I recently came across two contrasting products for the same set of reagents - carboxylic acid and alkyllithium, and wish to understand why exactly any difference exists between the two.
I understand that in steps A, B, and E, the alkylide (hydride in E) is acting as a base and abstracting the acidic proton. I'm fine with that.
However, compare step C and F. Both involve the same reagents (carboxylate and an alkylide). In step C, nucleophilic addition of the ethylide has taken place on the carbonyl group, which is a reasonable step according to me. However, in step F, an ester has been formed instead. I am unable to grasp how an ester can even form in this condition (considering both ethylide and carboxylate are negatively charged), and even if it can form, why wasn't it formed in C as well?
Source: MS Chouhan; Advanced Problems In Organic Chemistry; 11th ed; Q64 and 27 in Alcohol, Ethers and Epoxides