Synthesis and structural characterization of enantiopure (2R,5R)-(+)-2,5-dimethylthiolane

Enantiopure (2R,5R)-(+)-2,5-dimethylthiolane was synthesized by cyclization with sodium sulfide of the dimesylate of (2S,5S)-(+)-2,5-hexanediol, which was obtained by baker's yeast (Saccharomyces cerevisiae) reduction of acetonyl acetone in high enantiomeric purity. The structure of the diol and absolute stereochemistry of the sulfone derived from the title molecule were determined by X-ray crystal structure analysis.     

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 (+)-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.     

Synthesis of (+)-galiellalactone. Absolute configuration of galiellalactone

[reaction: see text]. (+)-Galiellalactone was synthesized starting from (R)-(+)-pulegone. Natural and synthetic galiellalactone have opposite optical rotations, demonstrating that the structure of the natural product is 1a.     

Absolute configuration of tert-butyl-1-(2-methylnaphthyl)phosphine oxide

The enantiomers of tert-butyl-1-(2-methylnaphthyl)phosphine oxide 1 have been separated using a homemade HPLC column and an analytical gradient system. Vibrational absorption and circular dichroism spectra for both enantiomers have been measured in CD2Cl2 and CH2Cl2 solutions in the 2000-900 cm(-1) region. The fully relaxed potential energy surface of (S)-tert-butyl-1-(2-methylnaphthyl)phosphine oxide, obtained using the B3LYP functional with a 6-31G basis set, indicated two stable conformers with their populations in a approximately 2:1 ratio. The vibrational absorption and VCD spectra are predicted for these two conformers using the B3LYP functional with a 6-31G basis set. The comparison of predicted and experimental spectra indicated that (+)-tert-butyl-1-(2-methylnaphthyl)phosphine oxide is in the (S)-configuration. This assignment is supported by the ab initio prediction of positive optical rotation for the most stable conformer with an (S)-configuration and the nonequivalence sense of the tert-butyl group chemical shift observed in the 1H NMR spectrum of this enantiomer measured in the presence of (+)-(S)-mandelic acid as a chiral solvating agent.     

Enantioselective total syntheses of (+)- and (−)-ottelione A and (+)- and (−)-ottelione B. Absolute configuration of the novel, biologically active natural products

Following our recent total synthesis of the biologically potent natural products otteliones A and B in racemic form, we have now accomplished the total synthesis of both the enantiomers of otteliones A and B through an enantiodivergent strategy emanating from the readily available Diels-Alder adduct of cyclopentadiene and p-benzoquinone. These endeavors have led to the elucidation of the absolute configuration of naturally occurring otteliones A and B.     

The absolute configuration and circular dichroism of (+)-(1,5)-diamino-triptycene

The absolute configuration of(+)-(1,5)-diamino-triptycene has been determined by calculation of the CD spectrum of the molecule and comparison with the experimental results of Tanaka et al.⁴ To achieve this the exciton theory of Weigang and Nugent³ has been extended to include terms representing the retardation of the electro-magnetic wave in the chromophores. The final results of the present study are in contradiction with those of Tanaka et al.^4a,b,c     

Synthesis and configuration of diastereomeric 1-(β-dimethylaminoethyl)-2,5-dimethyl-4-plperidols

Diastereomeric 1-(-dimethylaminoethyl)-2,5-dimethyl-4-piperidols were synthesized and their configurations were studied. The spatial orientation of the substituents in the , , and isomers of 2,5-dimethyl-4-piperidol was established, and the stereochemistry of the reduction of 2,5-dimethyl-4-piperidone with sodium in alcohol, with lithium aluminum hydride, and by catalysis on Raney nickel was studied by PMR spectroscopy. A series of transformations at the nitrogen atom of the piperidine ring do not change the configuration of 2,5-dimethyl-4-piperidols, but the stereochemistry of the reduction of the keto group in 2,5-dimethyl-4-piperidones with lithium aluminum hydride depends markedly on the character of the substituent attached to the piperidine nitrogen.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1374–1378, October, 1973.     

Absolute configuration and conformational disorder of a tricyclic thio­semicarbazone derivative

The title compound, (1S,3R,8R)‐2,2‐dichloro‐3,7,7,10‐tetra­methyl­tricyclo­[6.4.0.0^1,3]­dodecan‐11‐one thio­semicarbazone, C₁₇H₂₅Cl₂N₃S, has two disordered conformations of the cyclo­heptane moiety and a screw‐boat conformation for the cyclo­hexene ring. The absolute configuration was established.     

Enantioselective synthesis and absolute configuration assignment of gabosine O. Synthesis of (+)- and (-)-gabosine N and (+)- and (-)-epigabosines N and O

[reaction: see text] A rational approach to the synthesis of gabosines and other related carba-sugars starting from a masked p-benzoquinone has been designed. The enantioselective acetylation of the hydroxyketal 2 provides a practical entry to either enantiomer of the target products. The strategy has been applied to the synthesis of (+)- and (-)-gabosines N and O and (+)- and (-)-epigabosines N and O. The absolute configuration of natural gabosine O has been established.     

Synthesis,Crystal Structure and Absolute Configuration of (+)-(a-Hydroxybenzyl)phenylphosphinic acid

1 INTRODUCTION a-Hydroxyphosphonic acids and their esters are known to possess broad-based physiological activities and there is close links between biological efficacy and stereochemistry[1~3]. Optical active a-hydroxyphosphonic esters can also serve as useful precursors in organic synthesis[4, 5]. Here we will report the synthesis of optical active a-hydroxyphosphinic acid, (+)-(a-hydroxybenzyl)- phenylphosphinic acid and its crystal structure and the absolute configuration of its a-ca…     

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.