Ring Opening of Vinylcyclopropane Radical Cations via Stereoselective Sigmatropic Shifts

Hengxin Weng, Qasim Sheik, Heinz D. Roth

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43 Scopus citations


The electron transfer photoreaction of (1R,5R)-(+)-sabinene (4-methylene-1-(1-methylethyl)bicyclo[3.1.0]-hexane; 1) with 1,4-dicyanobenzene and phenanthrene gives rise to (S)-(+)-β-phellandrene (3-methylene-6-(1-methylethyl)cyclohexene; 3), whereas (1S,5S)-(+)-α-thujene (2-methyl-5-(1-methylethyl)bicyclo[3.1.0]hex-2-ene; 2) is converted to (S)-(+)-α-phellandrene (2-methyl-5-(1-methylethyl)-1,3-cyclohexadiene; 7). Both products can be rationalized via stereoselective sigmatropic shifts in the corresponding radical cations. For 1•+, a [1,3] sigmatropic shift transfers a hydrogen from C6 to C1with inversion of stereochemistry at Ci. For 2+, experiments with 2-3-d1 indicate that a [1,3] sigmatropic shift (from C6 to C1) competes with a homo-[1,5] sigmatropic shift (from C2 to C1); the latter migration is slightly favored. The stereochemical relationship between the chiral educts, 1 and 2, and the ring-opened products, 3 and 7, requires that the radical cations, 1•+ and 2•+, retain the chirality of their precursors; they cannot be ring-opened. The rearrangement of 2•+ takes a significantly different course from the thermal isomerization of its parent, 2, which proceeds via the vinylcyclopropane rearrangement. The stereochemical course established for the rearrangement of 2•+ is the first case of competing sigmatropic shifts in radical cations.

Original languageEnglish (US)
Pages (from-to)10655-10661
Number of pages7
JournalJournal of the American Chemical Society
Issue number43
StatePublished - 1995

All Science Journal Classification (ASJC) codes

  • Catalysis
  • Chemistry(all)
  • Biochemistry
  • Colloid and Surface Chemistry


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