Henry Rzepa's Blog Chemistry with a twist

September 1, 2018

Organocatalytic cyclopropanation of an enal: (computational) assignment of absolute configurations.

I am exploring the fascinating diverse facets of a recently published laboratory experiment for undergraduate students.[1] Previously I looked at a possible mechanistic route for the reaction between an enal (a conjugated aldehyde-alkene) and benzyl chloride catalysed by base and a chiral amine, followed by the use of NMR coupling constants to assign relative stereochemistries. Here I take a look at some chiroptical techniques which can be used to assign absolute stereochemistries (configurations).



  1. M. Meazza, A. Kowalczuk, S. Watkins, S. Holland, T.A. Logothetis, and R. Rios, "Organocatalytic Cyclopropanation of (E)-Dec-2-enal: Synthesis, Spectral Analysis and Mechanistic Understanding", Journal of Chemical Education, vol. 95, pp. 1832-1839, 2018. http://dx.doi.org/10.1021/acs.jchemed.7b00566

April 4, 2013

Feist’s acid. Stereochemistry galore.

Back in the days (1893) when few compounds were known, new ones could end up being named after the discoverer. Thus Feist is known for the compound bearing his name; the 2,3 carboxylic acid of methylenecyclopropane (1, with Me replaced by CO2H). Compound 1 itself nowadays is used to calibrate chiroptical calculations[1], which is what brought it to my attention. But about four decades ago, and now largely forgotten, both 1 and the dicarboxylic acid were famous for the following rearrangement that gives a mixture of 2 and 3[2]. I thought I might here unpick some of the wonderfully subtle stereochemical analysis that this little molecule became subjected to.



  1. E.D. HedegÄrd, F. Jensen, and J. Kongsted, "Basis Set Recommendations for DFT Calculations of Gas-Phase Optical Rotation at Different Wavelengths", Journal of Chemical Theory and Computation, vol. 8, pp. 4425-4433, 2012. http://dx.doi.org/10.1021/ct300359s
  2. J.J. Gajewski, "Hydrocarbon thermal degenerate rearrangements. IV. Stereochemistry of the methylenecyclopropane self-interconversion. Chiral and achiral intermediates", Journal of the American Chemical Society, vol. 93, pp. 4450-4458, 1971. http://dx.doi.org/10.1021/ja00747a019

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