A New Aspect of Magnesium Bromide‐Promoted Enantioselective Aryl Additions of Triaryl(tetrahydrofuran)aluminum to Ketones Catalyzed by a Titanium(IV) Catalyst of trans‐1,2‐Bis(hydroxycamphorsulfonylamino)cyclohexane

Abstract

A novel aspect of MgBr 2 -promoted asymmetric triarylaluminum-tetrahydrofuran [AlAr 3 A C H T U N G T R E N N U N G (THF)] additions to ketones catalyzed by a titanium catalyst of 20 mol% trans-1,2-bis(hydroxycamphorsulfonylamino)cyclohexane (2) is reported. The catalytic system works excellently for aromatic ketones with either an electron-withdrawing or an electrondonating substituent on the aromatic ring at the 2'-, 3'-, or 4'-positions, affording tertiary alcohols in excellent enantioselectivities of ! 90% ee, except for the cases of phenyl addition to 2'-methoxyacetophenone and 4-trimethylsilylphenyl (4-TMSC 6 H 4 ) addition to acetopheneone.

Highly Enantioselective Vinyl Additions of Vinylaluminum to Ketones Catalyzed by a Titanium(IV) Catalyst of (S)-BINOL

“…However, organoaluminum reagents were used in limited cases of asymmetric catalytic alkylation, allylation, allylic alkylation, and alkynylation reactions, achieving products in good to excellent enantioselectivies. Recently, our group demonstrated that the [AlAr 3 (THF)] reagents are efficient aryl nucleophiles for the additions to aldehydes and ketones catalyzed by titanium catalyst of ( R )-H 8 -BINOL, ( S )-BINOL (BINOL = 2,2′-dihydroxy-1,1′-binaphthyl), or sulfonamide alcohols. Furthermore, [AlAr 3 (THF)] is an effective coupling reagent with aryl halides .…”

Total Synthesis of the Antifungal Natural Product Mollisin

“…( S )‐1‐Phenyl‐1‐[3‐(trifluoromethyl)phenyl]ethanol (2f): 11a Compound 2f was obtained after purification by flash silica gel chromatography (hexane/EtOAc, 100:0 to 94:6) as a yellow viscous oil (50 % yield, 80 % ee ). [ α ] D 24 = +18.5 ( c = 1.0, CH 2 Cl 2 ) {ref.…”

Recent Advances in the Synthesis of Enantiomerically Enriched Diaryl, Aryl Heteroaryl, and Diheteroaryl Alcohols through Addition of Organometallic Reagents to Carbonyl Compounds

“…The chiral complex generated from dihydroxy bis-(sulfonamide) ligand 24 and Ti(OiPr 4 ), previously successfully used for phenylzinc 29a,b and arylzinc 29c addition to aldehydes, was used by the Gau group for the asymmetric AlAr 3 (THF) addition to ketones. 65 It was found that magnesium halide in an impure sample of AlAr 3 (THF) plays a key role in the promotion of the asymmetric catalytic reaction and improves both the yields and enantioselectivity. The effect of a variety of additives was examined to better understand the key role of the metal salts in the promotion of the reaction, and it was found that 48 mol% of MgBr 2 afforded the product with better results.…”