Methods for the synthesis of carbon-13 labelled acids and esters

Syntheses of isotopically labelled putative biosynthetic intermediates to the natural products monocerin 1, hectochlorin 2 and strobilurin A 3 are described. For the preparation of [9,10‐13C2]dihydroisocoumarin 10, a stereoselective aldol condensation of 13C2‐acetylated chiral auxiliary 5 was used to assemble the labelled C9‐C14 fragment. The preferred approaches to the syntheses of [1,2‐13C2]5,5‐dichlorohexanoic acid 15 and the N‐acetylcysteamine derivative of [1,2‐13C2]cinnamic acid 19 involved a Horner‐Wadsworth‐Emmons chain extension and Knoevenagel reaction, respectively. Copyright © 2007 John Wiley & Sons, Ltd.