PtCl 2 -Catalyzed Rearrangement of Methylenecyclopropanes

  • 10.1021/ja061392y
  • Journal of the American Chemical Society
  • p 6306-6307, Volume 128, Issue 19,
  • journal-article
Alkylidenecyclopropanes readily convert into cyclobutene derivatives on treatment with catalytic amounts of PtCl 2 . The reaction is strongly accelerated when performed under an atmosphere of CO (1 atm). The resulting cyclobutenes are isolated in good to excellent yields for substrates bearing aliphatic as well as aromatic substituents R on their olefinic site. If the substituent R, however, is a very electron-rich arene, the cyclobutenes initially formed react further to give dimeric products with a previously unknown 1,2,2a,7a-tetrahydrospiro[cyclobuta[a]indene-7,1‘-cyclobutane skeleton. A mechanism accounting for these experimental observations as well as for a deuterium-labeling experiment is proposed which implies reactive intermediates at the nonclassical cation/carbene interface. Furthermore it is shown that the PtCl 2 -catalyzed cyclobutene formation can be geared with subsequent ring-opening/ring-closing metathesis (ROM/RCM) events. Finally, a convenient “one pot” method for the preparation of the alkylidenecyclopropane substrates used in this study is presented, which is based on a modified Julia−Kocienski olefination of aldehydes with readily available 1-tert-butyl-1H-tetrazol-5-yl-cyclopropyl sulfone under Barbier conditions.

Review

Good for Aldehydes, Modification for Ketone Substrates

This communication by Furstner and co-worker reported a novel rearrangement of methylenecyclopropanes 3 for the construction of variously substituted cyclobutenes and derivatives.

I am particularly interested in the preparation of cyclopropylidene bearing substrates 3. In...

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