Hiroya Takada

Amination of ethers using chloramine-T hydrate and a copper(I) catalyst

Amination of C-H bonds activated by ether oxygen atoms is facile with chloramine-T as nitrene source and copper(I) chloride in acetonitrile as catalyst. For cyclic ethers the hemiaminal products are generally stable and can be isolated pure. For acyclic ethers, the hemiaminal products, as expected, fragment with elimination of alcohol to yield imines. When activation of benzylic positions is remote through a conjugated system, stable benzylamine derivatives are isolated. Mechanistic studies are consistent with concerted insertion of an electrophilic nitrenoid into the C-H bond in the rate-determining step, though in an asynchronous manner with a more activated substrate.

Catalytic Diastereoselective Imidation of Diaryl Sulfides Bearing a Chiral Oxazolinyl Moiety with Chloramine T Trihydrate

Up to 99 % de is obtained in the imidation of diaryl sulfides bearing a chiral oxazolinyl moiety at the ortho position. The corresponding N-p-tosylsulfimides are produced upon use of chloramine T trihydrate in the presence of Cu(OTf)2 as catalyst [Eq. (1)]. OTf=trifluoromethanesulfonate; Ts=toluenesulfonyl.

Asymmetric imidation of organic selenides into selenimides

Abstract Treatment of aryl benzyl selenides with [N-(p-toluenesulfonyl)imino]phenyliodinane [TsNIPh] in the absence or presence of copper(I) salt in toluene or acetonitrile affords the corresponding N-tosylselenimides in 31–46% yield. When the reaction is carried out in the presence of optically active 4,4′-disubstituted bis(oxazoline) as a ligand together with molecular sieves, enantioselective imidation occurs to give optically active N-tosylselenimides and the best result is obtained from benzyl 2-naphthyl selenide (64% yield and 36% ee). Similar treatment of allylic selenides gives the corresponding optically active allylic amides (up to 71% yield and 30% ee). In the case of diastereoselective imidation, the reaction of diaryl selenides bearing a chiral oxazolinyl moiety with TsNIPh or Chloramine–T trihydrate [TsN(Cl)Na·3H2O] has been successfully carried out to give the corresponding optically active N-tosylselenimides in good yields (up to 97% isolated yield and 76% de). The absolute configuration around the selenium atom of (4S)-Se-[2-(4-isopropyloxazolin-2-yl)phenyl]-Se-phenyl-N-(p-toluenesulfonyl)selenimide [(4S)-13], obtained by diastereoselective imidation of the corresponding selenide with Chloramine–T trihydrate, has been determined to be S by X-ray crystallographic analysis, from the result of which an ionic reaction pathway involving a chloroselenonium ion intermediate is proposed.

Catalytic diastereoselective sulfimidation of diaryl sulfides and application of chiral sulfimides to asymmetric allylic alkylation

The copper-catalyzed diastereoselective imidation of diaryl sulfides bearing a chiral oxazolinyl moiety at the ortho-position with [N-(p-toluenesulfonyl) imino]phenyliodinane (TsN=IPh) or Chloramine-T trihydrate [TsN(Cl)Na.3H2O] was successfully carried out to give the corresponding optically active N-tosylsulfimides in good yields. For example, the imidation of diphenyl sulfide bearing a methoxymethyl moiety at the 4-position of the oxazoline ring with TsN(Cl)Na.3H2O in acetonitrile in the presence of 10 mol% Cu(OTf)2 at 25 degrees C for 24 h affords the corresponding optically active N-tosylsulfimide in 52% isolated yield with a high diastereoselectivity of 99%. Hydrolysis of the optically active N-p-tosylsulfimides converts them into the corresponding optically active sulfimides in high yields without loss of diastereoselectivity. These novel optically active sulfimides and N-tosylsulfimides work as efficient chiral ligands for palladium(II)-catalyzed allylic alkylation of 1, 3-diphenyl-3-acetoxy-1-propene with dimethyl malonate to give the corresponding alkylation product quantitatively and with a high stereoselectivity (up to 90% ee).

Chalcogen Chiral Ylides for the Catalytic Asymmetric Epoxidation of Aldehydes: From Sulfur to Selenium and Tellurium

Abstract The reaction of novel chiral selenonium and telluronium ylides was investigated with aldehydes and compared to the sulfur analogues. (2R,5R)-2,5-Dimethylselenolane was prepared and reacted as a catalyst for the benzylidenation of aldehydes. Disubstituted epoxides were readily prepared with a (surprising) absence of diastereoselectivity, and with enantiomeric excesses higher than 90%. The reaction of a tellurium analogue, (2S,5S)-2,5-diethyltellurolane, afforded the oxirane in very moderate yield and e.e.s in the range of 62–82%. Though this was less productive, it is the first report of a chiral telluronium ylide leading to an asymmetric epoxidation of aldehydes.

4-Penteneselenothioic acid S-alkyl esters: Synthesis via the seleno-Claisen rearrangement

Abstract Selenothioic acid S -alkyl esters were reacted with allylic bromides in the presence of Et 3 N. Mono-, di- or tri-allylatd products were selectively formed by changing reaction temperatures, times and allylic bromides used. The reaction proceeded with high regio- and stereoselectivity via the seleno-Claisen rearrangement. The selective synthesis of monoallylated esters was also attained by the reaction of in-situ generated lithium eneselenolates with allylic bromides.

Catalytic asymmetric imidation of selenides into selenimides

The direct catalytic imidation of various prochiral selenides with TsNIPh in the presence of CuOTf using chiral 4,4′-disubstituted 2,2′-bis(oxazoline) ligand afforded the corresponding chiral selenimides (∼36% ee).

Reaction of selenothioic acid S-alkyl esters with electron deficient alkynes: Selective synthesis of cyclic selenides and acyclic divinyl selenides

Abstract The reaction of selenothioic acid S -alkyl esters with electron deficient alkynes was carried out under reflux in toluene to give cyclic selenides in good yields. On the contrary, the similar reaction in MeOH or CH 2 Cl 2 with Et 3 N afforded acyclic divinyl selenides in good to high yields.

Iridium(I)-catalysed asymmetric hydrosilylation of ketones using a chiral oxazolylferrocene-phosphine hybrid ligand

The chiral oxazolylferrocene-phosphine hybrid ligand(DIPOF) is a very effective ligand for IrI-catalysed asymmetric hydrosilylation of simple ketones to give the corresponding sec-alcohols(up to 96% ee) after acid hydrolysis.

Novel asymmetric catalytic synthesis of sulfimides

Prochiral sulfides react with PhINTs in the presence of a catalytic amount of CuI salt together with chiral 4,4′-disubstituted bis(oxazoline) ligands to afford the corresponding chiral sulfimides.