DMAP catalyst

For example, a range of aryl alkyl xec-alcohols could be resolved in a highly efficient way using pentaphenylcyclopentadienyl 4-DMAP catalyst 16 (1-2 mol%) in conjunction with Ac O (0.75 eq) as the acyl donor and EtjN (0.75 eq) as an auxiliary... 

Fig. 4 Fu s concept for a planar-chiral 4-DMAP catalyst based on his pyrrole planar-chiral ...

Eu s planar chiral ferrocenyl 4-DMAP catalyst 16 was also shown to be effective for the ASD of mei o-diols as illustrated for the case of unusual meso-diol 22 (Scheme 9) [81]. 

Scheme 9 ASD of meso-didls catalyzed by Fu s 4-DMAP catalyst 16 [81]...

Analogous rearrangements have also been performed by both Fu [73] and Vedejs [105] on (9-acyl benzofuranones and (9-acyl oxindoles to provide synthetic intermediates potentially suitable for elaboration to diazonamide A and various oxin-dole-based alkaloids such as gelsemine respectively. Peris has also examined both Fu s and Vedejs chiral 4-DMAP catalysts for effecting diastereoselective carboxyl migrations of 3-arylbenzofuranones [109]. 

For a recent optimized derivative of the DMAP catalyst, see M. R. Heinrich, H. S. Klisa, H. Mayr,... 

Fu s planar chiral ferrocenyl DMAP catalyst 4b and also Vedejs PBO catalysts, particularly p-phenyl-PBO catalyst 2a, are also effective for this type of ASD reaction, as illustrated for the cases of unusual meso-diol 37 [49] and meso-hydrobenzoin [165], respectively (Scheme 8.19). 

This process proceeds as a DKR [13, 190] because the DMAP catalyst promotes not only the asymmetric alcoholysis of the azlactone but also its racemization under the reaction conditions the N-benzoyl a-amino acid ester product does not racemize under these conditions. Johannsen has also screened chiral DMAP 21 (Fig. 8.4) for this transformation, but obtained poorer yields and selectivities [102],... 

KR of an Aryl Alkyl sec-Alcohol with Ferrocenyl DMAP Catalyst ... 

R. Muragan, E. F. V Scriven, Applications of Dialkylaminopyridine (DMAP) Catalysts in Organic Synthesis, Aldrichim. Acta 2003, 36, 21-27. 

DCP as a Chiral Controller in Oxidative Free Radical Cyclizations. As a chiral auxiliary, DCP (1) is also reported to induce modest diastereoselection (60% de) in Mn(III)-based oxidative free-radical cyclizations of p-keto esters (eq 12). Chiral p-keto ester 25 was prepared by transesterification reaction with methyl ester 23, 1, and 0.3 equiv of DMAP (catalyst) in anhydrous toluene at reflux for 3-5 d as described by Taber. Oxidative cyclization of a 0.1 M solution of 24 in AcOH with 2 equiv of Mn(OAc)3-2HzO and 1 equiv of Cu(OAc)3 HzO provided bicyclo[3.2.1]octan-2-one (25). 

In 1993, Vedejs et al. [5,6] showed that tributylphosphine is a potent catalyst for the acylation of alcohols by acetic and benzoic anhydrides as efficient as 4-(di-methylamino)pyridine DMAP [7,8]. However, the DMAP catalyst is more versatile since it presents catalytic activity in the reaction of alcohols with a larger variety of electrophiles. Due to these properties, Fu [9] realized the design and synthesis of a new family of chiral nucleophilic catalysts illustrated by the planar-chiral DMAP derivative I which is a very efficient catalyst in different enantioselective reactions such as addition of alcohols to ketenes [10], rearrangement of O-acylated azalactones [11], and kinetic resolution of secondary alcohols [12-14]. 

Attachment and deavage To resin 173 were added DIC (3 equiv.), Fmoc-P-alanine (3 equiv.), DIEA (3 equiv.), DMAP (catalyst), and HOBt (catalyst) in DMF. The yield for the esterification was 32%, as checked by the release of the Fmoc group from an aliquot. 

