Sound, he was invited to become music director of the Seattle Symphony, which he conducted from 1948–1951 while undertaking guest engagements in San Francisco and Buenos Aires. He then went to Algiers to conduct there and in Tunis during the winter of 1952-53. He was music director of the Orchestre Symphonique de Liège from 1964-1967, and professor of conducting at the Paris Conservatoire from 1962 to 1974, where he established a more demanding schedule for his students, who included Yan Pascal Tortelier, Eliahu Inbal, Jacques Mercier, Marc Soustrot and Jean-Claude Casadesus. He conducted some of the first modern performances of Jean-Philippe Rameau's Zoroastre, at the Grand Théâtre de Bordeaux and the Opéra-Comique in 1964. The BBC in Manchester invited him to conduct an opera of his choice in 1973, which turned out to be Emmanuel Chabrier's Le roi malgré lui, for which he chose a French cast. In February 1981, Rosenthal made his debut at the Metropolitan Opera New York in a mixed-bill of 20th century French stage works, returning in 1983 for Francis Poulenc's 1957 operatic masterpiece Dialogues des carmélites and for further appearances in 1986-87. He returned to Seattle in 1986 to conduct Richard Wagner's Ring cycle at the Seattle Opera. He conducted the first performance of Claude Debussy's radical 1902 operatic masterpiece Pelléas et Mélisande in Russia, in Moscow in 1988, and later that year premiered the same work in Caracas, Venezuela. In 1992, he conducted a production of Padmâvatî by Albert Roussel at the Opera Bastille. Composer Rosenthal composed prolifically in many classical genres, including operas, operettas, ballets, 13 works for orchestra, choral works both with orchestra and a cappella, works for solo voice and orchestra, chamber music, and music for voice and piano as well as for solo piano. The wide variety of his work, in terms of both genre and tone, reflects his refusal to accept the stylistic compartmentalization prevalent in Paris in the 1920s. His reputation as a composer was sealed in France with Jeanne d'Arc, first performed in 1936, although this was followed by a production of the light-hearted one-act operetta La Poule Noire of 1937. His best-known compositional work was not his own, the 1938 ballet Gaîté Parisienne orchestrated from operetta selections by Jacques Offenbach (copied manually by assistants who chose them from piano scores they speed-read in the Harvard University music library, the most complete repository of Offenbach scores known