I tried to book LAX-EZE on LA but could only do so in D class. So I opted for A class LAX-SCL and another segment in D class on the same plane. Since there is no first class LAX-EZE and the segment is LAX-EZE, you could only book into D for the entire flight. And therein lies the problem, no guarantee of flying and getting first class service and miles. I suggest that you book the SCL-LAX in first and buy a separate flight EZE-LAX.