Complex sentence: At the time, "Secret" was experiencing success on the US record charts, to keep the song current in dance clubs, Madonna requested remixes of the song from Junior Vasquez, who was a DJ at the Sound Factory nightclub in New York.
Split into simpler sentences: At the time, "Secret" was experiencing success on American charts. To keep the song current in dance clubs, Madonna requested remixes of the song for Junior Vasquez, who was a DJ at the Sound Factory nightclub in New York.