Understanding anionic Chugaev elimination in pericyclic tetracene formation

Burroughs, Laurence; Ritchie, John; Woodward, Simon

Abstract

The reaction pathway for the formation of tetracenes from the diols 1,2-C6H4(CHOHC≡CAr)2 , LiHDMS, CS2 and MeI has been modelled by computational methods at the CBS-QB3 level of theory. Comparison of PhCHOC(=S)YCCPh (Y = S- or SMe) indicates a slight kinetic advantage for the anionic system towards [3,3]-sigmatropic rearrangement [Eact(calc.) 19.7 vs 21.8 kcal mol-1]. Using anthracene-based models, 10-{SC(=O)Y}-4a,10-dihydroanthracene (Y = S- or SMe), allows direct comparison of both syn and anti-manifolds in the neutral vs. anionic Chugaev elimination. Syn elimination of [HSC(=O)S]- is distinctly favoured [Eact(calc.) 11.4 kcal mol-1] vs. syn elimination of neutral methylated HSC(=O)SMe [Eact(calc.) 27.5 kcal mol-1]. The smaller barrier to syn elimination of the anionic leaving group is in accord with the low temperature conditions required for this Chugaev reaction (60 oC) and suggests a general advantage in carrying out Chugaev eliminations in anionic manifolds.

Citation

Burroughs, L., Ritchie, J., & Woodward, S. (2016). Understanding anionic Chugaev elimination in pericyclic tetracene formation. Tetrahedron, 72(13), https://doi.org/10.1016/j.tet.2016.02.025

• Journal Article Type: Article
• Acceptance Date: Feb 8, 2016
• Online Publication Date: Feb 10, 2016
• Publication Date: Mar 31, 2016
• Deposit Date: Feb 10, 2016
• Publicly Available Date: Feb 10, 2016
• Journal: Tetrahedron
• Print ISSN: 0040-4020
• Electronic ISSN: 0040-4020
• Publisher: Elsevier
• Peer Reviewed: Peer Reviewed
• Volume: 72
• Issue: 13
• DOI: https://doi.org/10.1016/j.tet.2016.02.025
• Public URL: https://nottingham-repository.worktribe.com/output/778269
• Publisher URL: http://www.sciencedirect.com/science/article/pii/S0040402016300886
• Contract Date: Feb 10, 2016