Some English teachers claim that “interested to” is always wrong, but this claim is not substantiated by actual usage. The fact is, the forms “interested in” and “interested to” mean different things and are common even in very formal writing.
“Interested in” is used when referring to a thing you are attracted to or that you would like to do, for example:
This sentence means that you are attracted to English literature; you find it interesting and would like to know more about it.
On the other hand, “interested to” may be used when you want to obtain more information about a fact, as in
“Interested to” can be used only with verbs of perception and “knowing”, such as:
When used in the past tense, the expression means “I found out about it and the information was interesting”, e.g.
which should be understood as
In practice, “interested in doing” is much more common than “interested to do”, simply because people usually want to express interest in an activity, as in
When “interested” is used with a verb that is not a verb of perception, “in doing” is the only correct form. When the verb in question is a verb of perception, you should ask yourself, “Is it possible to replace ‘be interested to/in do(ing)’ with ‘want to find out’?” If the answer is yes, it is fine to use “interested to”; if it is no, you should always use “interested in”. For example,
is possible because the intended meaning is “I want to find out why she committed the crime.” Note, however, that many native speakers use “interested to know” and “interested in knowing” in the sense of obtaining information interchangeably and could as well say
while others find the second variant less natural and would only use “in knowing” when “know” is used in the sense of “have knowledge of”, as in
In this case, most native speakers would consider “interested to know” less natural.