Bis-sulfonamide catalyst

Jorgensen and co-workers employed chiral bis-sulfonamide catalyst 27, a proven ligand for metal-based asymmetric catalysis, for the Friedel-Crafts alkylations of N-methylindoles (24) using -substituted nitroolefins [52]. Using optimized conditions, 2 mol% 27 gave the desired indole alkylation products of substituted aryl and heteroaryl nitroolefins in moderate to high yields (20-91%) and moderate enantiopurities (13-63% ee Scheme 6.3). Aliphatic -substitution... 

Jorgensen and co-workers reported the asymmetric additions of a silyl ketene acetal to aldehydes (40) using the chiral bis-sulfonamide catalyst 27 [109]. Among the limited number of aldehydes examined, adducts were obtained in moderate to high yields (41-90%) and modest levels of ee (30-56% Table 6.44). The corresponding mono-sulfonamide catalyst was inactive under the reported conditions. 

This method is comparable to similar, catalytic Sim-mons-Smith-type methods employing the titanium TADDOL catalyst 20 (95 5 er) or the Ci-symmetric bis-sulfonamide catalyst 32 (93 7 er) for the cyclopropanation of the allylic alcohol 22 (eq 6). However, due to the preliminary nature of these earlier investigations, substrate scope and generality have not been extensively documented. All of the aforementioned methods are limited by their dependence on the allylic alcohol functionality. Only one method for Simmons-Smith-type cyclopropanation of other substrate classes has been developed. Use of a stoichiometric, chiral dioxaborolane [CAS 161344-85-0] additive allows for selective cyclopropanation of allylic ethers, homo-ally lie alcohols and allylic carbamates. ... 

The scope of the reaction was examined with a catalyst prepared from the benzene sulfonamide and DIBAL, because it was found that essentially the same induction could be obtained as with those obtained from tri-/so-butyl aluminum. Two years earlier the authors had reported that this Simmons-Smith reaction could also be catalyzed by the aluminum-free sulfonamide 132 (optimum with Ar = /7-NO2C6H4) the induction obtained is listed in the far right column of Table 8 [34]. It was proposed that a zinc complex of 132 is generated in-situ. Surprisingly, with the exception of the silyl-substituted allyl alcohol (the last entry in the table) [35], almost identical asymmetric induction obtained by use of the aluminum-containing and aluminum-free catalysts. The main advantage of the diazaaluminolidine catalyst is that it is apparently more soluble than the aluminum-free bis-sulfonamide catalyst, with the result that a tenfold increase in concentration (0.1 m) can be used this might explain the increased rate observed for the diazaaluminolidine catalyst. Finally, it has recently been reported that a catalyst formed from the Ci symmetrical sulfonamide 135 and DIBAL will induce the formation of 131 from cinnamyl alcohol in 68 % ee [36]. 

A chiral bis-sulfonamide catalyst (35) was developed by Tonoi and Mikami and glyoxylates underwent hetero Diels-Alder reaction of Danishefsky s diene to give cyclohexenone derivatives with high ees (Scheme 2.78) [146]. 

In 2005, Jorgensen and Mikami independently reported the hetero-Diels-Alder reachon of Danishefsky s diene 114 with glyoxylates or glyoxals 118 using a class of chiral bis-sulfonamides catalyst 119a,b derived from 1,2-diphenyl-l,2-diamine... 

Chiral boron(III) complexes can catalyze the cycloaddition reaction of glyoxy-lates with Danishefsky s diene (Scheme 4.18) [27]. Two classes of chiral boron catalyst were tested, the / -amino alcohol-derived complex 18 and bis-sulfonamide complexes. The former catalyst gave the best results for the reaction of methyl glyoxylate 4b with diene 2a the cycloaddition product 6b was isolated in 69% yield and 94% ee, while the chiral bis-sulfonamide boron complex resulted in only... 

In 2005, a novel C2-symmetric bis(sulfonamides) ligand was easily prepared in three steps by Wang et al. and further applied to the enantioselective addition of alkynylzine reagents to aldehydes performed in the presence of Ti(Oi-Pr)4. When a catalyst loading of 4 mol% was used, a high enantioselectivity of up to 97% ee was achieved, as shown in Scheme 3.65. When the amount of the... 

The concept of chiral magnesium amides for the preparation of magnesium enolates has been extended to chiral magnesium bis(sulfonamide) complexes as catalysts for the enolization of A-acyloxazolidines ° (equation 63). 

