Synthesis, structure and pyrolysis of stabilised phosphonium ylides containing saturated oxygen heterocycles

Abstract

A range of twelve stabilised phosphonium ylides containing tetrahydrofuran, tetrahydropyran or 2,2-dimethyl-1,3-dioxolane rings have been prepared and fully characterised, including one X-ray structure determination of each type. The X-ray structures confirm the PvC and CvO functions to be syn and all the compounds undergo thermal extrusion of Ph 3 PO to give the corresponding alkynes. In some cases there is also competing loss of Ph 3 P to give different carbene-derived products and evidence has been obtained for the generation of 2-phenyloxete in this way. Raising the pyrolysis temperature leads in several cases to new secondary reactions of the alkyne products involving a sequence of alkyne to vinylidene isomerisation, intramolecular CH insertion, and retro Diels Alder reaction.

Natural Products Containing the Oxetane and Related Moieties Present Additional Challenges for Structure Elucidation: A DU8+ Computational Case Study

“…Considerable challenges appear to complicate structure elucidation of the unsaturated oxetane relatives, oxetes. Oxetes are known and isolable, although very few of them have been fully characterized with 13 C NMR Figure A shows the examples of three small organic molecules containing the oxete moiety for which 13 C data is available.…”

A tribute to Professor Aitken

“…Using this method products prepared in good yield have included acetylenic esters 3 and terminal alkynes 4, 3 diacetylenic esters 5 and terminal diynes 6, 4 diacyl alkynes 7, 5 conjugated enynes 8, 6 unsymmetrical 1,3-diynes 9, 7 trioxo alkynes 10, 8 trisubstituted naphthalenes such as 11, 9 extended dialkynes such as 12 and 13, 10 alkynyl ketones 14 and alkoxycarbonyl dienes 15, 11 and oxygen heterocycle-containing alkynes such as 16-18. 12…”