Synthesis of chiral acetoxy lactones via the Baeyer-Villiger oxidation of cyclic aromatic acetoxy ketones

The α-acetoxylation of indanones and tetralones by using Mn(OAc)₃ followed by the enzyme catalyzed kinetic resolution of acetoxy ketones furnished both of the enantiomers of α-acetoxy ketones in good chemical and optical yields. The Baeyer-Villiger oxidation of α-acetoxy ketones with m-CPBA, CF₃SO₃H, and CH₂Cl₂, at rt gives the corresponding lactones without racemization. The acetoxy ketone moiety migrates selectively in order to form lactones. The mild hydrolysis of lactones affords phenolic α-hydroxycarboxylic acid derivatives.     

New method of reducing lactones and esters of aldonic acids to sugars

Summary A simple, general method of reducing esters and lactones of aldonic acids to sugars by the action of sodium amalgam, according to which the process is conducted in the presence of a strong cation exchange resin to maintain optimum pH, has been proposed.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya No. 11, pp. 2095–2096, November, 1964     

Efficient and selective synthesis of glycofuranosyl azides and nucleosides from cyclic 1,2-thiocarbonate sugars

[reaction: see text] Cyclic 1,2-thiocarbonate sugars are convenient starting materials for the selective and efficient preparation of glycofuranosyl azides and nucleosides by regio- and stereoselective thiocarbonate ring-opening.     

Catalytic atropo-enantioselective reduction of biaryl lactones to axially chiral biaryl compounds

The atropo-enantioselective borohydride reduction with dynamic kinetic resolution of biaryl lactones was catalyzed by an optically active beta-ketoiminatocobalt(II) complex to afford optically active biaryl compounds. Chiral HPLC analysis of the starting biaryl lactones was performed at various temperatures to determine suitable reaction conditions for dynamic kinetic resolution. Various types of axially chiral biaryl compounds were obtained with high enantioselectivity.     

Substituted lactones and their transformations; IV. Hydrogenation of substituted lactones to alkyltetrahydrofurans

To make a comparative study of the connection between odor and structure in the alkyl--butyrolactone and alkyltetrahydrofuran series, -,-, and ,-dialkylbutyrolactones are hydrogenated over copper-chromium catalyst to give the corresponding tetrahydrofurans. Most of the compounds obtained retain a fruity odor, reminiscent of that of the starting lactones.For Part III see [1].     

Synthesis of cyclic mono- and bis-disulfides and their selective conversion to mono- and bis-thiosulfinates

Twelve-membered ring pseudopeptidic cyclic disulfides have been prepared by iodine oxidation of the parent dithiols. However, oxidation of N,N′-(1,2-phenylene)bis(2-mercapto-2-methylpropanamide) afforded a 25/75 mixture of cyclic mono- and bis-disulfides that were separated by selective precipitation in CHCl₃. The cyclic bis-disulfide was selectively prepared by iodine oxidation of the Ni complex of this dithiol and crystallized. Its crystal structure was solved by X-ray diffraction. All these cyclic mono- or bis-disulfides were selectively converted to cyclic mono- and bis-thiosulfinates upon stoichiometric oxidation with dimethyldioxirane at low temperature. ¹H NMR of the cyclic bis-thiosulfinate revealed the presence of four isomers, two couples of stereoisomers, as expected from the insertion of two oxygen atoms in this compound, one on each disulfide bond. The two couples of cis/trans isomers were separated by preparative TLC and identified after alkaline cleavage of the two S(O)-S bonds and metalation with Ni(II). As HO⁻ attack is selective for the sulfinyl sulfur, the nature of the Ni complexes obtained is a signature of each couple of stereoisomers.     

Synthesis and selective recognition toward zinc ion of chiral poly(imine‐triazole)

A novel AB type of clickable monomer, (S)‐2‐[(2‐azido‐1‐phenylethylimino)methyl]‐5‐propargyloxyphenol (AMPP) was designed and polymerized to yield a class of main‐chain chiral poly(imine‐triazole)s through the metal‐free click reaction. With the thermally induced polymerization, the desired polytriazoles can be easily prepared in high yields by a stepwise heating‐up process and have the number‐average molecular masses ranging from 5.1 × 10³ to 58.1 × 10³ (polydispersity indices = 1.38?1.68). The polymers were characterized by Fourier Transform Infrared spectroscopy (FTIR), ¹H Nuclear Magnetic Resonance (NMR), and gel permeation chromatography, and their optical properties were studied by fluorescence and circular dichroism (CD) spectroscopies. As a chemosensor, these polymers exhibited a selective “turn‐on” fluorescence enhancement response toward Zn²⁺ ion over other cations such as Na⁺, K⁺, Mg²⁺, Ca²⁺, Ag⁺, Pb²⁺, Cd²⁺, Hg²⁺, Mn²⁺, and Ni²⁺ in dimethyl sulfoxide. However, the Zn²⁺‐induced fluorescence signal was subject to serious interference by Al³⁺, Cu²⁺, Cr³⁺, and Fe³⁺ ions. Interestingly, the chiral polymer showed distinctive changes in the CD spectra on complexation with Zn²⁺, which allowed for the discrimination of this ion in the presence of other species tested including those interfering ions observed in the fluorescent detection. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 2248–2257     

