A Direct Entry to Bicyclic Cyclobutenes via Platinum-Catalyzed ­Cycloisomerization of Allenynes

Abstract

Allenynes underwent cycloisomerization in the presence of a catalytic amount of platinum(II) chloride at 80 °C to give ­bicyclic cyclobutenes. A mechanism involving non-classical ­carbocationic intermediates was proposed for the formation of ­cyclobutenes.

Key words

alkynes - allenes - cyclobutenes - cyclizations - platinum

References and Notes

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7

CO accelerates the PtCl₂-catalyzed cycloisomerization of enynes (ref. 3a). However, no accelerating effect of CO was observed in the present allenyne cycloisomerization.

8

Other PtCl₂ complexes bearing additional ligands, such as PtCl₂(cod) and PtCl₂(PPh₃)₂, failed to exhibit any catalytic activity.

9

This abstraction process (B → F) could proceed either inter- or intramolecularly.