Phosphines phosphine-sulfonamide catalysts

Metathetic ring closure. Catalyst 1. can be regarded as the standard workhorse for RCM and the scope of its applications continues to expand. Thus, its use in the elaboration of cyclic structures including azaspirocycles," 3-pyrrolines," and those containing phosphine oxides, phosphinates, dioxasilanes, - sulfonamides. l-(Dialkoxyboryl)vinylcycloalkenes are obtained from x-alken-l-ynyl boronates. ... 

The Sharpless ligand (DHQD>2AQN 45 was introduced to the asymmetric BH reaction in combination with acetic acid as co-catalyst. The ammonium salt generated in situ was proposed as a bifunctional catalyst, where the protonated amine acted as Brpnsted acid and the nonprotonated one performed as nucleophilic catalyst [99]. Besides, a simple phosphine-sulfonamide 46, synthesized readily from L-threonine, was found to be an efficient catalyst for the reaction of 7V-sulfonyl imines and (3-naphthyl acrylate to give the product in excellent enantioselectivities [100]. 

A series of bifunctional phosphine-sulfonamides have been developed as catalysts for the aza-MBH reactions. The threonine-derived candidate (200) turned out to be the most efficient (<97% ee) ... 

The L-threonine-derived phosphine-sulfonamide (23) is one of the best catalysts for the enantioselective aza-Morita-Baylis-Hillman reaction. A DPT study has identified ( ) a key intramolecular N-H—O hydrogen-bonding interaction between the sulfonamide... 

Figure 31.3 Novel bifunctional phosphine-sulfonamide organic catalysts 143-148 derived from natural amino acids.

The enantioselective hydroaminations of allenes with chiral phosphine catalysts was accomplished with substrates that had a terminal symmetric substitution and with the amines protected as carbamates or sulfonamides. The same symmetric substituents were necessary for the enantioselective transformation nsing chiral counterions. However, very recently, high enantiomeric excesses were reached with trisubstituted asymmetric allenes by a dynamic kinetic enantioselective hydroamination of allenyl carbamates (eqnation 110), even thongh the E/Z ratio of the prodncts was not optimal. 

Hydroamination of olefins is also possible with gold catalysts. In this reaction, the attack comes Ifom a nitrogen nucleophile as a carbamate,a urea, an amide, or a sulfonamide. In the latter case, the reaction can be carried out intermolecularly. While the carbamates, ureas, and amides give only products of intramolecular anunations, the sulfonamides can perform the intermolecular addition. Only the addition of ureas (equation 146) takes place at room temperature, and in the rest of the additions heating is required. The catalysts of choice in all these reactions are cationic gold(I)-species stabilized by phosphines or NHC ligands. The reaction times have been reduced by the use of microwave irradiation. The mechanism of the hydroamination reaction has been studied in detail theoretically. ... 

For example, reaction of methoxyallene with an allyHc alcohol under palladium catalysis yielded unsymmetrical mixed acetal 22a in 74% yield (Scheme 5(a)). Treatment of 22a with 10 mol% of Grubbs second generation catalyst 3, followed by add promoted aromatization yielded fiiran 12a in 79% isolated yield for the one-pot protocol. However, the nonpolar furan products were usually contaminated with (nonpolar) phosphine residues from the catalyst, which made the purification step problematic. Therefore, it was generally advantageous to purify the dihydrofuran intermediate prior to the aromatization step. In a similar manner to furans, allyftc sulfonamide 21a was converted to the N,0-acetal 23a in 63% yield under palladium catalysis. Then RCM followed by aromatization proceeded smoothly to provide the desired N-protected pyrrole 13a in 61% yield over two steps (Scheme 5(b)). This procedure can also be applied... 

The success of simple Au(I) PPhj systems for catalysis inspired the development of less strongly donating phosphine hgands in order to enhance it-acidity to improve reactivity with protected amines. Using triphenyl phosphite as a hgand, intermolecular hydroamination of alkenes with sulfonamides can be accomphshed with low catalyst loadings (Scheme 15.63) [263]. 

Rhodium catalysts have been widely used for C-C bond formation processes [71], Particularly noteworthy are the Rh(I)-catalyzed additions of boronic acids and their derivatives to a.p-unsaturated carbonyl compounds [72-78] and aldehydes [75, 79] (Chapter 4). The groups of Miyaura and Hayashi have shown that Rh(I) catalyzes the addition of sodium tetraphenylborate and arylstannanes to N-sulfonylimines [80-82]. Miyaura and co-workers have also reported the first example of a Rh(I)-cat-alyzed addition of an arylboronic acid to an N-sulfonylimine (77), to give sulfonamide 78 (Equation 13) [83]. Reactions proceeded with 2 equivalents of arylboronic acids using either a cationic Rh(I) catalyst alone, or in combination with appropriate phosphine ligands such as bis(diphenylphosphino)propane or P(i-Pr)3. Boronic esters will also react, particularly in the presence of triethylamine. The reaction does not proceed with simple aldimines, such as PhCH NPh. 

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