The actual number of C−C bond forming reactions is very low. Grignards may be made fairly easily from hydrocarbyl halides and magnesium turnings, and usually react quantitatively with carbonyls species to make a C−C bond. The C−C bond is moreover functionalized with an hydroxyl group after workup.
The best way to make a carboxylic acid is to pour the Grignard onto dry ice (and step back):
R−MgX+CO2(s)→RC(=O)OMgX
Here the alkyl (hydrocarbyl) chain has been extended by 1. If an epoxide, i.e. ethylene oxide, a cyclic ether, is used the carbon chain is extended by 2. Of course, some precautions have to be taken with the reaction; namely the exclusion of water and protic solvents.
