Controllable methylenation using renewable ethylene glycol as the methylene source has been developed for the introduction of one or two methylene building blocks in a single reaction. The bridging of enaminones and the synthesis of tetrahydropyrimidines proceeded smoothly with good yields, and bis-enaminones can be further converted into 1,4-dihydropyridines. The presented results shed light on a different usage of ethylene glycol and could inspire novel experimental design by using ethylene glycol as the methylene source.