Scheme 5 illustrates an example for the stereocontrolled formation of quaternary stereocenter using chiral Rh₂ (S-PTTL)₄ catalyzed carbenoid C-H insertion process.

Scheme 5

The above catalytic system is also effective for the desymmetrization of aryl-substituted diazo ketoesters (Scheme 6). This reaction proceeds via electrophilic aromatic substitution and turnover numbers of up to 98000 have been achieved.

Scheme 6