The value of 2JP-CO as a diagnostic parameter for the structure and thermal reactivity of carbonyl-stabilised phosphonium ylides

TETRAHEDRON

卷:73

Article

Aitken, R. Alan¹  Boubalouta, Youcef¹  Chang, Da¹  Cleghorn, Lee P.¹  Gray, Ian P.¹  Karodia, Nazira^1,2  Reid, Euan J.¹  Slawin, Alexandra M. Z.¹ 

[1] Univ St Andrews, EaStCHEM Sch Chem, St Andrews KY16 9ST, Fife, Scotland

[2] Univ Wolverhampton, Sch Biol Chem & Forens Sci, Wulfruna St, Wolverhampton WV1 1LY, W Midlands, England

关键词: Ylides;    X-ray structure;    NMR coupling constants;    Pyrolysis;    Cycloalkynes;   

DOI  :  10.1016/j.tet.2017.09.016

来源: Elsevier

【 摘 要 】

A survey of 20 carbonyl-stabilised phosphonium ylides with recently reported X-ray structures shows a strong correlation between the C=P to C=O torsion angle and the value of (2)J(P-CO), with high values being associated with an anti configuration and low with syn. Seven new X-ray structural determinations are reported, several for types of ylide not crystallographically characterised before, and these also conform to this pattern. The value of (2)J(P-CO) is then correlated with whether or not thermal extrusion of Ph3PO occurs to give alkynes for over 200 ylides and an empirical rule developed that the extrusion never occurs for ylides where this value is > 11 Hz. This is used to rationalise the anomalous behaviour of some trioxo ylides and cyclic ylides, two of which afford cycloalkynes, isolated after rearrangement as the isomeric 1,3-dienes. The rule also holds for a family of novel highly fluorinated ylides which afford fluorinated alkynes in good yield upon flash vacuum pyrolysis. (C) 2017 Elsevier Ltd. All rights reserved.

【 授权许可】

Free