An improved synthesis of ethyl cis-5-iodo-trans-2-methylcyclohexanecarboxylate, a potent attractant for the Mediterranean fruit fly

Both racemic ethyl 5-iodo-2-methylcyclohexanecarboxylate (), known as Mediterranean fruit fly attractant ceralure B1, and its (−)-(1R,2R,5R) enantiomer were conveniently synthesized from commercially available racemic trans-6-methyl-3-cyclohexenecarboxylic acid or its (1R,6R) enantiomer . Key steps included an asymmetric Diels–Alder reaction using a sultam auxiliary and cyclization of the unwanted trans-5-iodo-trans-2-methylcyclohexanecarboxylic acid () to the intermediate lactone (or ). The new method may circumvent chromatographic separations and seems amenable to scale-up.