Synthesis, structure and activity of sulfonamides derived from (+)-camphor in the enantioselective addition of diethylzinc to benzaldehyde

New chiral sulfonamides derived from (+)-camphor, with different substituents on camphor C2 and sulfonamide N, were synthesized. Their activity was tested in the reaction of Et2Zn addition to benzaldehyde. The yield of the reaction was 44–96%, the enantiomeric excess was 1–69%. Sulfonamides possessing the 2-hydroxyl group gave an excess of 1-(S)-phenylpropanol, while catalysts containing other sulfonamides gave 1-(R)-phenylpropanol as a major product. The best catalytic efficacy was observed for sulfonamides with (R)-C2–OH group, while the use of thioketo- and mercaptosulfonamides resulted in low enantiomeric excess and yields not exceeding 60%. Crystal structures have been determined for sulfonamides with N-benzyl moiety and different substituents on the C2 atom. The structural analysis revealed the presence of intramolecular N⋯O(C2) and Osulfo⋯O(C2) H-bonds, what confirms the ability of these molecules to adopt the conformation required for their bidentate coordination to Ti(IV) via the sulfonamide group and substituent at C2. The coordination mode for investigated sulfonamides was determined with the IR spectra for five obtained Ti(IV) complexes and crystal structure analysis of the ligands. The 3D structures of Ti(IV) complex catalysts containing investigated sulfonamides were postulated, which are consistent with the reported chirality of the addition product and observed % ee.

New sulfonamide auxiliaries derived from (+)-camphor were used in the Et2Zn addition to benzaldehyde (1–69% ee). 3D structures of Ti(IV) complexes were postulated, explaining observed % ee and product chirality.Figure optionsDownload high-quality image (106 K)Download as PowerPoint slide