New evidence on the structure of the product from the reaction of cyclic 2,4,6-trialkylphenylphosphine oxides with dimethyl acetylenedicarboxylate (DMAD); formed by an inverse Wittig reaction type protocol
New evidence based on spectroscopy, quantum chemical calculations and reactivity suggest that the spirocyclic oxaphosphetes (5) formed by the [2+2] cycloaddition of the title P-heterocycles (4) and DMAD are intermediates to afford a stabilised phosphonium ylide (6) existing as two conformers (6A and B).