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

Gas-phase domino cyclization of phosphonium ylides leading to the total synthesis of Eustifoline D

“…Once this data was obtained however, the highly consistent pattern of 31 P coupling provided good confirmation of the structures, and the low value of 6 Hz for 2 J P-CO meant that the Ph 3 PO elimination was likely to be successful. 24,25 When ylides 12a-d were subjected to FVP, the desired elimination of Ph 3 PO readily occurred but the pattern of heterocyclic products obtained was more complex than expected. At the low temperature of 500 °C, FVP of furyl compound 12c gave a moderate yield of enyne 13, thus confirming the occurrence of the desired initial step.…”

Flash vacuum pyrolysis of oxo-stabilised phosphonium ylides containing methoxythiophene and methylthiophene groups

“…In order to elucidate the unexpected pyrolysis behaviour, the deuterium-labelled salt 32 was similarly used to generate the labelled ylide 36. All three ylides were formed in excellent yield as stable solids and the 2 J P-CO values of 5-6 Hz again suggested successful thermal extrusion of Ph 3 PO [28].…”

“…The ylides 8-13 were obtained as high-melting crystalline solids which were stable on storage and showed the expected spectroscopic properties including 31 extending throughout the P-phenyl groups, the oxo ylide function and to at least the first carbon of both Ph/Et and thienyl groups. Importantly for the planned extrusion of Ph 3 PO under FVP conditions, the value of the phosphorus coupling to the carbonyl group, 2 J p-CO was 6-8 Hz, meaning that the extrusion should proceed readily since we recently showed [28] an empirical correlation with a cut off of 10 Hz. The expected process upon FVP of ylides 8 and 9 (Scheme 4) involves cyclisation of the alkyne-containing thienyloxy radical to give the thieno[3,2-b]furyl radical which then gives an isolable product in which the substituent may be the same or different.…”

“…cinnamoyl chloride. The three ylides 25, 26 and 29 were obtained as high-melting stable crystalline solids with values of 2 J P-CO of 8-9 Hz leading us to predict [28] Unfortunately, however no useful products were obtained from FVP of any of the three ylides. In each case there was extensive decomposition in the range 700-750 °C with no identifiable heterocyclic products obtained.…”

New reactions and reactive intermediates in the pyrolysis of cyclic phosphonium ylides

“…1 All known ylides that do undergo such extrusion to form an alkyne have 2 J P-CO < 11 Hz, while those with values above this do not. The latter group includes formyl and alkoxycarbonyl ylides (R 2 = 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.…”