The present invention provides methods for the synthesis of ketones involving a Ni/Zr-mediated coupling reaction. The Ni/Zr-mediated ketolization reactions can be used in the synthesis of halichondrins (e.g., halichondrin A, B, C; homohalichondrin A, B, C; norhalichondrin A, B, C), and analogs thereof. Therefore, the present invention also provides synthetic methods useful for the synthesis of halichondrins, and analogs thereof. Also provided herein are compounds (i.e., intermediates) useful in the synthesis of halichondrins, and analogs thereof. In particular, the present invention provides methods and compounds useful in the synthesis of compound of Formula (H3-A).