Epoxide formation by the photolysis of cyclic oxalate esters

The cyclic oxalate esters from $\text{meso}$- and $\text{d}$, $\text{1}$-hydrobenzoin were prepared and photolyzed. $\text{Meso}$-hydrobenzoin oxalate gave only $\text{cis}$-stilbene oxide upon photolysis while the $\text{d}$, $\text{1}$ isomer gave $\text{trans}$-stilbene oxide.