Design of new chiral phase-transfer catalysts with dual functions for highly enantioselective epoxidation of alpha,beta-unsaturated ketones.

A new chiral ammonium bromide, 1-Br, possessing diarylmethanol functionality as a substrate recognition site has been designed as a promising, dual-functioning catalyst for the highly enantioselective epoxidation of alpha,beta-unsaturated ketones under mild phase-transfer conditions. For instance, vigorous stirring of a mixture of chalcone, 1-Br (3 mol %), and 13% NaOCl in toluene at 0 degrees C for 24 h gave rise to epoxy chalcone quantitatively with 96% ee. A variety of alpha,beta-unsaturated ketones can also be epoxidized with rigorous stereochemical control, clearly demonstrating the effectiveness and utility of the present system.

Development of a recyclable fluorous chiral phase-transfer catalyst: application to the catalytic asymmetric synthesis of alpha-amino acids.

[structure: see text] A recyclable fluorous chiral phase-transfer catalyst was synthesized and successfully applied for the catalytic asymmetric synthesis of both natural and unnatural alpha-amino acids. The reaction involves alkylation of a glycine derivative followed by extractive recovery of the chiral phase-transfer catalyst using fluorous solvent.

Stereoselective terminal functionalization of small peptides for catalytic asymmetric synthesis of unnatural peptides.

The asymmetric phase-transfer catalytic alkylation of peptides has been achieved by the use of designed C(2)-symmetric chiral quaternary ammonium bromide 1 as catalyst. Excellent stereoselectivities were uniformly observed in the alkylation with a variety of alkyl halides and the efficiency of the transmission of stereochemical information was not affected by the side-chain structure of the preexisting amino acid residues. This method also enables an asymmetric construction of noncoded alpha,alpha-dialkyl-alpha-amino acid residues at the peptide terminal.

(2,7-Disubstituted-1,8-biphenylenedioxy)bis(dimethylaluminum) as bidentate organoaluminum Lewis acids: elucidation and synthetic Utility of the double electrophilic activation phenomenon.

A series of (2,7-disubstituted-1,8-biphenylenedioxy)bis(dimethylaluminum) (2) has been readily prepared in situ by treatment of the requisite 2,7-disubstituted-1,8-biphenylenediol (1) with Me3Al (2 equiv) in CH2Cl2 at room temperature; this primarily relies on the successful establishment of a new synthetic procedure of 1 starting from inexpensive m-anisidine. Evaluation of 2 as a bidentate organoaluminum Lewis acid has been performed by the reduction of ketonic substrates using Bu3SnH as a hydride source in comparison to the conventional monodentate Lewis acid dimethylaluminum 2,6-xylenoxide (11), uncovering the significantly high activation ability of 2 toward carbonyl. Particularly, (2,7-dimethyl-1,8-biphenylenedioxy)bis(dimethylaluminum) (2a) exerted the highest reactivity, which has also been emphasized in the Mukaiyama aldol reaction.

Catalytic asymmetric allylation of aldehydes and related reactions with bis(((S)-binaphthoxy)(isopropoxy)titanium) oxide as a mu-oxo-type chiral Lewis acid.

A new, chiral bis-Ti(IV) oxide of type 3 has been designed and can be utilized for strong activation of aldehyde carbonyls, thereby allowing a new catalytic enantioselective allylation of aldehydes with allyltributyltin. The chiral bis-Ti(IV) catalyst (S,S)-3 can be readily prepared either by treatment of bis(triisopropoxy)titanium oxide with (S)-BINOL or by treatment of ((S)-binaphthoxy)isopropoxytitanium chloride with silver(I) oxide. Treatment of hydrocinnamaldehyde with allyltributyltin under the influence of chiral bis-Ti(IV) oxide (S,S)-3 generated in situ (10 mol %) in CH(2)Cl(2) afforded an allylation product in 84 % yield and with 99 % ee.

Fluorotetraphenylbismuth: a new reagent for efficient regioselective alpha-phenylation of carbonyl compounds.

