Oxabicycloheptanes and oxabicycloheptenes, their preparation and use

A compound having the structure

• wherein
• bond αis present or absent;
• R1 and R2 is each independently H, O−O or OR9,
• where R9 , is H, alkyl, alkenyl, alkynyl or aryl,
• or H1 and R2, together are ═O;
• R3 is OH
• R4 is
• R5 and R6 is each independently H, OH, or R5 and R6 taken together are ═O;
• and
• R7 and R8 is each independently H, F, Cl, Br, SO2Ph, CO2CH3, or SR13,
• where R13 is H, aryl or a alkyl, alkenyl or alkynyl,
• or a salt or enantiomer of the compound.