One solution to the problem of oxidation is to replace the hydrogens ortho to the carbon-carbon double bond by groups that can not be removed during the oxidation. Following the Woodward–Hoffmann rules, the photochemical 6π cyclization takes place in a conrotatory fashion, leading to products with an anti configuration of the methyl substituents. As both methyl groups are attached to a stereogenic center, two enantiomers (R,R and S,S) are formed, normally as a racemic mixture. This approach also has the advantage that the thermal (disrotatory) ring closure can not take place because of steric hindrance between the substitution groups.