Synthesis and X-ray crystallographic characterization of fluorotetraphenylbismuth (1) has been achieved for the first time, revealing that the bismuth center of 1 adopts a distorted trigonal bipyramidal geometry with three ipso carbons at the equatorial sites and one ipso carbon and fluorine atom at the apical sites. Contrary to the previous common understanding of this type of organobismuth(V) compound, 1 was found to be thermally stable, maintaining its amphiphilic property. Hence, 1 can be used as an off-the-shelf reagent in organic synthesis, and its utility has been clearly demonstrated in applications to the efficient alpha-phenylation of ketones and esters.

New, improved procedure for the synthesis of structurally diverse N-spiro C2-symmetric chiral quaternary ammonium bromides.

Selective, direct ortho magnesiation of (S)-2,2'-bis(isopropoxycarbonyl)-1,1'-binaphthyl (6) has been achieved under mild conditions, using magnesium bis(2,2,6,6-tetramethylpiperamide) [Mg(TMP)(2)]. In combination with the subsequent reaction with the appropriate electrophiles, bromine and iodine, this method constitutes a key step in establishing a new and concise synthetic route to a wide variety of N-spiro C(2)-symmetric chiral quaternary ammonium bromides of type 1.

Design of N-spiro C2-symmetric chiral quaternary ammonium bromides as novel chiral phase-transfer catalysts: synthesis and application to practical asymmetric synthesis of alpha-amino acids.

A series of C(2)-symmetric chiral quaternary ammonium bromides 10 and 11 have been designed as a new, purely synthetic chiral phase-transfer catalyst, and readily prepared from commercially available optically pure 1,1'-bi-2-naphthol as a basic chiral unit. The details of the synthetic procedures of each requisite chiral binaphthyl subunit have been disclosed, and the structures of the assembled N-spiro chiral quaternary ammonium bromides 11a and 11f were unequivocally determined by single-crystal X-ray diffraction analysis. The reactivity and selectivity of these chiral ammonium bromides as chiral phase-transfer catalysts have been evaluated in the asymmetric alkylation of the benzophenone Schiff base of glycine ester 7 under mild liquid-liquid phase-transfer conditions, and the optimization of the reaction variables (solvent, base, and temperature) has also been conducted.

Asymmetric skeletal rearrangement of symmetrically alpha,alpha-disubstituted alpha-amino aldehydes: a new entry to optically active alpha-hydroxy ketones.

A unique asymmetric skeletal rearrangement of symmetrically alpha,alpha-disubstituted alpha-amino aldehydes has been accomplished for the first time using a chiral organoaluminum Lewis acid 1. For instance, treatment of (S)-2,2'-bis(trifluoromethanesulfonylamino)-1,1'-binaphthyl with Me3Al (1.0 equiv) in toluene at room temperature for 15 min and at 110 degrees C for an additional 15 min produced (S)-1, and a subsequent reaction with alpha -amino aldehyde 2a (R = CH2Ph) at -78 degrees C for 4 h and at -40 degrees C for 12 h resulted in the smooth rearrangement to the zwitterionic iminium intermediate A, which furnished the alpha-hydroxy ketone 3a (R = CH2Ph) in 93% isolated yield with 95% ee (S) after acidic hydrolysis.

Designer chiral quaternary ammonium bifluorides as an efficient catalyst for asymmetric nitroaldol reaction of silyl nitronates with aromatic aldehydes.

Designer chiral quaternary ammonium bifluoride 1 has been prepared, and both its catalytic and its chiral efficiency have been clearly demonstrated by achieving the first catalytic asymmetric nitroaldol reaction of silyl nitronate with aldehydes. For instance, the reaction of trimethylsilyl nitronate 2 (R(1) = Me) with benzaldehyde (R(2) = Ph) in THF in the presence of (S,S)-1 (2 mol %) proceeded smoothly at -78 degrees C, giving the corresponding nitroaldol adduct 3 (R(1) = Me, R(2) = Ph) in 92% isolated yield (anti/syn = 92:8) with 95% ee (anti isomer). The method was found to be successfully applicable to other aromatic aldehydes and silyl nitronates, and a high level of anti selectivity and enantiomeric excess was constantly observed.

Bis(((S)-binaphthoxy)(isopropoxy)titanium) oxide as a mu-oxo-type chiral Lewis acid: application to catalytic asymmetric allylation of aldehydes.

