1,2,3,4,5-Pentacarbomethoxycyclopentadiene (PCCP) is a strong organic acid and a precursor to useful organocatalysts, including chiral Brønsted acids and silicon-based Lewis acids. The synthetic route to PCCP, first reported in 1942, is inconvenient for a number of reasons. The two-step synthesis requires the purification of intermediates from intractable side-products, high reaction temperatures, and extensive labor (3 days). We have developed an improved procedure that delivers PCCP efficiently in 24 hours in one pot at ambient temperature and without isolation.

An enantio- and diastereoselective Rh-catalyzed conjugate addition reaction for the synthesis of proline analogues is reported. A high-throughput experimentation campaign was used to identify an efficient chiral catalyst which was able to afford the desired products in high yield and with high levels of diastereo- and enantioselectivity. This method was used to afford a range of 3-substituted proline derivatives from readily available dehydroproline electrophiles and boronic acid nucleophiles.