Abstractsym‐Trinitrobenzene reacts successively with three molecules of diazomethane yielding “trismethylene‐trinitrobenzene” (VIII). In each stage an intermediate diazonium betaine (II, V and VII) is postulated with considerable negative charge delocalisation. Such betaines lose nitrogen to give cyclopropanes rather than retaining nitrogen with ring closure to give pyrazolines. Pyrazoline formation becomes important when charge delocalisation is restricted, as in the reaction of the non‐conjugated double bond in VIII with a (fourth) molecule of diazomethane yielding the stable pyrazoline IX either via a betaine or by 1,3‐dipolar addition.