FUNCTIONALIZED CARBOCYCLES FROM CARBOHYDRATES. PART 4. THE SYNTHESIS OF THE EPOXY LACTONE PROSTAGLANDIN INTERMEDIATE VIA BICYCLO(3.2.0)HEPTANE DERIVATIVES. X-RAY CRYSTAL STRUCTURE OF (1R)-5-ENDO-ACETYL-2-EXO,3-ENDO-BIS(BENZOYLOXY)BICY