10.1016/S0040-4020(97)00377-3
The study presents an enantioselective synthetic route to trans-2,6-disubstituted piperidines, focusing on the synthesis of (S)-2-methyl tetrahydropyridine-N-oxide, a key intermediate. This compound is crucial for constructing trans-2,6-disubstituted piperidines via a [3+2] nitrone cycloaddition reaction. The research demonstrates the utility of this method by synthesizing the fire ant venom alkaloid, (+)-solenopsin-A, through a series of steps including nitrone formation, cycloaddition, and reductive cleavage. The methodology is highlighted for its potential application in synthesizing similar piperidine-based alkaloids, with implications for pharmaceuticals, such as treatments for Alzheimer's disease.
10.1021/jo951643d
The study investigates the semi-π analogue of double hyperconjugation, known as "hyperconjugation/conjugation," in 4-isopropylidenecyclohexyl mesylate (4-OMs) and compares it with the saturated analogue, trans-4-isopropylcyclohexyl mesylate (5-OMs). The researchers found that the unsaturated substrate 4-OMs reacts only four times faster than the saturated substrate 5-OMs in 97% trifluoroethanol, indicating no significant through-bond interaction of the double bond with the reactive center. This is attributed to less than ideal overlap of the γ,δ π orbitals with the R, σ orbitals. However, when an electron-rich tin atom is attached to the 4-position, it provides a large rate enhancement and changes the mechanism to carbocation formation through double hyperconjugation. The study concludes that the π bond does not effectively stabilize positive charge through two stages of conjugation in the studied system, suggesting that the hyperconjugation/conjugation mode may not be a viable mechanism under the given conditions.
10.1016/j.tetlet.2008.05.112
The research presents a stereoselective synthesis of (2S,3S)-sa?ngol and its natural (2S,3R)-isomer from 3,4,6-tri-O-benzyl glycals. The key step in the synthesis involves a one-pot reduction of an azide, saturation of double bonds, and debenzylation under catalytic hydrogenation. The synthesis route leverages carbohydrate-based chiral pool starting materials to construct both stereocenters with good overall yields of 21% and 36%, respectively. Reactants used include 3,4,6-tri-O-benzylated glycals, which undergo Perlin hydrolysis and acetylation to form trans-enals. These are then subjected to Wittig reaction to yield trans dienes, which are further converted to the final products through a series of reactions involving sodium methoxide, mesyl chloride, sodium azide, and catalytic hydrogenation with palladium on carbon. Analyses used to characterize the synthesized compounds include spectral data such as infrared (IR), nuclear magnetic resonance (NMR), and high-resolution mass spectrometry (HRMS), which were found to be in good agreement with reported data of the natural materials.
10.1039/c0cc00616e
The research focuses on the synthesis and characterization of highly fluorinated, water-soluble cyclodextrins and their interactions with both fluorinated and non-fluorinated guest molecules. The cyclodextrins were synthesized through a three-step process: perchlorination at C6 using methylsulfonylchloride, functionalization with trifluoroethylthiol in the presence of NaH, and finally, reaction with triethyleneglycol p-toluenesulfonate ester in the presence of NaH. The synthesized cyclodextrins were analyzed using isothermal titration calorimetry (ITC) and NMR spectroscopy to determine their binding constants, thermodynamic parameters, and stoichiometry with various guest molecules. The results indicated that the fluorinated cyclodextrins preferentially interacted with fluorinated guests, demonstrating the significant role of the fluorophobic effect in stabilizing host-guest complexes in water.
10.1016/S0040-4039(00)99185-8
The research presents a novel method for synthesizing the side chain of brassinolide, a plant growth regulator. The primary purpose of this study was to develop a stereocontrolled synthesis of the brassinolide side chain, which is challenging due to the presence of four contiguous chiral centers. The researchers utilized pyranone derivatives as versatile intermediates to achieve this goal. Key chemicals involved in the synthesis include 20-carboxaldehyde, Z-lithiofuran, pyridinium chlorochromate, ethoxyethyl ethers, lithium dimethylcuprate, lithium diisopropylamide, methyl iodide, sodium borohydride, lithium aluminum hydride, methanesulfonyl chloride, and acetic anhydride. The study successfully demonstrated a stereocontrolled synthesis route, starting from the addition of Z-lithiofuran to 20-carboxaldehyde to produce furylcarbinols, followed by a series of oxidation, reduction, and protection steps to construct the pyranone derivative. Subsequent reactions, including conjugate addition and selective methylation, led to the formation of the desired side chain. The final conversion of the synthesized side chain into brassinolide was achieved through a series of known steps, thus completing the formal synthesis of brassinolide. The conclusions highlight the effectiveness of using pyranone derivatives as intermediates for the stereocontrolled synthesis of complex polyhydroxylated steroid side chains, providing a new and efficient method for constructing the brassinolide side chain.
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