On the other hand, in the presence of Lewis acid, addition of dialkylzinc to ketones occurs (equation 14)45. A stoichiometric amount of Ti(OPr-i)4 and a catalytic amount of camphorsulfonamide 33 enable an enantioselective addition of dialkylzincs to ketones46. Later, bis(sulfonamide) ligand 34 was found to be a more enantioselective catalyst in this... 

In early studies of these reactions, the turnover efficiency was not always high, and stoichiometric amounts of the promoters were often necessary to obtain reasonable chemical yields (Scheme 105) (256). This problem was first solved by using chiral alkoxy Ti(IV) complexes and molecular sieves 4A for reaction between the structurally elaborated a,/3-unsaturated acid derivatives and 1,3-dienes (257). Use of alkylated benzenes as solvents might be helpiul. The A1 complex formed from tri-methylaluminum and a C2 chiral 1,2-bis-sulfonamide has proven to be an extremely efficient catalyst for this type of reaction (258). This cycloaddition is useful for preparing optically active prostaglandin intermediates. Cationic bis(oxazoline)-Fe(III) catalysts that form octahedral chelate complexes with dienophiles promote enantioselective reaction with cyclopentadiene (259). The Mg complexes are equally effective. 

Chiral bis-sulfonamides have been employed as catalysts of enantioselective addition of a range of organozincs to simple aryl ketones, in ees up to 99%, using Ti(IV) tetraisopropoxide methodology.237... 

A range of asymmetric alkyl additions to ketones have been carried out using highly concentrated or solvent-free conditions to produce greener conversion 292 The loading of catalyst - a bis-sulfonamide - can be significantly decreased under these conditions. 

Nitroalkenes react enantioselectively (ee usually 40%) with indoles using chiral hydrogen-bonding bis-sulfonamides as catalysts [e.g. to form (41)].44 An enantioselective reaction (usually ee 83-95%) has been shown to occur between indoles and ethyl ... 

The use of bis(sulfonamide) ligands derived from stilbenediamine in the asymmetric addition of diethylzinc to benzaldehyde has resulted in large changes in product ee over the course of the reaction.106 This effect has been attributed to autoinduction. During the reaction the catalyst evolves by incorporation of the product of the asymmetric addition reaction. 

Chiral bis-sulfonamides 162-163 are a new group of organo catalysts for the enantioselective Friedel-Crafts alkylation of indoles to nitroolefins. The hy-... 

A catalytic approach to the synthesis of arylglycines was proposed by Evans and coworkers using enantioselective amination of iV-acy 1 oxazolidinones [54], Metallo-bis(sulfonamide) complexes derived from chiral diamines are potential chiral catalysts. The magnesium-bis(sulfonamide) complex 109 was generated by treating (S,S)-bis(sulfonamide) 108 with dimethylmagnesium in dichloromethane (Scheme 50). 

Additions to Aldehydes. Alkylation of aromatic and aliphatic aldehydes with a combination of titanium tetraisopropoxide, Ti(0-/-Pr)4, and diethy Izinc, ZnEt2, in the presence of a catalytic amount of the bis-sulfonamide la leads to formation of (S)-l-phenyl-1-propanol 4 with high enantioselectivity (eq 2, Table 1). Use of the (R,7 )-l,2-(trifluoromethanesulfonamido)-cyclohexane lb [CAS 122833-60-7] allows for an equally selective reaction, but at exceptionally low catalyst loadings. In the case of aromatic aldehydes, these reactions are fairly rapid, requiring at most 2 hours to reach full conversion. 

The role of Z11I2 is that an equimolar quantity of the compound drives the Schlenk equilibrium from the reagent bis(iodomethyl)zinc to (iodomethyl)zinc iodide, which is the actual cyclopropanation catalyst and has high reactivity and stereoselectivity [50c,52], The structure of the active catalyst, Zn-bis(sulfonamide) complex XXIV, was characterized by NMR analysis and X-ray study of the structure of its bipyri-dyl complex 66 (Sch. 28) [53]. The Zn-bis(sulfonamide) complex XXIV aggregates in solution and functions as a divalent Lewis acid. 

The BINOL-aluminum catalyst 121 could only successfully be used in stoichiometric amounts this limitation was overcome by the same research group in the same year with the introduction of the diazaaluminolidine catalysts 124 (Table 6) [29]. These catalysts are prepared from the bis-sulfonamide 123 and the structure of 124 has been confirmed by X-ray diffraction [30]. The reaction of a variety of aldehydes with catalyst 124c was examined and it was observed that with the exception of ben-zaldehyde, higher asymmetric induction was associated with increased aldehyde size. Unlike catalyst 121, catalyst 124c gives the same sense of facial selectivity with both aliphatic and aromatic aldehydes. The enantioselectivity of catalyst 124c was also slightly dependent on the nature of the alkyl aluminum used in the preparation of the... 

