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Peralkynylated buta-1,2,3-trienes: Exceptionally low rotational barriers of cumulenic C=C bonds in the range of those of peptide C-N bonds

Auffrant, A, Jaun, B, Jarowski, PD, Houk, KN and Diederich, FO (2004) Peralkynylated buta-1,2,3-trienes: Exceptionally low rotational barriers of cumulenic C=C bonds in the range of those of peptide C-N bonds Chem-Eur J, 10, 12. pp. 2906-2911.

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Abstract

A variety of 1,1,4,4-tetraal kynylbutatrienes and 1,4-dialkynylbutatrienes was synthezized by dimerization of the corresponding gem-dibromoolefins. Both H-1 and C-13 NMR spectroscopy indicated that the di- and tetraal-kynylated butatrienes are formed as a mixture of cis and trans isomers. Variable temperature NMR studies evidenced a facile cis-trans isomerization, thus preventing the separation of these isomers by gravity or high-performance liquid chromatography (HPLC). For 1,1,4,4-tetraalkynylbutatrienes, the activation barrier DeltaG(double dagger) was measured by magnetization transfer to be around 20 kcal mol(-1), in the range of the barrier for internal rotation about a peptide bond. Unlike the tetraalkynylated [3]cumulenes, 1,4-dialkynylbutatrienes are more difficult to isomerize and could, in one case, be obtained isomerically pure. Based on experimental data, the rotational barrier DeltaG(double dagger) for 1,4-dialkynylbutatrienes is estimated to be around 25 kcal mol(-1). The hypothesis of a stabilizing effect of the four alkynyl substituents on the proposed but-2-yne-1,4-diyl singlet diradical transition state of this cis-trans isomerization is further supported by a computational study.

Item Type: Article
Authors :
NameEmailORCID
Auffrant, AUNSPECIFIEDUNSPECIFIED
Jaun, BUNSPECIFIEDUNSPECIFIED
Jarowski, PDp.d.jarowski@surrey.ac.ukUNSPECIFIED
Houk, KNUNSPECIFIEDUNSPECIFIED
Diederich, FOUNSPECIFIEDUNSPECIFIED
Date : January 2004
Identification Number : https://doi.org/10.1002/chem.200400218
Related URLs :
Depositing User : Symplectic Elements
Date Deposited : 17 May 2017 11:50
Last Modified : 17 May 2017 11:50
URI: http://epubs.surrey.ac.uk/id/eprint/832921

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