Determination of absolute configuration using vibrational circular dichroism spectroscopy: the chiral sulfoxide 1-(2-methylnaphthyl) methyl sulfoxide

We report the determination of the absolute configuration (AC) of the chiral sulfoxide, 1-(2-methylnaphthyl) methyl sulfoxide, 1, using vibrational circular dichroism (VCD) spectroscopy. The VCD of 1 has been measured in the mid-IR spectral region in CCl(4) solution. Analysis employs the ab initio DFT/GIAO methodology. DFT calculations predict two stable conformations of 1, E and Z, Z being lower in energy than E by <1 kcal/mol. In both conformations the S-O bond is rotated from coplanarity with the naphthyl moiety by 30-40 degrees. The predicted unpolarized absorption ("IR") spectrum of the equilibrium mixture of the two conformations permits assignment of the experimental IR spectrum in the mid-IR spectral region. The presence of both E and Z conformations is clearly evident. The VCD spectrum predicted for S-1 is in excellent agreement with the experimental spectrum of (-)-1, unambiguously defining the AC of 1 as R(+)/S(-).     

Absolute configuration determination of 2-(2-oxo-3-indolyl)acetamide derivatives

We describe a reliable method for determining the absolute configuration of 2-(2-oxo-3-indolyl)acetamides based on analysis of the ¹H NMR spectra of their phenylethylamide diastereomers. The conformational preferences for two diastereomeric amides were calculated by DFT, which matched well with the experimental results. X-ray diffraction analysis allowed us to validate the method.     

Absolute configuration of 2-(tributylstannyl)pyrrolidine by anomalous dispersion X-ray analysis

Enantiopure 2-(tributylstannyl)pyrrolidine hydroiodide may be prepared in excellent yield by TMSI treatment of the corresponding N-Boc compound, which is in turn prepared by asymmetric deprotonation (s-BuLi.sparteine) and stannylation, as described in the literature. Crystals of the hydroiodide salt suitable for X-ray analysis were obtained, and although there is some disorder about the butyl groups, analysis using anomalous dispersion establishes the absolute configuration as S.     

Absolute configuration of anti-HIV-1 agent (-)-concentricolide: total synthesis of (+)-(R)-concentricolide

The first enantioselective total synthesis of (+)-(R)-concentricolide, the enantiomer of an anti-HIV-1 agent isolated from Daldinia concentrica, from 2-iodophenol in 7 steps reveals the (S)-configuration for the natural form of the furanophthalide. The key features include an anionic ortho-Fries rearrangement to furnish 3-iodosalicylamide, facile construction of the benzofuran system employing the tandem Sonogashira coupling annulation reaction, directed ortho metalation to introduce a propanoyl group, as well as CBS reduction, establishing the stereocenter enantioselectively.     

Absolute configuration of 2-hydroxy-2-(1-naphthyl)propionic acid as determined by the 1H NMR anisotropy method

Enantiopure 2-hydroxy-2-(1-naphthyl)propionic acid (+)-2 was prepared by the stereoselective Grignard reaction of 1-naphthylmagnesium bromide with (1R,3R,4S)-menthyl pyruvate 3 or (1R,3R,4S)-8-phenylmenthyl pyruvate 4, and the absolute configuration of acid (+)-2 was unambiguously determined to be S by the ¹H NMR anisotropy method.     

Absolute configuration of (+)-1-amino-1-methylpropylphosphonic acid

Conclusion The absolute configuration of (+)-1-amino-1-methylpropylphosphonic acid and its (+)-diethyl ester is S in the Cahn -Ingold -Prelog system.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 12, pp. 2821–2823, December, 1986.     

Absolute configuration of 2-methoxy-2-(2-naphthyl)propionic acid as determined by the 1H NMR anisotropy method

2-Methoxy-2-(2-naphthyl)propionic acid 1 and 2-hydroxy-2-(2-naphthyl)propionic acid 2 were prepared by the Grignard reaction of 2-naphthylmagnesium bromide with (1R,2S,5R)-(−)-menthyl pyruvate. The absolute configurations of (+)-1 and (+)-2 were determined to be S by the ¹H NMR anisotropy method.     

Absolute configuration of D(2)-symmetric fullerene C(84)

The D(2)-symmetric isomer of fullerene C(84) predominantly found in soots is inherently chiral. We determine its absolute configuration by comparison of the experimental electronic circular dichroism (CD) spectrum with time-dependent density functional calculations.     

