Synthesis of [28-¹³C]-24-methylenecholesterol using 1-tert-butyl-1H-tetrazol-5-yl [13C]-methyl sulfone to methylenate an isopropyl ketone intermediate

[28-C-13]-24-Methylenecholesterol, a labelled form of a phytosterol found in pollen that is a critical micronutrient for honey bees (Apis mellifera, L.), was prepared in six steps and 20% overall yield from 3 beta-hydroxy-5-cholenoic acid. The acid was converted to the corresponding isopropyl ketone via its TBS ether protected Weinreb amide derivative and the carbonyl group was subsequently methylenated (in 51% yield) by a Julia-Kocienski olefination using 1-tert-butyl-1H-tetrazol-5-yl [C-13]-methyl sulfone to introduce the C-13-labelled methylene carbon-atom. [GRAPHICS] .