The reaction of carbanions with CO is known to form acyl lithiums, but in this case it does not tautomerize to a carbene.When I said the acyl lithium tautomerized to the carbene, I meant the acyl anion resonated to the carbene. Taking the Lithium into account, I must call them tautomers. An alternative pathway is intramolecular Michael addition that would lead to the same enolate, though I prefer the electrocyclization pathway.
I do like the electrocyclization, but the reference I'm consulting claims a pathway with a further intermediate.