Carboxylic acids tert-butyl esters

D. 2(S)-(fl-tert-Butoxycarbonyl-a-(R)-hydroxyethyl)-4-(R)-hydroxy-pyrrolidine- 1-carboxylic acid, tert-butyl ester. The identical procedure was followed, in this case using the (,S)-BINAP catalyst (5)-l. Hydrogenation is conducted for 64 hr, and the reaction mixture is then transferred to a 250-mL, round-bottomed flask and concentrated to dryness. The residue is dissolved in 17 mL of methanol and cooled to 15°C. After the slow addition of 7 mL of DI water, the solution is aged for 15 min gradually forming a thin slurry. More DI water (75 mL) is added over 1 hr and the mixture is allowed to stand for an additional 1 hr at 15°C. The resulting crystals (Note 19) are filtered at 15°C, washed with 10 mL of 1 4-MeOH water, and then dried overnight in a vacuum oven (35°C, 686 mm) to yield 7.0 g (70%) of (R)-hydroxy ester 4b (Note 20). 

S-4R)-2-tert-Butoxycarbonylacetyl-4-hydroxypyrrolidine-l-carboxylic acid, tert- butyl ester 2-Pyrrolidinepropanoic acid, l-[(l,l-dimethylethoxy)carbonyl]-4 hydroxy- P-oxo-, 1,1-dimethylethyl... 

The group of Jew and Park successfully utilized dihydrocinchonidine-derived 6f as an efficient catalyst for the asymmetric alkylation of o-biphenyl-2-oxazoline- and o-biphenyl-2-thiazoline-4-carboxylic acid tert-butyl esters (16a and 16b) under mild solid-liquid phase-transfer conditions (Scheme 2.13) [32,33]. These reactions are... 

The catalytic and chiral efficiency of (S,S)-le was also appreciated in the asymmetric synthesis of isoquinoline derivatives, which are important conformationally constrained a-amino acids. Treatment of 2 with a,a -dibromo-o-xylene under liquid-liquid phase-transfer conditions in the presence of (S,S)-le showed complete consumption ofthe starting Schiffbase. Imine hydrolysis and subsequent treatment with an excess amount of NaHCOs facilitated intramolecular ring closure to give 1,2,3,4-tetrahydroisoquinoline-3-carboxylic acid tert-butyl ester 38 in 82% yield with 98% ee. A variety of l,2,3,4-tetrahydroisoquinoline-3-carboxylic acid derivatives possessing different aromatic substituents, such as 39 and 40, can be conveniently prepared in a similar manner, with excellent enantioselectivity (Scheme 5.20) [25]. 

Jew and Park achieved a highly enantioselective synthesis of (2S)-a-(hydroxy-methyljglutamic acid, a potent metabotropic receptor ligand, through the Michael addition of 2-naphthalen-l-yl-2-oxazoline-4-carboxylic acid tert-butyl ester 72 to ethyl acrylate under phase-transfer conditions [38]. As shown in Scheme 5.36, the use of BEMP as a base at —60 °C with the catalysis of N-spiro chiral quaternary ammonium bromide le appeared to be essential for attaining an excellent selectivity. 

Carboxylic acid tert-butyl esters COOH -... 

Preparation of (5)-6-bromo-8-(3-prenyl)-3a-(3-oxo-propyl)-3,3a,8,8a-tetrahydro-2//-pyrrolo[2,3-6)indole-l-carboxylic acid tert-butyl ester (222) from A -lO-BOC-l-prenyl-6-bromotryptamine (220), acrolein (213), and MacMillan catalyst 211A... 

Typical procedure. 4-Bromo-3-[2-isocyano-2-(methoxycarbonyl)ethyl]ir dole-l-carboxylic acid tert-butyl ester 1559 [1187] The N-formyl-N -Boc-4 -bromo-tryptophan methyl ester 1558 (0.05 g, 0.14 mmol) was suspended in dry dichloromethane (3 mL) under argon and the solution was cooled to below 0 °C using an ice/salt bath. Tri-ethylamine (0.09 g, 0.86 mmol) was added through a septum, and then a solution of triphosgene (0.014 g, 0.05 mmol) in dichloromethane (1 mL) was added dropwise. The solution was allowed to warm to room temperature and stirred for a further... 

Phosphine-AgOTf complexes are known to promote Michael addition reactions. Kobayashi and Shirakawa have achieved asymmetric Michael addition of P-ketoester to nitroalkenes catalyzed by (R)-Tol-BINAP-AgOTf in water [68]. When cyclopentanone-2-carboxylic acid tert-butyl ester (50) and trans- -nitrostyrene (51) were used as substrates, the Michael adduct (52) was obtained in 71% yield with 77 23 diastereomeric ratio. The major diastereomer showed 78% ee (Scheme 18.19). 

Typical experimental procedure for (S)-3-(l,3-dioxo-l,3-dihy-dro-isoindol-2-yl)-3-fluoro-2-oxo-piperidin-l-carboxylic acid tert-butyl ester (precursor of 3S-fluorothalidomide) using the dihydroquinine/NFSI combination with TMEDA Lithium bis (trimethylsilyl)amide solution l.OM in THF (0.087mL, 0.087 mmol) was added to the solution of 3-(l,3-dioxo-l,3-dihydro-iso-indol-2-yl)-2-oxo-piperidin-l-carboxylic acid tert-hutyl ester (20 mg, 0.058 mmol) and tetramethylethylenediamine (0.013 mL, 0.087 mmol) in THF (l.OmL) at -80°C under Ar. After being stirred for 0.5 hours, the suspension of the dihydroquinine/NFSI combination [the solution of dihydroquinine (28.4 mg, 0.087 mmol) and N-fluorobenzenesulfonimide (27.4 mg, 0.087 mmol) in THF (2.0 mL) was stirred for 1 hour at room temperature under Ar] was dropwise and then stirred for overnight at -80 °C. The reaction was quenched with IN hydrochloric acid, extracted with ethyl acetate, washed with brine, dried over Na2S04 and concentrated under reduced pressure. The residue was purified by silica-... 

C10H13NO2 pyridine-3-carboxylic acid tert-butyl ester 65321-36-0... 

The Maruoka group described an efficient enantioselective synthesis of optically active a-methyl serine derivatives by using their structurally simpHfied catalyst (S)-36b under mild phase-transfer conditions [107]. The asymmetric synthesis of a-alkyl cysteines, a-alkyl-a,p-diamino propionic acids, a-alkyl homoserines, and a-alkyl homocysteines was also carried out via the asymmetric phase-transfer catalytic a-alkylation of thiazoline-4-carboxylic acid tert-butyl esters 75, imidazoHne-4-carboxylic acid tert-butyl esters 76, and the six-membered ring substrates 77 and 78 [108]. 

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