Arylation catalytic enantioselective

The majority of catalytic enantioselective allylation reactions involve the chiral Lewis-acid-catalysed additions of allylsilanes or allylstannanes to carbonyl compounds. Monothiobinaphthol has been used by Woodward et al. as a chiral promoter in the enantioselective catalytic allylation of aryl ketones with impure Sn(allyl)4, prepared from allyl chloride, air-oxidised magnesium and SnCl4. Therefore, the allylation of arylketones in these conditions was achieved very efficiently, since the corresponding allylic alcohols were formed in... 

Catalytic enantioselective crossed aldehyde-ketone benzoin cyclizations of ketoaldehydes, such as 13, readily obtained from an aryl nitrile oxide and a 1,3-diketone, were studied in order to perform the synthesis of complex molecules. Significant asymmetric induction was observed with chiral triazolium salts such as 14, in the presence of DBU as base, leading to compound 15 in high yield and with 99% ee in favor of the R enantiomer <06AG(E)3492>. 

Reactions of organometallic derivatives with ketones, which are less electrophilic than aldehydes, usually require an equimolar amount of a chiral ligand. The first catalytic enantioselective addition of an organometallic reagent, namely ZnPh2, to dialkyl and aryl alkyl ketones was reported in 1998 by Dosa and Fu (Scheme 110).288 The procedure... 

Table 9.7 Catalytic enantioselective oxidation of aryl alkyl sulfides 2 with hydrogen peroxide in water-SDS solution mediated by 1...

A catalytic enantioselective arylation of arylaldehydes employs a chiral /3-amino alcohol and a boronic acid-diethylzinc exchange reaction to generate the reactive arylzinc species.247... 

An easy and simple synthesis of different chiral fran -l-arenesulfonylamino-2-isoborneolsulfonylaminocyclohexane derivatives (41) has been reported.108 These ligands have proved to be excellent promoters for the catalytic enantioselective alkylation and arylation of ketones (up to 99% ee), very good for the alkenylation process, and modest for the allylation and alkynylation reactions. 

Another important means of mediation of metal-free catalytic enantioselective Mannich-type reactions is via electrophilic activation of the preformed imines by chiral Bronstedt acids [7, 8, 46], By using this strategy Terada and coworkers performed chiral phosphoric acid-catalyzed direct asymmetric Mannich-type reactions between Boc-protected imines and acetoacetone that furnished aryl /3-amino... 

The catalytic enantioselective addition of aromatic C - H bonds to alkenes would provide a simple and attractive method for the formation of optically active aryl substituted compounds from easily available starting materials. The first catalytic, highly enantioselective Michael addition of indoles was reported by Jorgensen and coworkers. The reactions used a,fl-unsaturated a-ketoesters and alkylidene malonates as Michael acceptors catalyzed by the chiral bisoxazoline (BOX)-metal(II) complexes as described in Scheme 27 [98,99]. 

The most intriguing work in the field of asymmetric oxidative aryl coupling has been directed towards finding catalytic enantioselective reactions. The main goal in these studies has been the synthesis of chiral binaphthyl units as an improvement over stoichiometric chiral reagent enantioselective syntheses. 

Chiral Bronsted acids can also promote the asymmetric addition of allylic tin reagents to carbonyl compounds. Baba and coworkers have found that a stoichiometric amount of (fl)-BINOL (37) acts a chiral promoter for the allylation of unactivated ketones with tetraallyltin and in the presence of MeOH, the corresponding nonracemic tertiary homoallylic alcohols are obtained with up to 60% ee [50]. Later, Woodward et al. improved this process and achieved a catalytic enantioselective allylation of aryl ketones by employing (fl)-monothio-binaphthol 36 as a chiral Bronsted catalyst [49]. For instance, in the presence of 20 mol% of the chiral acid 36 and 40 mol% of H20 in toluene, acetophenone (42) was allylated by a 0.7 0.3 mixture of tetraallyltin (41) and butyltriallylltin (55) to give the (jR)-enriched allylated product 56 almost quantitatively with 89-86% ee (Scheme 8). 

Other organometallic compounds, including aUylic stannanes, allylic samarium, allylic germanium, and allylic indium compounds add to aldi-mines in the same manner. Aryltrialkylstannanes also add the aryl group to Al-tosyl imines using a rhodium catalyst and sonication. Catalytic enantioselective addition reactions are well known, including reactions in an ionic liquid.Allylic... 

Finally, Elhnan has recently developed a method for the synthesis of a-aryl,-aryl substituted primary amines using the corresponding A-t-butanesulfmyl aldimine (chiral auxiliary approach) or via an N-diphenylphosphinoyl aldimine (catalytic enantioselective method) using an arylboronic acid in combination with chiral Rh catalysts. ... 

Zhang Catalytic Enantioselective N-acyl-a-Aryl-Enamide Reductions... 

Kiely, D. and Guiry, PJ. (2003) Palladium complexes of phosphinamine ligands in the intramolecular asymmetric Heck reaction. Journal of Organometallic Chemistry, 687, 546-561. Dounary, A.B., Hatanaka, K., Kodanko, J.J. et al. (2003) Catalytic asymmetric synthesis of quaternary carbons bearing two aryl substituents. Enantioselective synthesis of 3-alkyl-3-aryl... 

The catalytic enantioselective formation of C—C bonds is one of the most fundamental processes in modern organic synthesis for the rapid construction of complex molecules. Arylation methods have their special place in this area due to the importance of aromatic groups in numerous pharmaceuticals (Figure 8.1) [1]. Considerable research endeavors have been undertaken during the past few years in order to optimize existing protocols and widen the scope of molecules that can be accessed. Since the publication by Bohn, in 2001, of a review of catalytic asymmetric arylation reactions, many innovative and practical processes have been developed for the straightforward enantioselective, catalytic introduction of aryl groups [2]. 

Most of the catalytic enantioselective protocols are limited to aryl aldehydes as substrates. Pu recently disclosed a process involving chiral bifunctional ligand 6 which is perfectly suited for additions to aliphatic aldehydes (7). Traditionally used aryl aldehydes were also converted under the reported conditions. 

Pioneering studies of the catalytic, enantioselective arylation of imines date back to 2000, when Hayashi disclosed a rhodium/phosphine-catalyzed addition of arylstannanes to N-tosylarylimines (31). Whereas, the method gave rise to highly enantioenriched diarylmethylamines, five equivalents of the stannane were required to obtain high yields. 

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