Heterocumulenes: Reaction of C3O2 with Ketenylidenetriphenylphosphorane; Synthesis and Structure of a Spirobis(cyclobutanedione)

BPh3-Catalyzed [2+3] Cycloaddition of Ph3PCCO with Aldonitrones: Access to 5-Isoxazolidinones with Exocyclic Phosphonium Ylide Moieties

A method for the generation of 5-isoxazolidinones with exocyclic phosphonium ylide functionalities via [2+3] cycloaddition of Ph₃PCCO and aldonitrones has been developed and applied in the synthesis of 4-alkylidene-5-isoxazolidinones via Wittig olefination. The reaction proceeds by BPh₃ catalysis under mild conditions and with a broad substrate scope. A reaction pathway involving the activation of the aldonitrone via interactions with the Lewis acid BPh₃ is proposed.

Trimerisation of carbon suboxide at a di-titanium centre to form a pyrone ring system

Bis(pentalene)dititanium Ti₂(μ:η⁵,η⁵-Pn^†)₂ trimerises carbon suboxide (O Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> C Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> C Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> C Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> O) to form [{Ti₂(μ:η⁵,η⁵-Pn^†)₂}{μ-C₉O₆}], which contains a 4-pyrone core, via the monoadduct [Ti₂(μ:η⁵,η⁵-Pn^†)₂ (η²-C₃O₂)].

The reaction of the syn-bimetallic bis(pentalene)dititanium complex Ti₂(μ:η⁵,η⁵-Pn^†)₂ (Pn^† = C₈H₄(1,4-SiⁱPr₃)₂) 1 with carbon suboxide (O Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> C Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> C Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> C Created by potrace 1.16, written by Peter Selinger 2001-2019 ]]> O, C₃O₂) results in trimerisation of the latter and formation of the structurally characterised complex [{Ti₂(μ:η⁵,η⁵-Pn^†)₂}{μ-C₉O₆}]. The trimeric bridging C₉O₆ unit in the latter contains a 4-pyrone core, a key feature of both the hexamer and octamer of carbon suboxide which are formed in the body from trace amounts of C₃O₂ and are, for example, potent inhibitors of Na⁺/K⁺-ATP-ase. The mechanism of this reaction has been studied in detail by DFT computational studies, which also suggest that the reaction proceeds via the initial formation of a mono-adduct of 1 with C₃O₂. Indeed, the carefully controlled reaction of 1 with C₃O₂ affords [Ti₂(μ:η⁵,η⁵-Pn^†)₂ (η²-C₃O₂)], as the first structurally authenticated complex of carbon suboxide.

Activation of carbon suboxide (C3O2) by U(iii) to form a cyclobutane-1,3-dione ring

[U(η⁵-C₅H₄SiMe₃)₃] reductively couples three C₃O₂ molecules to form a tetranuclear complex with a central cyclobutane-1,3-dione ring, via an intermediate bridging ketene complex.