Is this electrical related or plumbing? Which one will dictate where to go for the parts, it's unwise to use plumbing parts for electrical, but reducing bushings are avail. for either.
personally I would use a box or conduit body to transition -seems like the conductors would be shredded when entering the 1" hole on a 4" reducer unless it was a bell type. Maybe stack two bell types, one from 4-2,1/2 and one 2,1/2 to 1"