Well, there's 'The Female Man' by Joanna Russ. While not strictly a traditional m2f transformation story in the most basic sense, it does explore gender in a very interesting and complex way that has elements related to the concept. Also, in some science - fiction short stories, like those in certain anthologies, you can find m2f fiction. These often use the idea of advanced technology causing the transformation and then explore how the character adapts in a futuristic society.
One popular m2f fiction work is 'The Danish Girl' which is based on the true story of Lili Elbe, a transgender pioneer. The book and subsequent movie adaptation are quite well - known. Another could be some fan - fictions in the anime or manga world that often play with the m2f transformation concept for their characters.