The vinylation of 4a with 1a-D2 resulted in a 1:1 mixture of 5a-D isomers and no di-deuterated products were observed (Scheme 5b). A crossover experiment was performed with 1a-D2 and 1d, in which the expected products 5a-D and 5c were formed together with a trace amount of 5c-D (Scheme 5c). Finally, deuterated phosphine oxide 4a-D was employed with VBX 1a, which resulted in the expected product 5a as major product, with some deuterium incorporation to 5a-D, now with the (E)-isomer as major isomer (Scheme 5d).