Abstract The bicyclic hydroxy γ-lactone, cis-(-)-4 α-hydroxy-6, 6-dimethyl-3-oxa-bicyclo (3, 1, 0)-hexan-2-one (1), commonly known as 1R-cis-caronaldehyde, is an important intermediate for the highly potent pyrethroids Deltamethrin (2) and NRDC 182 (2). The latter is the biologically active isomer in commercial cypermethrin. In our laboratory we have obtained excellent yields of (1) by the reductive ozonolysis2 of the enol lactone 4 obtained ...