Preparation and characterization of new C 2- and C 1-symmetric nitrogen, oxygen, phosphorous, and sulfur derivatives and analogs of TADDOL. part III

Abstract

A brief overview is presented of the field of organocatalysis using chiral H-bond donors, chiral Brønsted acids, and chiral counter-anions (Fig. 1). The role of TADDOLs (=α,α,α′,α′-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). pK a Measurements of TADDOLs and analogs in DMSO (reported in the literature; Fig. 5) and in MeO(CH 2) 2OH/H 2O (described herein; Fig. 6) provide information about further possible applications of this type of compounds as strong chiral Brønsted acids in organocatalysis. Copyright © 2012 Verlag Helvetica Chimica Acta AG, Zürich, Switzerland.