Synthesis of the C17–C23 subunit of Ionomycin from C1-functionalized 8-oxabicyclo[3.2.1]oct-6-en-3-one. New synthetic methodology to prepare polyfunctionalized heptane building blocks with four stereocenters

Abstract The application of a new methodology to synthesize the C17–C23 subunit of Ionomycin is presented. This synthetic methodology is based on the preparation of heptane building blocks with four stereocenters and up to four different organic functionalities. 2,4-Dimethyl-1-methoxy-8-oxabicyclo[3.2.1]oct-6-en-3-one has been used as a key intermediate, which can easily be prepared by a [4+3] cycloaddition reaction between 2-methoxy-furan and the oxyallyl cation generated in situ from 2,4-dibromo-3-pentanone. This cycloadduct has an acetal functionality on C1 which allows the easy opening of the oxabicyclic system, affording versatile synthons.