Asymmetric Diels-Alder Reaction of 1-(S_R)-p-Tolylsulfinyl-3-penten-2-one with Cyclopentadiene Catalzed by a Chiral Titanium Reagent

Double asymmetric Diels-Alder reaction of 1(SR)-p-Tolylsulfinyl-3-penten-2-one with cyclopentadiene using a chiral titanium reagent was performed. The diastereoselectivity dependent on the size of aryl substituent involved in the chiral ligands was discussed Absolute configuration of the cycloadducts was conformed. Dramatic reversal of selectivity is observed.

Synthesis of Chiral 2,5-Bis(oxazolinyl)thiophenes and Their Application as Chiral Shift Reagents for 1,1′-Bi-2-naphthol

A series of C_2-symmetrical chiral 2,5-bis(4'-alkyloxazolin-2-yl) thiophenes(thiobox) have been synthesized from thiophene-2,5-dicarboxylic acid by sequential amidation with achiral ethanolamine, conversion of hydroxyl to chloro group, and base-promoted oxazoline ringformation. As demonstrated by (-)-2,5-bis[4'-(S)-isopropyloxazolin-2'-yl] thiophene, these thioboxsystems exhibited remarkable chirality recognition of 1,1'-bi-2-naphthol giving rise to pronouncedshifts in the ~1H NMR signals of the latter axial chiral compound at the positions of C-3, C-4, C-5,and C-8.

Study on synthesis of lanthanide chelates of (l)-α- trifluoromethyl-polyfluoroalkyl-β-diketone and their application as chiral shift reagents

The lanthanide chelates of(l)-2,2-dimethyl-6-trifluoromethyl-7-oxa-6,8,8,9,9,10, 10,10-octafluoro-3,5-decanedione,Ln[(l)-CF_3CF_2CF_2OCF(CF_3)COCHCOC(CH_3)_3]_3(l-3a,Ln=Eu; 3b, Ln=Pr), are useful as ~1H NMR shift reagents for direct determination of enantiomeric composition of enantiomorphous alcohols. ketones and amines. With these substrates. l-3a induces shift difference similar to that induced by Eu(facam)_3 and Eu(hfbc)_3. However, due to the higher solubility of the chelates l-3a and l-3b in nonpolar organic solvent such as CHCl_3, CCl_4 and only one ~1H signal from l-3a and l-3b is observed. their application as the new chiral shift reagents seems promising. The spectral nonequivalence is also observed for dimethylsulfoxide in the presence of l-3a.

Enantioselective allylation of aldehydes with chiral allyl organolanthanide reagents

The first example of enantioselective allylation of aldehydes with chiral allyl organolanthanide reagents has been achieved in high chemical yield and moderate optical purity (up to 54% e.e.).

Copper-Catalyzed Highly Enantioselective 1,4-Protoboration of Terminal 1,3-Dienes

The copper-catalyzed,highly enantioselective 1,4-protoboration of terminal 1,3-dienes with proton source and B2Pin2 has been developed.Chiral allylic boronate reagents,which are significant precursors for many well-established transformations,were prepared by this novel method with good functional group tolerance and enantioselectivity.Further studies indicated the products could be used as versatile precursors for asymmetric transformations and natural products syntheses.The mechanism of this reaction was investigated by control and reaction monitoring experiments.

Asymmetric catalytic anhydride openings via carbon-based nucleophiles

The asymmetric desymmetrization of cyclic anhydrides via the addition of carbon-based nucleophiles has been the focus of considerable levels of interest because it leads to optically active products. Over the past 20 years, a variety of different catalytic asymmetric alkylation reactions have been developed for the desymmetrization of cyclic anhydrides using different metal reagents as nucleophiles and using chiral ligands. The purpose of this review is to provide an overview of significant developments in this field. ~ 2013 Fen-Er Chen. Published by Elsevier B.V. on behalf of Chinese Chemical Society. All rights reserved.