A novel reaction cascade involving a Lewis acid-induced migration of an isopropylidene protecting group followed by the formation of a pyranose or furanose ring and subsequent reduction of the hemiacetal is described. Depending on the reaction conditions, as well as, the stereochemistry of the substrate, polyhydroxylated tetrahydrofurans or tetrahydropyrans can be obtained in reasonable yields. The synthons used in this transformation were prepared via a highly stereoselective one-pot tandem reaction, consisting of a 1,4-Michael addition of vinylmagnesium bromide to d-glucose-derived cyclohexenone followed by aldol reaction with 2,3-O-isopropylidene-d-glyceraldehyde. 相似文献
The development of novel methods and strategies for the formation of polycyclic ring structures is of utmost importance in organic synthesis. The present study describes the investigation of a transannular cyclization strategy for constructing bicyclic ring systems. To test the viability of the approach, the SmI2-mediated ketone-olefin coupling reaction, a method previously developed in this laboratory, was examined. Investigation of the transannular cyclization of cyclooctene, cyclodecene, and cycloundecene derivatives revealed that the process proceeds with high yield and diastereoselectivity, and in the case of larger ring-sized compounds, with excellent regioselectivity. The regioselectivity of the annulation process could be rationalized based on examining the low energy conformations of the keto alkene starting materials. These results demonstrate the efficiency and the potential of the transannular cyclization tactic for the creation of bicyclic ring systems. 相似文献
A three-step synthesis of enantiomerically enriched 1,1,1-trifluoro-2-propanamine based on the use of a chiral sulfinamide auxiliary is described. The reduction of the geometrically pure Z-sulfinimine (NOE, HOE) with NaBH4 or l-Selectride leads to the corresponding (R)- or (S)-configured amine derivatives (X-ray crystallographic analysis) with 92–96% de. The typical models to explain the stereoselection for these reducing agents fail to rationalize the obtained stereoselectivities, and an in situ imine isomerization is proposed to occur. The direct use of the hydrochloric acid salt (with excess Et3N) of this poorly nucleophilic amine for epoxide opening reactions is not possible due to the higher nucleophilicity of chloride. Hence, a novel triflate salt is introduced, synthesized through ready sulfinamide hydrolysis with trimethylsilyl triflate, which can be used directly, without the need of isolating the pure amine beforehand. 相似文献
A simple and efficient one-pot two-step synthesis of substituted 3-aminoarylquinolines has been achieved from 2-nitrobenzaldehyde and indoles under microwave irradiation. Firstly 2-nitrobenzaldehydes is reduced to 2-aminobenzaldehyde in situ by commonly used chemo selective reductant SnCl2 followed by condensation of indole. The acidic nature of the resultant reaction mixture due to SnCl2 helps in the condensation and facile ring opening of indole leading to the formation of 3-aminoarylquinoline derivatives in good to moderate yields. 相似文献
Enantiomerically pure (3S,7R,8aS)-3-phenyloctahydropyrrolo[1,2-a]pyrazine-7-ol, (3S,7R,8aS)-3-methyl octahydropyrrolo[1,2-a]pyrazine-7-ol, (3S,7R,8aS)-3-isopropyloctahydropyrrolo[1,2-a]pyrazine-7-ol and (3S,7R,8aS)-3-isobutyloctahydropyrrolo[1,2-a]pyrazine-7-ol 16d were synthesized via preparation of the corresponding cyclic amides from enantiomerically pure l-proline and hydroxyproline derivatives followed by reduction using sodium borohydride-iodine. 相似文献
A dioxidovanadium(V) complex of type [(LONOH?)(VO2)] (1) was isolated where LONOH2 is a tridentate ONO donor benzhydrazide ligand. 1 undergoes an oxo transfer reaction with triphenylphosphine in presence of 8-hydroxyquinoline (HQ) and affords a monooxidovanadium(V) complex of type [(LONO2?)(VO)(Q?)] (2). 1 and 2 were substantiated by elemental analyses, ESI-mass, IR, 1H NMR, 51V NMR and UV–vis spectra. The molecular geometries of 1 and 2 were authenticated by single crystal X?ray crystallography. UV–vis absorption spectra of 1 and 2 display bands respectively at 325 and 320 nm due to oxido → vanadium(V) charge transfer transitions. 1 exhibit an irreversible cathodic peak at ?0.44 V whereas 2 displays a reversible cathodic wave at ?0.60 V in cyclic voltammogram due to the VO3+/VO2+ redox couple. 相似文献
Cyclobutane forming [2+2]-cycloaddition reactions of allylsilane with electron-deficient olefin is promoted by triflic imide (Tf2NH). Triflic imide is converted in situ to silyl triflic imide (R3SiNTf2), which serves as the actual catalyst for this process. When these reactions take place at higher than ambient temperatures, thermodynamically more stable anti-cyclobutanes are generated preferentially by equilibration of the initially formed adducts via retro [2+2]-cycloaddition. 相似文献
Isoryanodane diterpenoids possess a densely oxygenated and intricately fused pentacycle (ABCDE-ring), although its unique ring system has not yet been assembled chemically. The 6/5/7-membered BCD-rings of isoryanodanes differ from the 5/6/6-membered rings of the structurally-related ryanodanes. We previously achieved the total synthesis of ryanodine and five other ryanodane diterpenoids by employing the common ABDE-tetracyclic intermediate 1. Herein, we report a new strategy for constructing isoryanodane ABCDE-ring structure 3 from 1 via a combination of the oxy-Cope rearrangement and SmI2-mediated transannular cyclization. 相似文献
The gem-difluoroalkenes and related compounds have gained much attention from the organic synthetic community due to their widespread applications as versatile fluorinated building blocks for the synthesis of pharmaceuticals, agrochemicals and functional materials. In the past two decades, significant progress has been made to the development of efficient methods for the construction of gem-difluoroalkenes and useful reactions involving the cleavage of CF bond in gem-difluoroalkenes. In this Digest review, these advances in the synthesis and reaction chemistry of gem-difluoroalkenes are summarized, with special emphasis placed on novel synthetic applications of them in recent ten years. 相似文献
The carbonyl cobalt complex Cp*Co(CO)I2 catalyzes carbenoid Co alkylation of N-(pyrimidin-2-yl)indole with methyl 3,3,3-trifluoro-2-diazopropionate regioselectively giving 2-substituted indole, while the N,N’-ligated cations [CpCo(L)I]+ (L = bipy, phen) provide 3-substitution exclusively. The structure of [CpCo(phen)I]PF6 was investigated by X-ray diffraction.