A variety of methods have been developed for the selective installation of chirality at oxindole C3 that involve transfer of functionality from indole C2. The Vedejs group has prepared a small collection of chiral DMAP (4-(lV,A-dimethylamino) pyridine) derivatives bearing conformationally restricted side chains that have been employed as nucleophilic catalysts to direct the transfer of indolyl C2 acetate or carboxylate groups to oxindole C3 with excellent enantiofacial selectivity [15]. As illustrated in Scheme 1, indolyl acetate 1 was converted to the chiral oxindole 3 (94%, 91% ee) using DMAP catalyst 2, while the opposite sense of enantioselec-tivity was observed when indolyl carboxylate 4 was treated with DMAP catalyst 5 to afford 6 as the major oxindole adduct (99%, 94% ee). In addition to probing modifications of the DMAP side chains, it was demonstrated that the overall rate of the reaction catalyzed by DMAP 2 was decreased when the indolyl acetate 1 contained a branched isopropyl substituent at C3 however, good enantioselectivity was observed with the branching substituent (82%, 94% ee). It was also... 

Moreover, in conjunction with readily available Mgl2 as a co-catalyst, Fu s planar chiral DMAP derivative 381 has been applied successfully to an MBH reaction involving the addition of cyclopentenone to aromatic and aliphatic aldehydes, affording the corresponding adduct in good to excellent yields with moderate to excellent enantiomeric excesses (Scheme 2.219). This work first suggests that the scope of reactions catalyzed by Fu s planar chiral DMAP catalysts can be increased by employing a simple co-catalyst. ... 

One of the typical applications of chiral DMAP catalysts is the atylative kinetic resolution of racemic secondary alcohols. Two landmark catalj ts, planer chiral DMAP catalyst 7 and chiral bicyclic PPY catalyst 10, were developed independently by Fu and Kawabata, respectively (Schemes 22.1 and 22.2). Catalysts 7 showed excellent properties as chiral nucleophilic catalysts. In the presence of 2 mol% of 7b, a variety of racemic secondaiy alcohols possessing aryl (or vinyl) and allg l groups such as 8 and 9 were kinetically resolved with acetic anhydride to give the acetates and the recovered starting materials in high enantioselectivity (s = 12-52) (Scheme 22.1). ... 

Scheme 22.1 Acylative kinetic resolution of racemic secondaiy alcohols with Fu s planar-chiral DMAP catalysts.

Kurahashi T, Mizutani T, Yoshida J-I (2002) Functionalized DMAP catalysts for regioselective acetylation of carbohydrates. Tetrahedron 58 8669... 

All of the above DMAP catalyst architectures rely upon the use of a chiral Lewis-base-mediated transformation to generate a reactive chiral acyl transfer species in situ. 

Recently, Vedejs found that a mixture of tributylphosphine and acetic anhydride acylates alcohols faster than acetic anhydride with DMAP. However, the combination of acetic anhydride with DMAP and triethylamine proved superior. It is believed that the EtsN prevents HOAc from destroying the DMAP catalyst. 

To substantiate the initiating species, reaction of excess benzyl alcohol with one equivalent of DMAP to lactide was investigated to generate a single turnover event. The lactide was ring opened with the formation of the benzyl ester, however due to the large excess of the benzyl alcohol and DMAP catalyst, transesterification with the diester product, afforded the monoester . Conversely, 5ec-phenethyl alcohol ring-opened lactide quantitatively to the diester product with no evidence of adverse side... 

Recently, Connell and coworker screened a series of chiral amine nucleophiles (90-95) for the asymmetric MBH reaction of aromatic and aliphatic aldehydes with cyclopentenone in the presence of Mgl2 (Scheme 31.29) [43], They identified Fu s planar chiral DMAP catalyst 91 as the most efficient catalyst for this asymmetric MBH reaction, affording the products 97 in good to excellent yields and moderate to excellent enantioselectivities. Both aromatic aldehydes and aliphatic aldehydes were suitable for this reaction. They also pointed out that Mgl2 as a co-catalyst could accelerate the reaction rate. 

Scheme 41.18 Carbety s helicenoidal DMAP catalyst for the KR of secondary aryl alkyl...

SCHEME 944 Cascade reaction combining a hydrogen-bonding donor and a DMAP catalyst. 

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