Synthesis of highly functionalized δ-lactone-fused cyclopentanoids

A short and efficient route to δ-lactone-fused cyclopentanoids starting from the easily accessible Diels-Alder adducts between homoallylic alcohol acetates and 1,2,3,4-tetrachloro-5,5-dimethoxycyclopenta-1,3-diene is reported. Since homoallyl alcohols were derived from the corresponding aldehydes RCHO (R = alkyl, aryl) through allyl metal addition, the methodology is broad in scope with regard to the choice of R group. The initially formed 1:1 diastereomeric mixture of adducts were subjected to ruthenium-catalyzed oxidation followed by acid-mediated hydrolysis of the acetate groups to obtain the hemiacetals 6a-e. Alkaline H₂O₂-mediated cleavage of the hemiacetals led, after esterification with diazomethane, to a chromatographically separable diastereomeric mixture of 7 and 8 in high overall yield (54-68%).