Complex sentence: To this end, he enrolled in the Juilliard School of Music, which he attended for three years, but when he was offered work at CBS as an arranger for bandleader Fred Waring, he dropped out of Juilliard to accept it.
Split into simpler sentences: To this end, he enrolled in the Juilliard School of Music, which he attended for three years. But when he was offered work at CBS as an arranger for bandleader Fred Waring, he dropped out of Juilliard to accept it.