Two novel cross-linked polystyrene-supported N-sulfonylated β-aminoalcohol resins 94 and 95 have been prepared from radical co-polymerizations of styrene, divinylbenzene, and styrenes bearing a para-substituent of N-sulfonylated aminoalcohol. Resins 94 and 95 were obtained in high yields of 85.8 and 84.7%, and were characterized by IR and solid state 13C NMR spectroscopy. Elemental analyses reveal that one gram of the resin 94 contains 0.93 mmol bidentate N-sulfonylated β-aminoalcohol. The ligand content in the tridentate resin 95 is calculated to be 0.95 mmol/g. The Ti(O-i-Pr)4/94 catalytic system works excellently in asymmetric ZnEt2 additions to aldehydes affording secondary alcohols in ≥90% ee. The resin 94 can be reused 9 times without losing any activity, giving the product with enantioselectivities ≥87% ee. The Ti(O-i-Pr)4/95 system was used only once in asymmetric AlEt3 additions to a variety of aldehydes affording secondary alcohols in good to excellent enantio- selectivities from 73 to 92% ee. Novel asymmetric aryl additions of AlAr3(THF) to ketones catalyzed by the titanium catalyst of (S)-BINOL are reported. A wide variety of ketones are examined to afford products, in general, in excellent enantioselectivities of ≥90% ee for aromatic ketones bearing either an electron-donating or an electron-withdrawing substituent at 2’-, 3’-, or 4’-position on the aromatic ring. Steric effects are found for additions to ortho-substituted aromatic ketones with longer reaction times required to give products in higher yields. The catalytic system applies also to α,β-unsaturated ketones and 2-acetylfuran to give products in good to excellent enantioselectivities. More importantly, aluminum reagents with different aryl nucleophiles can be easily prepared for additions to aromatic ketones furnishing tertiary diaryl alcohols in both absolute configurations. Asymmetric AlPh3(THF) additions to ketones catalyzed by the titanium catalyst of 20 mol% trans-1,2-bis(hydroxycamphorsulfonylamino)cyclohexane (116) are now reported. Several important features were demonstrated in this study. First, a novel aspect of inorganic salt of MgBr2 as a key additive to promote the phenyl addition of AlPh3(THF) to ketones was demonstrated. Second, the catalytic system worked excellently for aromatic ketones bearing either an electron-withdrawing or an electron-donating substituent on the aromatic group to afford tertiary alcohols in enantioselectivities of ≥90% ee except for 2’-methoxyacetophenone. Third, longer reactions times were required for ortho-substituted aromatic ketones to furnish products in good yields. Based on these results, we propose that MgBr2 binds to the sulfonamide oxygen atom, thereby freeing a coordination site for the ketone substrate. A series of background, stoichiometric, and catalytic phenyl addition reactions are tested for aldehydes and ketones. TiPh(O-i-Pr)3 exists in the catalytic system, as confirmed by 1H NMR study and X-ray diffraction. These results indicate that TiPh(O-i-Pr)3 plays a key role in the catalytic reactions, yielding high enantio- selectivities. Ti2Ph(BINOLate)(O-i-Pr)5 (176) is synthesized by mixing Ti(BINOLate)- (O-i-Pr)2 and TiPh(O-i-Pr)3, and characterized by X-ray diffraction. Observation of the structure of complex 176 reveals a pocket on the same side of the bridging isopropoxide. Aldehydes and ketones apparently access the Ti(1) metal center from the top of the pocket to form a six-coordinate metal center, and the substrates then would appear to be placed in the proper orientation for achieving the excellent enantioselectivities. Thus, a catalytic cycle is depicted to illustrate the Ti(O-i-Pr)4/AlPh3(THF) asymmetric catalytic addition reactions with aldehydes or ketones.
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