[noun] + に至って [noun] + に至り [verb (dictionary form)] + に至って [verb (dictionary form)] + に至り
に至って means "only when things reached (this point)": a situation got worse and worse, and only at that stage did something happen. It follows a noun, or a verb in the dictionary form, and the second half usually carries ようやく, やっと or はじめて初めて, because the reaction came late.
A verb before に至って stays in the dictionary form, even in a past sentence: ×倒れたに至って.
The two differ by one particle and mean different things. に至って is about time: "only once it came to that". にいたっては至っては picks out the worst case in a group: "and as for X…".
に至って is written Japanese. In conversation, "only when" is てはじめて or になってやっと.