Preparation and some reactions of α,β‐unsaturated lactones synthesis of cyclopropanes related to chrysanthemic acid

2-Bromo-2-methylpropylidene malonates, 3, undergo thermal ringclosure reactions to give 3-alkoxycarbonyl-5,5-dimethyl-2(5H)-furanones, 4. Michael addition of Grignard reagents and thiols to 4a, subsequent ethoxycarbonyl elimination, treatment of 8 with SOCl2 and EtOH and, finally, ringclosure lead to cyclopropanes. Sodium cyanide is also smoothly added to 4a. Addition of NaCN, C2H5ONa and ϕSNa to 3 gives the cyclopropanes, 17. Subsequent ethoxycarbonyl elimination of 17a produces 18a and 19a, which are related to chrysanthemic acid.