This article is from the FAQ, by with numerous contributions by others.
You may NOT file an I-130 (Petition for Alien Relative) for
E. A husband or wife if you gained lawful permanent resident status
by virtue of a prior marriage to a United States citizen or lawful
permanent resident unless:
1) a period of five years has elapsed since you became a lawful
permanent resident; OR
2) you can establish by clear and convincing evidence that the
prior marriage (through which you gained your immigrant status)
was not entered into for the purpose of evading any provision of
the immigration laws; OR
3) your prior marriage (through which you gained your immigrant
status) was terminated by the death of your former spouse.