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DOI: 10.1055/s-0034-1379684
Synthesis of trans-Cycloalkenes via Cyclopropanation and Rearrangement
Publication History
Publication Date:
15 December 2014 (online)

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.
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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.
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