Miura T, * Nakamuro T, Liang C.-J, Murakami M. * Kyoto University, Japan
Synthesis of
trans-Cycloalkenes via Enantioselective Cyclopropanation and Skeletal Rearrangement.
J. Am. Chem. Soc. 2014;
136: 15905-15908
Key words
rhodium - cyclopropanation - [3,3]-sigmatropic rearrangement -
trans-cycloalkenes
Significance
There are few ways to access chiral medium-sized rings possessing a trans double bond (for selected examples, see: A. Deiters et al. Chem. Eur. J.
2002, 8, 1833; X.-N. Wang et al. J. Am. Chem. Soc.
2014, 136, 9802). Such motifs often exhibit planar chirality and may find application in the
synthesis of complex polycyclic frameworks. The authors report an efficient procedure
for the asymmetric synthesis of piperidine-fused trans-cycloalkenes 3 from triazoles 1 and methylenecyclopropenes 2.
Comment
The reaction is initiated by the in situ formation of an α-imino rhodium carbenoid
from triazole 1. Cyclopropanation of the exocyclic methylene group of 2 leads to the formation of spiropentane A, which can then undergo a thermal rearrangement under microwave irradiation to give
trans-cycloalkene 3. The authors propose a concerted mechanism, which draws similarity to the retro-Claisen
[3,3]-sigmatropic rearrangement.
