Application of a Planar Chiralη5-Cyclopentadienylrhenium(I)tricarbonyl Complex in Asymmetric Catalysis: Highly Enantioselective Phenyl Transfer to Aldehydes

Selective Synthesis of Ketones and Chiral Allylic Alcohols from the Addition of Arylboronic Acids to α,β-Unsaturated Aldehydes Mediated by a Transition Metal/Monophosphorus Ligand System

Here, we demonstrated a transition metal-mediated/monophosphorus ligand system for the selective synthesis of ketones or chiral allylic alcohols in high yields/enantiomeric excess from the 1,2-addition of arylboronic acids to α,β-unsaturated aldehydes. Notably, isomerization of the chiral allylic alcohols to ketones was suppressed by the Ru-catalyzed/monophosphorus ligand system. The asymmetric catalytic system provides an alternative and efficient method of preparing chiral allylic alcohols.

Nucleophilic Activation of Alkenyl and Aryl Boronates by a Chiral CuIF Complex: Catalytic Enantioselective Alkenylation and Arylation of Aldehydes

A new method for the catalytic enantioselective alkenylation and arylation of aldehydes involves the activation of alkenyl and aryl boronates by a catalytic amount of the Cu(I)F-DTBM-segphos complex through transmetalation, generating novel alkenyl and aryl copper species. These reagents act as the actual nucleophile. A range of aldehydes can be converted into optically active secondary allyl alcohols or diaryl methanols with excellent enantioselectivity. The appropriate choice of additives, depending on the substrate, is critical to ensure high yields of products. These additives possibly modulate the catalyst turnover step from copper alkoxide intermediates generated by the addition of organocopper reagents to aldehydes.

Asymmetric diethyl- and diphenylzinc additions to aldehydes by using a fluorine-containing chiral amino alcohol: a striking temperature effect on the enantioselectivity, a minimal amino alcohol loading, and an efficient recycling of the amino alcohol

A chiral pyrrolidinylmethanol derivative containing perfluoro-ponytails (5) was prepared from (S)-proline. The use of this perfluoro-substituted amino alcohol in catalytic asymmetric additions of organozinc reagents to aldehydes affords products with high enantioselectivities in both pure hexane and a mixture of hexane and FC-72 (perfluorohexane). Enantiomeric excesses up to 94 and 88 % ee have been achieved in Et(2)Zn and Ph(2)Zn additions, respectively. For the reactions in the biphasic solvent system a striking temperature effect was observed. Thus, when the temperature was raised from 0 to 40 degrees C the ee value of the product increased from 81 to 92 %. Furthermore, the catalyst loading could be remarkably low, and with only 0.1 mol % of amino alcohol 5 a product with 90 % ee was obtained in the Et(2)Zn addition to benzaldehyde in hexane. The perfluoro-ligand was easily recovered by simple phase separation, and until the ninth repetition its reuse proceeded without significant loss of enantioselectivity and reactivity.

Highly Enantioselective Addition of In Situ Prepared Arylzinc to Aldehydes Catalyzed by a Series of Atropisomeric Binaphthyl-Derived Amino Alcohols

The direct addition of in situ prepared arylzinc to aldehydes with chiral binaphthyl-derived amino alcohols as catalysts can afford optically active diarylmethanols in high yields and with excellent enantioselectivities (up to 99 % ee, ee = enantiomeric excess). By using a single catalyst, both enantiomers of many pharmaceutically interesting diarylmethanols can be obtained by the proper combination of various arylzinc reagents with different aldehydes; this catalytic system also works well for the phenylation of aliphatic aldehydes to give up to 96 % ee.

A New Efficient Route to Chiral 1,3-Disubstituted Ferrocenes: Application to the Syntheses of (Rp)- and (Sp)-17α-[(3′-formylferrocenyl)ethynyl]estradiol

Starting from (2S,4S)-2-ferrocenyl-4-(methoxymethyl)-1,3-dioxane (4), use of the stereogenic ortho-directing menthyl para-tolyl sulfoxide group, which occupies the 2' position in the ferrocenyl ring and redirects subsequent lithiation to the 3' position, allowed the synthesis of optically pure (S(p))-1-formyl-3-iodoferrocene (8), that was characterized by single-crystal X-ray diffraction. Combination of this method with a protection-deprotection strategy, using trimethylsilyl as a temporary blocking group, yielded (R(p))-1-formyl-3-iodoferrocene (13). Separate Sonogashira coupling of each of the enantiomeric iodoformylferrocenes 8 and 13 with 17alpha-ethynyl-estradiol produced (R(p))-17alpha-[(3'-formylferrocenyl)ethynyl]estradiol (14) and (S(p))-17alpha-[(3'-formylferrocenyl)ethynyl]estradiol (15), respectively.

Resolution of Racemic 2-Aminocyclohexanol Derivatives and Their Application as Ligands in Asymmetric Catalysis

A preparatively easy and efficient protocol for the resolution of racemic 2-aminocyclohexanol derivatives is described, delivering both enantiomers with >99% enantiomeric excess (ee) by sequential use of (R)- and (S)-mandelic acid. A simple aqueous workup procedure permits the isolation of the amino alcohols in analytically pure form and the almost quantitative recovery of mandelic acid. Debenzylation of enantiopure trans-2-(N-benzyl)amino-1-cyclohexanol by hydrogenation and subsequent derivatization give access to a broad variety of diversely substituted derivatives. Furthermore, the corresponding cis isomers are readily available. Applications of these optically active aminocyclohexanols in catalyzed asymmetric phenyl transfer reactions to benzaldehydes and transfer hydrogenations of aryl ketones lead to products with up to 96% ee.

Catalyzed Asymmetric Arylation Reactions

Addition and substitution reactions with carbon nucleophiles are fundamental processes in organic synthesis, and the development of general catalytic asymmetric variants thereof is still a major challenge today. In contrast to enantioselective alkyl transfer reactions, the corresponding arylations have not yet reached a high level of maturity. The existing protocols are either of no general applicability or are limited in terms of selectivity. This article summarizes established routes for catalytic asymmetric aryl transfer together with the latest developments in this area. The scope and limitations of this reaction are discussed.