Preparation and Characterization of New C2-and C1-Symmetric Nitrogen, Oxygen, Phosphorous, and Sulfur Derivatives and Analogs of TADDOL. Part III

A brief overview is presented of the field of organocatalysis using chiral H-bond donors, chiral Bronsted acids, and chiral counter-anions (Fig. 1). The role of TADDOLs (=alpha,alpha,alpha',alpha'-tetraaryl-1,3-dioxolane-4,5-dimethanols) as H-bond donors and the importance of an intramolecular H-bond for acidity enhancement are discussed. Crystal structures of TADDOLs and of their N-, S-, and P-analogs (Figs. 2 and 3) point the way to proposals of mechanistic models for the action of TADDOLs as organocatalysts (Scheme 1). Simple experimental two-step procedures for the preparation of the hitherto strongest known TADDOL-derived acids, the bicyclic phosphoric acids (2 in Scheme 2) and of a phosphoric-trifluorosulfonic imide (9 in Scheme 4), are disclosed. The mechanism of sulfinamide formation in reactions of TADDAMIN with trifluoro-sulfonylating reagents is discussed (Scheme 3). pKa Measurements of TADDOLs and analogs in DMSO (reported in the literature; Fig. 5) and in MeO(CH2)2OH/H2O (described herein; Fig. 6) provide information about further possible applications of this type of compounds as strong chiral Bronsted acids in organocatalysis.