Ring fission of chiral cyclic acetals plus intramolecular [4 + 2] cycloaddition: a sequential access to medium-size lactones. Application to the synthesis of carbasugars

A set of alpha,beta-unsaturated cyclic acetals were reacted with t-butyllithium in THF. A conjugate elimination took place, triggering a ketal ring cleavage when two eq. of TMEDA were added to the medium. The lithium alcoholate thus obtained could be trapped in situ by 2,2,2-trifluoroethyl acrylate. The resulting acryloyl (1Z,3E)-dienyl ether was then submitted to an intramolecular Diels-Alder cycloaddition under high pressure (12 kbar, 50 degrees C). Depending on the structure of the linkage between the diene and the acrylate, the expected ("fused") lactones were obtained with total endo- or exo-selectivities and high to complete diastereoselectivities. A remarkable inversion of selectivity, from endo to exo, with respect to the stereochemical elements of the tether could be observed in these cases. A five step diastereoselective transformation of two of the resulting nine-membered ring lactones into modified carbasugars was finally achieved in 23% overall yield.     

One-step synthesis of inherently chiral p-tert-butylcalix[4]azacrown

A one-step procedure is developed to synthesize inherently chiral p-tert-butylcalix[4]azacrown 1 through etherification between p-tert-butylcalix[4]arene and compound 3, which can be amplified to efficiently prepare more inherently chiral calix[4]arenes in ABHH substitution pattern.     

Oxidative decarboxylation of cyclic amino acids and dehydrogenation of cyclic secondary amines with iodosobenzene

Cyclic amino acids L-proline, pipecolinic acid and L-2-pyrrolidinone-5-carboxylic acid undergo oxidative decarboxylation with iodosobenzene in various solvents (including water) to yield the lactam and imide in the latter case. The reaction proceeds via initial imine formation.     

Synthesis of novel chiral [2.2.1]cryptands incorporating sugars

Chiral N, N'-dimethyl diaza-crown ethers bearing functionalized α-D-gluco-, α-D-galacto-, and α-D-mannopyranoside residues are transformed into the corresponding [2.2.1]cryptands with bis(2-iodoethyl) ether under high-pressure conditions and subsequent demethylation. Alternatively, α-D-manno-diaza-18-crown-6 reacts with diglycolic acid dichloride under high-dilution conditions to form bisamide which is reduced to the corresponding chiral [2.2.1]cryptand.     

One-step conversions of a simple corrole into chiral and amphiphilic derivatives

The reactions of phosgene with 5,10,15-tris(pentafluorophenyl)corrole and its gallium(III) complex lead to a novel chiral macrocycle and an amphiphilic corrole, respectively. Both types of molecules were fully characterized by spectroscopy and X-ray crystallography.     

Physiochemical pathway for cyclic dehydrogenation and rehydrogenation of LiAlH4

A five-step physiochemical pathway for the cyclic dehydrogenation and rehydrogenation of LiAlH4 from Li3AlH6, LiH, and Al was developed. The LiAlH4 produced by this physiochemical route exhibited excellent dehydrogenation kinetics in the 80-100 degrees C range, providing about 4 wt % hydrogen. The decomposed LiAlH4 was also fully rehydrogenated through the physiochemical pathway using tetrahydrofuran (THF). The enthalpy change associated with the formation of a LiAlH4.4THF adduct in THF played the essential role in fostering this rehydrogenation from the Li3AlH6, LiH, and Al dehydrogenation products. The kinetics of rehydrogenation was also significantly improved by adding Ti as a catalyst and by mechanochemical treatment, with the decomposition products readily converting into LiAlH4 at ambient temperature and pressures of 4.5-97.5 bar.     

A stereospecific synthesis of chiral cyclic sulfinamides

Treatment of racemic or enantiomerically pure 2,1-benzothiazines (cyclic sulfoximines) with lithium triethylborohydride results in clean loss of the S-aryl group with complete retention of configuration at sulfur to produce diastereomerically and/or enantiomerically pure cyclic sulfinamides in excellent yield.     

Light-driven twisting behaviour of chiral cyclic compounds

Chiral cyclic compounds exhibited light-driven twisting by means of trans-cis photoisomerization in 1,4-dioxane solution, a neat film, and a liquid-crystalline host.