Investigation of reactions in carboxyl-terminated polybutadiene and tris-[1-(2-methyl)aziridinyl] phosphine oxide

The functionalities of a series of carboxyl-terminated polybutadiene samples (CTPB) were calculated from an infrared spectroscopic study of the samples reacting to the gel point with tris-[1-(2-methyl)aziridinyl] phosphine oxide (MAPO), Epon X801, and glycerol. Identical functionalities were calculated when Epon X801 and glycerol were used as curing agents. Higher functionalities for CTPB with MAPO were due to additional reactions that MAPO underwent with hydroxyl groups and water, present in carboxyl-terminated polybutadiene, and with itself (homopolymerization). Rate constants were calculated for the homopolymerization of MAPO in Nujol, in nonfunctional polybutadiene, and in CTPB. The homopolymerization resulted in an increase and then a gradual decrease in MAPO functionality, which was in agreement with that predicted from theoretical considerations.     

Optically active Phosphine oxides : Synthesis and absolute configuration of (menthoxycarbonylmethyl) phenylvinyl phosphine oxide

The enantiomeric(-)(menthoxycarbonlymethyl)phenylvinylphosphine oxide 1b has been prepared and its absolute configuration rigorously established via chemical correlation. One-step decarbalkoxylation of (-)-ethyl(methoxycarbonylmethyl)phenyphosphine oxide 6 was effected with LiCl-H₂O-DMSO and shown to proceed without concomitant racemization at phosphorus.     

Absolute configuration and conformational stability of (+)-2,5-dimethylthiolane and (-)-2,5-dimethylsulfolane

Enantiopure (+)-2,5-dimethylthiolane and (-)-2,5-dimethylsulfolane were prepared using literature procedures and investigated using vibrational circular dichroism (VCD). Experimental absorption and VCD spectra of (+)-2,5-dimethylthiolane and (-)-2,5-dimethylsulfolane in CCl(4) solution in the 2000-900 cm(-)(1) region were compared with the ab initio predictions of absorption and VCD spectra obtained with density functional theory using the B3LYP/6-311G(2d, 2p) basis set for different conformers of (2R,5R)-2,5-dimethylthiolane and (2R,5R)-2,5-dimethylsulfolane. This comparison indicates that (+)-2,5-dimethylthiolane is of the (2R,5R)-configuration and has two predominant conformations in CCl(4) solution. In addition, (-)-2,5-dimethylsulfolane is of (2R,5R)-configuration and has only one predominant conformation. The stereochemical assignment is in agreement with literature.     

Collagen cross-links: a convenient synthesis of tert-butyl-(2S)-2-[(tert-butoxycarbonyl)amino]-4-(2-oxiranyl)butanoate

An efficient synthesis of tert-butyl-(2S)-2-[(tert-butoxycarbonyl)amino]-4-(2-oxiranyl) butanoate (5), the key intermediate for preparation of collagen cross-links (+)-pyridinoline (Pyd, 1) and (+)-deoxypyridinoline (Dpd, 2) was described from (4S)-5-(tert-butoxy)-4-[(tert-butoxycarbonyl)amino]-5-oxopentanoic acid (6) in six steps. Also, an improved synthesis of iodide (2S)-(−)-4b was presented.     

Reaction of diphenyl[2-(triethoxysilyl)ethyl]phosphine oxide with boron trifluoride etherate

Diphenyl[2-(trifluorosilyl)ethyl]phosphine oxide was synthesized by the reaction of diphenyl[2-(triethoxysilyl)ethyl]phosphine oxide with boron trifluoride etherate. As shown by the ¹H, ¹³C, ¹⁹F, ³¹P, ²⁹Si multinuclear NMR spectroscopy data, the silicon atom in the molecule is tetracoordinate. The absence of P=O→Si interaction in diphenyl[2-(trifluorosilyl)ethyl]phosphine oxide, as follows from the comparison of the calculated [GIAO B3LYP/6-311++G(2d,p)] and experimental δ(²⁹Si) and δ(³¹P) values, is due to the formation of complex with BF₃ by the phosphoryl oxygen.     

Determination of the Absolute Configuration of 1-[(4-(Bromomethyl)phenyl]-2-(prop-2-yn-1-yloxy)ethanol

Russian Journal of Organic Chemistry - The reaction of chloromethyl propargyl ether with 4-(bromomethyl)benzaldehyde in the presence of zinc metal and a chiral ligand,...