Enantioselective synthesis of sec-allylalcohols by catalytic asymmetric addition of divinylzinc to aldehydes.
TL;DR: Readily available chiral tridentate ligand 8 catalyzes the highly Si-face selective addition of diethyl-, di-n-propylzinc and, more significantly, of divinylzinc to aromatic and aliphatic aldehydes whereas bidentates 11 and 12 exert a topologically reversed catalytic bias as mentioned in this paper.
About: This article is published in Tetrahedron Letters.The article was published on 1988-01-01. It has received 133 citations till now. The article focuses on the topics: Enantioselective synthesis & Addition reaction.
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TL;DR: These studies on macromolecular chiral catalysts demonstrate that these materials are potentially very useful for practical applications and can also be preserved in the rigid and sterically regular polymer provided the catalytically active species of the monomer catalyst is not its aggregate.
Abstract: Because of the tremendous effort of a great number of researchers, the catalytic asymmetric dialkylzinc addition to aldehydes has become a mature method. Ligands of diverse structures have been obtained, and high enantioselectivity for all different types of aldehydes have been achieved. Among the representative excellent catalysts are compounds 1, 8, 120, 325, 352, and 360 discussed above. However, compared to the well-developed dialkylzinc addition, the catalytic asymmetric reactions of aryl-, vinyl-, and alkynylzinc reagents with aldehydes are still very much under developed. Although catalysts such as (S)-402 and 210 prepared by Pu and Bolm have shown good enantioselectivity for the reaction of diphenylzinc with certain aromatic and aliphatic aldehydes, the generality of these catalysts for other [formula: see text] arylzinc reagents have not been studied. The vinylzinc additions using ligands 1 and 412 reported by Oppolzer and Wipf were highly enantioselective for certain aromatic aldehydes but not as good for aliphatic aldehydes. Carreira discovered highly enantioselective alkynylzinc additions to aldehydes promoted by the chiral amino alcohol 415, but this process was not catalytic yet. Ishizaki achieved good enantioselectivity for the catalytic alkynylzinc addition to certain aldehydes by using compounds 160, but the enantioselectivity for simple linear aliphatic aldehydes was low. Another much less explored area is the organozinc addition to ketones. Yus and Fu showed very promising results by using ligands 381 and 406 for both dialkylzinc and diphenylzinc additions to ketones, but the scope of these reactions were still very limited. Therefore, more work is needed for the aryl-, vinyl-, and alkynylzinc additions and for the organozinc addition to ketones, although many good catalysts have been obtained for the dialkylzinc addition to aldehydes. Development of these reactions will allow the catalytic asymmetric synthesis of a great variety of functional chiral alcohols that are either the structural units or synthons of many important organic molecules as well as molecules of biological functions. Macromolecular chiral catalysts have become a very attractive research subject in recent years because these materials offer the advantages of simplified product isolation, easy recovery of the generally quite expensive chiral catalysts, and potential use for continuous production. Three types of macromolecules including flexible achiral polymers anchored with chiral catalysts, rigid and sterically regular main chain chiral polymers, and chiral dendrimers have been used for the asymmetric organozinc addition to aldehydes. Among these materials, the binaphthyl-based polymers such as (R)-451 developed by Pu have shown very high and general enantioselectivity. Study of the binaphthyl polymers in the asymmetric organozinc addition has demonstrated that it is possible to systematically modify the structure and function of the rigid and sterically regular polymer for the development of highly enantioselective polymer catalysts. The catalytic properties of highly enantioselective monomer catalysts can also be preserved in the rigid and sterically regular polymer provided the catalytically active species of the monomer catalyst is not its aggregate. The TADDOL-based polymers and dendrimers prepared by Seebach showed very high and stable enantioselectivity for the diethylzinc addition to benzaldehyde even after many cycles. These studies on macromolecular chiral catalysts demonstrate that these materials are potentially very useful for practical applications.
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TL;DR: The plethora of methods developed for the catalytic asymmetric synthesis of enantioenriched allylic alcohols, including dynamic kinetic resolution (DKR/DKAT), nucleophilic 1,2-addition to carbonyl groups, allylic substitution, oxidation of C-H bonds, and the addition of O nucleophiles to π systems are summarized.
Abstract: Allylic alcohols represent an important and highly versatile class of chiral building blocks for organic synthesis. This Review summarizes the plethora of methods developed for the catalytic asymmetric synthesis of enantioenriched allylic alcohols. These include: dynamic kinetic resolution (DKR/DKAT), nucleophilic 1,2-addition to carbonyl groups, allylic substitution, oxidation of CH bonds, the addition of O nucleophiles to π systems, reduction of unsaturated carbonyl compounds, and an alternative route from enantioenriched propargylic alcohols. Furthermore, these catalytic asymmetric processes are exemplified by their applications in the syntheses of complex molecules such as natural products and potential therapeutic agents.
229 citations
TL;DR: In this paper, a katalytischen enantioselektive alkylierung von Aldehyden is described, which verlauft uber einen zweikernigen Zinkkomplex, der ein chirales Aminoalkoxid, den AldeHyd and drei Alkylreste als Liganden enthalt.
Abstract: Die nucleophile Addition von Organometallreagentien an Carbonylverbindungen ist eine der grundlegendsten Operationen der Organischen Synthese. Eine Modifizierung der Organometallkomponente durch chirale, nichtracemische Hilfsstoffe eroffnet einen allgemeinen Zugang zu optisch aktiven Alkoholen, wobei im besonderen die Leistungsfahigkeit der katalytischen Variante beeindruckend ist. Anders als die herkommlichen Organolithium- oder Organomagnesiumreagentien ermoglichten Organozinkverbindungen eine ideale katalytische enantioselektive Alkylierung von Aldehyden, die zu einer breiten Palette von sekundaren Alkoholen hoher optischer Reinheit fuhrte. Die besten Ergebnisse (bis zu 99% ee) liefert eine Kombination von Dialkylzinkverbindungen mit bestimmten sterisch uberfrachteten β-Dialkylaminoalkoholen wie (—)-3-exo-Dimethylaminoisoborneol [(—)-DAIB] als Trager der Chiralitatsinformation. Die Alkylubertragung verlauft uber einen zweikernigen Zinkkomplex, der ein chirales Aminoalkoxid, den Aldehyd und drei Alkylreste als Liganden enthalt. Die Methode der Chiralitatsvervielfaltigung ermoglicht eine enorme Chiralitatsverstarkung. So kann durch Einsatz von (—)-DAIB mit 14% ee eine Enantioselektion bis zu 98% erzielt werden. Dieser ungewohnliche nichtlineare Effekt kann darauf zuruckgefuhrt werden, das sich die diastereomeren (homochiralen und heterochiralen) zweikernigen Komplexe aus Dialkylzinkverbindung und dem Hilfsstoff DAIB in ihren chemischen Eigenschaften stark unterscheiden. Moglicherweise markiert dieses Phanomen den Beginn einer neuen Generation enantioselektiver organischer Reaktionen.
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TL;DR: The reaction of diethylzinc with benzaldehyde catalyzed by a small amount of chiral 2-amino-1-alcohols in toluene at room temperature gave optically active 1-phenylpropan-1ol almost quantitatively in ∼, 50% ee as discussed by the authors.
296 citations