The number of chiral diazaaluminolidine catalysts has been extended by Dymock, Kocienski and Pons, who introduced the more convenient to handle trimethylsilyl-ketene [31]. The catalysts in this study were prepared from slightly different sulfonamides but asymmetric induction was comparable with that obtained with the ketene and similar aldehydes. With trimethylsilylketene, two diastereomers are possible and in all examples studied the cis isomer 126 was the predominate product. TTie reactions in Table 7 were performed with 30 mol % catalyst—with 20 mol % catalyst the reaction is incomplete. A more active catalyst can be prepared from the bis-trifluoro-methylsulfonyl derivative of 128, but asymmetric induction was low. It was reported that ortho substituents on the aryl sulfonamide were necessary for higher induction but data were provided only for the aryl sulfonamide substituents summarized in Table 7. Both symmetrical and unsymmetrical diazaaluminolidines were examined as catalysts in an attempt to optimize asymmetric induction but significant differences were not found. The catalyst prepared from the symmetric bis-sulfonamide 128 with Ar = 2,4,6-tri-/yo-propylphenyl did not give any reaction even at 100 mol %. 

The first asymmetric Simmons-Smith reaction with a chiral Lewis acid catalyst was introduced in 1994 by Charette and Juteau and featured a chiral boron Lewis acid prepared from tartaric acid [32]. Although this process resulted in excellent enantioselec-tivity, it would not turnover, i.e. the yield was less than 10 %. In the same year Imai, Takahashi and Kobayashi introduced a chiral aluminum Lewis acid that would catalyze the cyclopropanation of allylic aleohols with significant turnover numbers but their system did not lead to asymmetric induction as high as that resulting from the dioxaborolane catalyst [33]. The catalyst is prepared from the bis-sulfonamide 132... 

An effective chiral aluminum catalyst prepared from the bis-sulfonamide 263 was reported by Corey, Imwinkelried, Ikul, and Xiang for the Diels-Alder reaction of N-acyloxazolidinones [55]. They found that 10 mol % catalyst 266 would effect the reaction of A-acrylyl derivative 261 in 10 min at -78 °C to give the endo adduct 262 in 92 % yield and 91 % ee. The reaction of the N-crotyl derivative 197 was slower but... 

A more extensive study was conducted with methallyltributylstannane the results are shown in Sch. 43. Here the promise shown by the catalyst prepared from the bis-sulfonamide was not fulfilled. This screening involved all the ligands shown in Sch. 42 and reaction temperatures of 10 and -78 °C. Here both the BINOL and bis-sulfon-amide ligands were found to be ineffectual and the best ligand was TADDOL with 1-naphthyl substituents, although poor induction was achieved with the catalyst prepared from this ligand. 

The formation of a quaternary carbon center by the radical-mediated allylation of an a-iodolactone was examined for substrate 341 by Murakata, Jono, and Hos-hino [71]. Lewis acids for this reaction were prepared from a bis-sulfonamide and tri-methylaluminum in dichloromethane. Other aluminum compounds were employed in the preparation of the catalyst but all resulted in similar or lower asymmetric induction. The Lewis acid was complexed with the lactone and then the allylation procedure in Sch. 44 was performed. It was found that superior asymmetric induction could be achieved if the Lewis acid was prepared from the ligand with two equivalents of trimethylaluminum. It was also interesting that some turnover could be achieved, as indicated by the data obtained from use of 50 mol % catalyst. 

The same reaction was investigated with the substituted BINOL catalyst 98 and initially it was found to be inferior to catalysts prepared from the bis-sulfonamides. Surprisingly, it was found that in the presence of 1 equiv. diethyl ether high asymmetric induction could be achieved as summarized in Table 17 [72]. The reactions are also greatly accelerated by the presence of ether. It was suggested that a pentacoordi-nate aluminum species is involved in this reaction. The effect of ether was observed for all reactions whether or not an ether linkage was present in the substrate. The effect falls off with more hindered ethers and with amines. Another remarkable aspect of this reaction is that the catalyst to substrate ratio can be reduced to 10 mol % although the induction does fall off to some extent. 

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