Oxazoline ligands sulfide-oxazolines

Aromatic and vinylic sulfides take part in cross-coupling reactions with Grignard reagents in the presence of Ni catalysts.336,337 This reaction has been applied to the enantioselective synthesis of binaphthyls using a standard chiral oxazoline ligand (Equation (25)) 338... 

The readily available oxazolines (L19) are used in the cross-coupling of arylboronic acids with aryl bromides, including nonactivated ones in the system (Pd(OAc)2/L, Cs2C03, dioxane, 80 °C). It is notable that the system works well at 1 1 Pd L ratio.442 A simple sulfide complex showed similar activity (PdCl2(SEt2)2, K3P04, DMF, 130°C).18 A series of bidentate N,N-donor ligands... 

The 1-t-butylphospholane sulfide intermediate to TangPhos was also used to prepare the P,N ligands 48 by reacting the lithium complex with C02 and then oxazoline formation with a range of chiral amino alcohols [69b, 74]. The Ir complexes of these ligands have been successfully used in the reduction of / -methylcinnamic esters (80-99% ee) and methylstilbene derivatives (75-95% ee), a particularly challenging class of unfunctionalized olefins [4 c]. 

Uemura and co-workers discovered that prochiral sulfides react with [N-(p-toluenesulfonyl)imino]phenyliodinane 207 in the presence of bis(oxazoline) ligands to form the corresponding chiral sulfimides. ° For example, ( )-cinnamyl phenyl sulfide 220 reacted with 207 in the presence of copper(I) triflate and ent-6 to form the chiral sulfimide 221 in 80% yield (58% ee) as shown in Figure 9.63. 

Organometallic compounds asymmetric catalysis, 11, 255 chiral auxiliaries, 266 enantioselectivity, 255 see also specific compounds Organozinc chemistry, 260 amino alcohols, 261, 355 chirality amplification, 273 efficiency origins, 273 ligand acceleration, 260 molecular structures, 276 reaction mechanism, 269 transition state models, 264 turnover-limiting step, 271 Orthohydroxylation, naphthol, 230 Osmium, olefin dihydroxylation, 150 Oxametallacycle intermediates, 150, 152 Oxazaborolidines, 134 Oxazoline, 356 Oxidation amines, 155 olefins, 137, 150 reduction, 5 sulfides, 155 Oxidative addition, 5 amine isomerization, 111 hydrogen molecule, 16 Oxidative dimerization, chiral phenols, 287 Oximes, borane reduction, 135 Oxindole alkylation, 338 Oxiranes, enantioselective synthesis, 137, 289, 326, 333, 349, 361 Oxonium polymerization, 332 Oxo process, 162 Oxovanadium complexes, 220 Oxygenation, C—H bonds, 149... 

The treatment of various sulfides with Phi = NTs in the presence of cuprous triflate leads to the corresponding N-tosylsulfimides (N-tosylsulfilimines) 21 [30]. The presence of the chiral bis(oxazoline) ligand 22 in the reaction medium results in coordination of the copper(III)-nitrene intermediate, L Cu(III) = NTs, and enables the enantioselective production of 21 (Scheme 12). Similar copper-catalyzed reactions of allylic sulfides with Phi = NTs lead to formal insertion of the NTs group into the carbon-sulfur bond of the substrates, and proceed via a [2,3]-rearrangement with allylic inversion, to give sulfonamides 23 [30]. 

Organocopper reagents are the most reliable species for conjugate additions and a number of approaches towards chiral cuprates has been developed. The approaches are classified into two categories one is the chiral heterocuprate obtained by treatment with chiral alcohols, amines, sulfonamides, and thiols. The other involves organocopper compounds coordinated by chiral external ligands such as phosphines, sulfides, and oxazolines. 

The enantioselective C-silylation of allylic substrates such as (V-(terf-butoxycarbonyl)-A(-(p-methoxyphenyl)allylamines or 1,3-diphenylpropene is accomplished with butyUithium in the presence of (—)-sparteine, followed by the addition of TMSOTf (eq 47). The same procedure allows the asymmetric deprotonation-substitution of arenetricarbonyl(O) complexes, while chiral bis(oxazolines) have been the ligands of choice to perform such transformation with aryl benzyl sulfides in these reactions, different yields and enantioselectivities are reached if trimethylsilyl chloride is used as sUylating reagent, although there is a substrate dependence and no definite rules can be established. 

The enantioselective deprotonation of 128 and oxidative addition of the carbanion with Cu(II) afforded TangPhos disulfide as a mixture of diaster-eomers where the chiral C2-symmetric product was the major compound (66% de, 95% ee). A single recrystallisation afforded the desired optically pure TangPhos sulfide in 20% yield. The desulfuration was performed with hexa-chlorodisilane to yield the very air-sensitive Tangphos diphosphine in 88% yield. The synthesis of a family of phospholane-oxazoline ligands started with the preparation of carboxylic acid 129 by the proeedure in 40% yield after recrystallisation. The crude product was obtained in relatively low optical... 

Methylation by MeOTf can also be carried out asymmetrically. Treatment of a-lithio benzyl 2-quinolyl sulfide with MeOTf in the presence of a bis(oxazoline) as an external chiral ligand yielded chiral 1-phenylethanethio quinolyl sulfide (eq 17). Lithiation adjacent to nitrogen of chiral 3,4-substituted piperidines and pyrrolidines followed by diastereoselective substitution with MeOTf offered general routes to 2,4,5- and 2,4,5,6-substituted piperidines as well as 2,3,4- and 2,3,4,5-substituted pyrrolidines. ... 

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