Methods of synthesizing intermediates useful for the synthesis of halichondrin B analogs are described.

Methods of synthesizing intermediates useful for the synthesis of halichondrin B analogs are described.

Methods of synthesizing intermediates useful for the synthesis of halichondrin B analogs are described.

Methods of synthesizing intermediates useful for the synthesis of halichondrin B analogs are described.

Methods of synthesizing intermediates useful for the synthesis of halichondrin B analogs are described.

Disclosed is a process for preparing dihydro-2H-pyran derivatives of formula I: ##STR00001## wherein R.sup.1 and R.sup.2 are defined herein. The process of the invention provides the compound of formula I in concise cascade reactions and in one pot. The compound of formulae I prepared by the process of the invention and its further transformed derivatives are useful for making pharmaceutical composition for the treatment of proliferative diseases.

Methods of synthesizing intermediates useful for the synthesis of halichondrin B analogs are described.