Abstract
The authors are grateful to EPSRC and Glaxo-Wellcome (now GSK) for their support of this work through a CASE Studentship to TM.
Highlights
We recently introduced the value of the two-bond NMR coupling constant 2JP–CO as a diagnostic parameter for the reactivity of β-oxophosphonium ylides 1 towards thermal extrusion of Ph3PO to give alkynes (Scheme 1).[1]
All known ylides that do undergo such extrusion to form an alkyne have 2JP–CO < 11 Hz, while those with values above this do not. The latter group includes formyl and alkoxycarbonyl ylides (R2 = H, O-Alkyl) where the failure of extrusion as well as the high J value is associated with the C=P and C=O functions being aligned anti rather than syn to one another
flash vacuum pyrolysis (FVP) of both 4 and 5 gave disappointing results, with the only products obtained in the cold trap being a trace of Ph3PO in the first case and a mixture of Ph3PO, Ph3PS, Ph3P and triphenylphosphoranylideneketene 11 in the second
Summary
We recently introduced the value of the two-bond NMR coupling constant 2JP–CO as a diagnostic parameter for the reactivity of β-oxophosphonium ylides 1 towards thermal extrusion of Ph3PO to give alkynes (Scheme 1).[1] All known ylides that do undergo such extrusion to form an alkyne have 2JP–CO < 11 Hz, while those with values above this do not The latter group includes formyl and alkoxycarbonyl ylides (R2 = H, O-Alkyl) where the failure of extrusion as well as the high J value is associated with the C=P and C=O functions being aligned anti rather than syn to one another. A wide range of heterocyclic phosphonium ylides are known,[2,3] and among those with published 2JP–CO values, our attention was drawn to ylide 4 and its thio-analogue 5 These are readily prepared from dichloromaleic (thio)anhydride and, with 2JP–CO values for the ketone carbonyl of 8 Hz4 and 7 Hz5 respectively, seemed possible precursors for thermal generation of dehydromaleic anhydride and its thio analogue. Such heterocyclic alkynes are elusive and highly reactive compounds that have attracted considerable interest,[6] and we describe here for the first time the thermal decomposition of 4 and 5
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
