Efficient synthesis of the odourant, 2-nonen-4-olide

A three-step synthesis of 2-nonen-4-olide starting from heptanal is reported. (E)-3-Nonenoic acid, prepared by Knoevenagel condensation of malonic acid and heptanal, was oxidised by performic acid, a process accompanied by lactonisation, to give 3-hydroxynonan-4-olide in 85% yield. This lactone when reacted with MsCl in the presence of Et3N gave, by elimination, 2-nonen-4-olide in 88% yield. The overall yield was 75%. The odour of the product was evaluated by GC-olfactory analysis and sniffing blotter confirming an oily, coconut-like, and rancid odour.