Unexpected formation of a chiral δ-lactone by reduction of the 1,3-dicarbonylic cyclopentanoid derivatives

We have described the synthesis of highly functionalized chiral cyclopentanoids, which are important building units for synthesis of biological active compounds. The (−)- or (+)-7,7-dimethoxy-1,4,5,6-tetrachlorobicyclo[2.2.1]hept-5-en-2-endo-yl acetate, obtained from the enzyme catalyzed transesterification of the racemate, was converted to α-diketone chiral. The α-diketone was treated with H2O2/NaOH and esterified with CH2N2 to furnish a mixture of the compounds (+)- or (−)-10 and (+)- or (−)-11. The reduction of the (+)- or (−)-10 and/or (+)- or (−)-11 with BH3·THF furnished the lactone (+)- or (−)-13 with excellent yield. The α-diketone was reduced with indium metal in the presence of NH4Cl furnishing the acyloin (+)-14 in 67% of yield. The treatment of acyloin (+)-14 with Pb(OAc)4 furnished the aldehyde (+)-15 with 80% of yield. The reduction of the aldehyde (+)-15 with NaBH4 has again produced the lactone (+)-13.