A new, chiral bis-Ti(IV) oxide of type 1 was successfully designed and can be utilized for strong activation of aldehyde carbonyls, thereby allowing a new catalytic enantioselective allylation of aldehydes with allyltributyltin. The chiral bis-Ti(IV) catalyst (S,S)-1 can be readily prepared either by treatment of bis(triisopropoxy)titanium oxide with (S)-binaphthol or by reaction of ((S)-binaphthoxy)isopropoxytitanium chloride with silver(I) oxide. Reaction of hydrocinnamaldehyde with allyltributyltin (1.

Submacular deposition of triamcinolone acetonide after triamcinolone-assisted vitrectomy.

Purpose: We describe a case demonstrating a submacular deposition of triamcinolone acetonide (TA) after a TA-assisted vitrectomy for retinal detachment.

Design: Interventional case report.

Methods: A 48-year-old Japanese man with rhegmatogenous retinal detachment in his left eye underwent a TA-assisted vitrectomy, endolaser photocoagulation, and sulfur hexafluoride (SF(6)) gas tamponade.

Catalytic enantioselective allylation of ketones with novel chiral bis-titanium(IV) catalyst.

Our recently designed chiral bis-titanium(IV) catalyst can be successfully utilized for the catalytic enantioselective allylation of ketones with tetraallyltin. The high asymmetric induction is achievable in the case of aromatic ketones.

Practical Oppenauer (OPP) oxidation of alcohols with a modified aluminum catalyst.

[reaction: see text] Modified aluminum catalyst 2 was found to be highly effective for Oppenauer (OPP) oxidation of alcohols under mild conditions. For example, oxidation of carveol in toluene with t-BuCHO (1.2 equiv) as a hydride acceptor in the presence of 2 (1 mol %) proceeded smoothly at 21 degrees C to give carvone in 94% yield after 1 h.

Asymmetric induction in the Neber rearrangement of simple ketoxime sulfonates under phase-transfer conditions: experimental evidence for the participation of an anionic pathway.

Phase-transfer catalysis has been successfully utilized for the Neber rearrangement of simple ketoxime sulfonates. For instance, treatment of (Z)-1a with p-toluenesulfonyl chloride (1.2 equiv), tetrabutylammonium bromide (5 mol %) and MeOH (10 equiv) in toluene-50% KOH aqueous solution (volume ratio = 3:1) at 0 degrees C for 2 h, and subsequent benzoylation followed by acidic hydrolysis afforded the protected alpha-amino ketone 2a in 80% isolated yield.

Prospective evaluation of suspected stenoocclusive disease of the intracranial artery: combined MR angiography and CT angiography compared with digital subtraction angiography.

Background And Purpose: MR angiography is primarily and increasingly used to assess intracranial arterial stenoocclusion. However, MR angiography can cause overestimation of stenosis. Although CT angiography is accurate, it has limitations.

Intraarterial chemotherapy or chemoembolization for locally advanced and/or recurrent hepatic tumors: evaluation of the feeding artery with an interventional CT system.

Purpose: To evaluate the utility of an interventional CT system for intraarterial chemotherapy or chemoembolization for locally advanced and/or recurrent hepatic tumors.

Methods: Thirty-eight patients with locally advanced or recurrent hepatic tumors underwent 73 intraarterial contrast-enhanced CT (IA-CECT) examinations immediately before chemotherapy or chemoembolization. The degree of tumor vascularity on angiography and enhancement on IA-CECT was classified into three grades: no, mild, or marked vascularity.

Distinct advantage of the in situ generation of quaternary ammonium fluorides under phase-transfer conditions toward catalytic asymmetric synthesis.

[structure in text] Quaternary ammonium fluorides were found to be efficiently generated in situ from the corresponding ammonium hydrogensulfates by treatment with commercially available potassium fluoride dihydrate (KF.2H(2)O) in THF and directly used as a fluoride source for the generation of carbon nucleophiles from organosilicon compounds. This method can be successfully applied to the preparation of structurally well-defined, C(2)-symmetric chiral quaternary ammonium fluorides of type 1 (X = F), thereby allowing catalytic enantioselective Mukaiyama-type aldol reactions under mild conditions.