Wittig reagents carbanion intermediate

It is proposed that this reaction occurs via a mechanism similar to the Wittig Reaction In detail, deprotonation of the Seyferth-Gilbert reagent by potassium -butoxide generates a carbanion, which adds to the carbonyl group to yield an oxaphosphatane then subsequent elimination of dimethylphosphate leads to the formation of a vinyl diazo intermediate from which the vinyl carbene forms by evolution of nitrogen gas final 1,2-migration of the substituent on vinyl carbene yields the alkyne. An illustrative mechanism is displayed here. 

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