Straightforward, Metal-free, and Stereoselective Synthesis of 9-Oxo- and 10-Hydroxy-2(E)-decenoic acids, Important Components of Honeybee (Apis mellifera) secretions

10-Hydroxy-2E-decenoic (10-HDA) and 9-oxo-2E-decenoic (9-ODA) acids, two components identified in honeybee secretions, have both received considerable recent interest due to their involvement in caste switch and maintenance. Herein we report for the first time a metal-free, gram scale, and stereoselective synthesis of these honeybee secretion components by TEMPO catalyzed oxidation of readily available alcohols and subsequent Doebner-Knoevenagel reactions between the resulting aldehydes and malonic acid. Mechanistic investigations undertaken highlighted the crucial role of the Doebner-Knoevenagel reaction in the high yielding and selective preparation of the [small alpha],[small beta]-unsaturated acids 10-HDA and 9-ODA. The combination of inexpensive and environmentally friendly reagents with simple synthetic procedures renders this approach a valuable green strategy for the gram scale preparation of these biologically relevant natural molecules