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- 13 C 2 ]dihydroisocoumarin 10, a stereoselective aldol condensation of 13 C 2 -acetylated chiral auxiliary 5 was used to assemble the labelled C9-C14 fragment. The preferred approaches to the syntheses of [1,2- 13 C 2 ]5,5-dichlorohexanoic acid 15 and the N-acetylcysteamine derivative of [1,2- 13 C 2 ]cinnamic acid 19 involved a Horner-Wadsworth-Emmons chain extension and Knoevenagel reaction, respectively.