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

A survey of 20 carbonyl-stabilised phosphonium ylides with recently reported X-ray structures shows a strong correlation between the CP to CO torsion angle and the value of 2JP–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 2JP–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.EPSRC (U.K.) for a DTA Studentship (Grant No. EP/P505712/1

Recent Advances in the Synthesis of Heterocyclic Compounds Using Flash Vacuum Pyrolysis

Applications of flash vacuum pyrolysis to the synthesis of heterocyclic compounds published between 2000 and 2015 are described in six major sections with 150 literature references. The emphasis is on methods suitable for preparation of stable heterocyclic products in multi-gram quantities. Consideration of the relatively few reports of synthesis of three- and four-membered rings is followed by the largest single section on synthesis of five-membered rings, mainly those containing one or two nitrogen atoms. A further major section considers synthesis of six-membered ring products, again predominantly containing nitrogen, before final shorter sections on seven-membered, eight-membered and larger rings