A C 2 ‐Chiral Bis(amidinium) Catalyst for a Diels−Alder Reaction Constituting the Key Step of the Quinkert−Dane Estrone Synthesis

A novel C 2 ‐chiral bis(amidinium) salt 12 has been synthesised from 5‐( tert ‐butyl)isophthalic acid. The hydrogen‐bond‐mediated association of dienophiles 3a and 3b with the chiral host molecule 12 accelerates the Diels−Alder reactions with diene 2 by more than three orders of magnitude. In addition, enantioselective formation of the desired adducts is observed under catalysis with 12 . Good ratios of 4a ( b ) + ent ‐ 4a ( b ) /5a ( b ) + ent ‐ 5a ( b ) from 1:10 to 1:22 were found in all reactions. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)