Given the task definition and input, reply with output. In this task you will be given an answer to a question. You need to generate a question. The answer given should be a correct answer for the generated question.

Some examples of reactions which form carbon -- carbon bonds are aldol reactions, Diels -- Alder reaction, the addition of a Grignard reagent to a carbonyl group, a Heck reaction, a Michael reaction and a Wittig reaction.
list three other organic reactions that can be used to form carboncarbon bonds