energy surface through a transition state that is characterized by a pentacoordinated silicon center. In contrast, a high-lying transition state TS(E'-F')R=Ph of 37 kcal mol-1 is found when the substituent is a phenyl group, thus e

Original languageEnglish
Pages (from-to)13692-13704
Number of pages13
JournalChemistry - A European Journal
Volume19
Issue number41
DOIs
Publication statusPublished - 4 Oct 2013
Externally publishedYes

Keywords

  • cumulenes
  • density functional calculations
  • domino reactions
  • phosphaorganic chemistry
  • reaction mechanisms

ASJC Scopus subject areas

  • Catalysis
  • Organic Chemistry

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