Bis-sulfonamide complexes

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... 

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). 

The enantioselective amination of iV-acyl oxazolidinones has been studied as part of a general approach to the synthesis of arylglycines. In this case, the enolization is initiated by a chiral magnesium bis(sulfonamide) complex. The oxazolidinone imide enolates are generated using catalytic conditions (10 mol% of magnesium complex) and treated in situ with BocN=NBoc to provide the corresponding hydrazide. 20 mol% of iV-methyl-p-toluensulfonamide are added to accelerate the reaction (equation 117). 

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). 

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. 

A variety of bis(sulfonamide) complexes of the form TiX2(C6H10(NSO2R)2),857-861 TiX2(PhCH(NS02R))2, and Ti((PhCH(NS02R)2))2862 have been prepared. A number of these complexes have been structurally characterized. In addition, these and related compounds have been used as catalysts for enantioselective addition of alkyl groups to aldehydes. 

S.2. Bis-Sulfonamide Complexes (Written vnth Prof. Patrick J. Walsh)... 

The existence of ketenes was established over a hundred years ago, and, in recent years, asymmetric synthesis based on [2 + 2] cycloadditions of ketenes with carbonyl compounds to form chiral p-lactones has been achieved with high yields and high stereoselectivities. In 1994, Miyano et al. reported the use of Ca-symmetric bis(sulfonamides) as ligands of trialkylaluminum complexes to promote the asymmetric [2 + 2] cycloaddition of ketenes with aldehydes. The corresponding oxetanones were obtained in good yields and enantioselectivities... 

The metallation should proceed via the formation of a chelated tetrahedral magnesium enolate complex, with a (Z)-geometry. The conformational rigidity would be enforced by chelation of both the imide enolate and bis(sulfonamide) ligand to the tetrahedral magnesium ion. 

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. 

Catalytic asymmetric vinylation of ketones has been achieved. Vinylzinc reagents have been generated by hydrozirconation of terminal alkynes which are then transmet- allated with zinc.199 A titanium(IV) complex of a tims-cyclohexane-bis(sulfonamide) provides chiral catalysis it also facilitates dienylation of ketones, with ees also >90% in this case. 

Sun s group reported the synthesis, characterization, and photophysical properties of a series of organic receptors and their corresponding Re(I) tricarbonyl complexes as anion probes, featuring bis-sulfonamide as interacting sites attached to highly chromophoric Ji-conjugated quinoxaline moieties (see Fig. 18) [155],... 

In 1992 Kobayashi et al. [47] reported the first catalytic and enantioselective cyclo-propanation using the Furukawa modification [48] of the Simmons-Smith reaction of allylic alcohols in the presence of a chiral bis(sulfonamide)-Zn complex, prepared in-situ from the bis(sulfonamide) 63 and diethylzinc. When cinnamyl alcohol 62 was treated with EtgZn (2 equiv.), CHgIg (3 equiv.), and the bis(sulfonamide) 63 (12 mol %) in dichloromethane at -23 °C, the corresponding cyclopropane 64 was obtained in 82 % yield with 76 % ee (Sch. 26). They proposed a transition state XXIII (Fig. 5) in which the chiral zinc complex interacts with the oxygen atom of the allylic alkoxide and the iodine atom of iodomethylzinc moiety. They also reported the use of the bis(sulfonamide)-alkylaluminum complex 65 as the Lewis acidic component catalyzing the Simmons-Smith reaction [49]. 

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]. 

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 A, A -bis(arenesulfonyl)cyclohexane-1,2-diamines used as chiral controllers (see also Houben-Weyl, Vol. E21, pp 1327, 3895) can also be employed as their aluminum complexes to catalyze the cyclopropanation of allylic alcohols with diethylzinc and diiodomethane. ° The bis(sulfonamide)aluminum complex was first prepared in situ in 1,2-dichloroethane and after removal of the solvent in vacuo, cyclopropanation was carried out in dichloromethane at — 20 °C. The enantioselectivities are similar to those obtained with the chiral zinc catalyst described above. However, the most characteristic feature of the chiral aluminum complex catalyzed reaction is that no decrease in the enantioselectivity was observed even at a higher concentration. An electron-withdrawing group on the benzene ring of the sulfonamide or the... 

The cycloaddition of functionalized cyclopentadiene and dienophile 83 was better performed by use of an entirely different, non-phenoxide-type aluminum complex (Scheme 6.53). Thus a chiral catalyst endowed with the more electron-with-drawing bis (sulfonamide) ligand was explored by Corey and coworkers [73]. The reaction of the trons-crotyl derivative 83 and cyclopentadiene with 20 mol% 84 as catalyst at -78 °C for 16 h provided adduct 85 in 88% yield and 94% ee. The ad-... 

Doye s group [81] showed that a dinuclear titanium-sulfonamidate complex (Scheme 21), with a tetrahedral sulfur in the ligand backbone, can be used for intermo-lecular hydroaminoalkylation as well. This system gives mixtures of branched and linear products, although to date there has been no mechanistic rationale provided for the reduced regioselectivity of group 4 metal complexes in this transformation. There has been one report by Zi s group [44] that describes axially chiral bis(sulfonamidate) tantalum and niobium complexes for application as precatalysts for hydroamination and hydroaminoalkylation. Unfortunately, these complexes did not show any reactivity for either of these reactions. 

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