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1.
An efficient procedure for the preparation of 1α-hydroxycholesterol 3-acetate 4 is described, which starts from cholesterol and involves as key steps transannular cyclization of the ten-membered ring ontaining (E)-3β-acetoxy-5,10-seco-1(10)-cholesten-5-one 1 to the oxetane derivative 1α,5-epoxy-5α-cholestan-3β-ol acetate 3, and opening of the four-membered ether ring in the latter compound. 1β-Hydroxycholesterol diacetate 9 was obtained by oxidation of 4 to the 1-oxo derivative 8, followed by metal hydride reduction and acetylation. 相似文献
2.
《Tetrahedron: Asymmetry》1998,9(16):2827-2831
The stereoselective acetylation of meso-2,3-bis(3,4-dimethoxybenzyl)butanediol by vinyl acetate in the presence of Candida antarctica lipase in benzene gave the corresponding (+)-(2S,3R) monoester (ee ≥98%). Transesterification of meso-2,3-bis(3,4-dimethoxybenzyl)butyl diacetate, in the presence of the same enzyme, by ethanol in benzene/isopropyl ether gave the corresponding (−)-(2R,3S) monoester (ee ≥98%). Both enantiomers of the known cis-2,3-bis(3,4-dimethoxybenzyl)butyrolactone were synthesized from these monoesters. 相似文献
3.
2-(tert-Butyl)-3,7-dehydrotropone (7-(tert-butyl)bicyclo[3.2.0]hepta-1(7),2,4-trien-6-one; 1 ) was found to dimerize reversibly to 2A by [2 + 4]-cycloaddition/cycloreversion reaction. The equilibrium lies on the side of the highly strained dimer 2A in the solid state, and on the side of the monomer 1 in solution. The [2 + 4]-reaction is fully perisite-, regio- and stereoselective. Above room temperature, 1 irreversibly formed a decarbonylated dimer 6 , probably via the intermediate 9A or 9B , which resulted either from a dimerisation of 1 by [4 + 6]-cycloaddition or from a sigmatropic rearrangement of the originally formed dimer 2A or 2B . Similary, the 6-bromo derivative 14 afforded the corresponding decarbonylated dimer 15 . Should the formation of 6 and 15 be due to a primary cycloaddition then that reaction is fully peri-, site- and regioselective. Mild LiAlH4-reduction of 6 and subsequent acetylation yielded the acetate 11 , the structure of which was established by an X-ray analysis. More vigorous LiAlH4-treatment also reduced the terminal fulvenoid double bond of 6 and acetylation of the crude product led to the acetated 12 and 13 . 相似文献
4.
A new aminoquercitol derivative was synthesized starting from 1,4-cyclohexadiene. Photooxygenation of cyclohexa-1,4-diene afforded anti-2,3-dioxabicyclo[2.2.2]oct-7-en-5-yl hydroperoxide as the main product. The formed hydroperoxy endoperoxide was reduced with LiAlH4 to produce anti-2,3-dioxabicyclo[2.2.2]oct-7-en-5-ol. Protection of alcohol with acetyl chloride followed by reduction of the endoperoxide with thiourea, and then palladium-catalyzed ionization/cyclization reaction gave an oxazolidinone derivative. Hydrolysis of the oxazolidinone ring and acetylation gave an amino compound. Oxidation of the double bond in the amino compound with OsO4 followed by acetylation gave the amino tetraacetate and removal of the acetate groups furnished the desired aminoquercitol whose exact configuration was determined by X-ray diffraction analysis. 相似文献
5.
Decahydronaphthalene-1,2,3,4,5,6,7-heptol, a new polycyclitol, was synthesized starting from p-benzoquinone. An endo selective Diels-Alder cycloaddition between p-benzoquinone and 1-acetoxybutadiene followed by stereoselective reduction with NaBH4/CeCl3·7H2O led to the formation of an allylic cis-diol. The formed diol was converted into its acetate with Ac2O/pyridine, in a transformation that required inert atmosphere conditions to suppress a competing aromatization. Controlled oxidation by OsO4 of two olefinic bonds followed by acetylation yielded the heptaacetate whose structure was established unequivocally via application of X-ray crystallographic methods. Removal of the acetate groups by NH3 provided the target heptol. In addition, the carbonic anhydrase inhibitory potency of the title compound was investigated and it was shown to be a potent inhibitor compared to the standard CA inhibitors. 相似文献
6.
4-[2-cyclopentenyl]-3-hydroxy [1] bonzopyran-2-one(3) was cyclised to the bicyclie coumar in-1,3-ethano-2-bromo-1,2-dihydro-3H-pyrano [2,3-c] [1] benzopyran-5-one (6) by a sequence of reactions viz. acetylation of 3, addition of bromine to cyclopenteny double bond and treating the resulting acetyldibromo compound (5) with 4% alcoholic KOH, Cyclisation of compound (3) with mercuric acetate in methanol gave condensed furan derivative 7 which on reductive demercuration with zinc borohydride in dimethoxyethane gave the 1,3-propano-1,2-dihydrofuro [2,3-c] [1] benzopyran-4-one, 8. Cyclisation of compound 2 with come. H2SO4 furnished a mixture of bicyclic derivative 9 ad furo coumarin derivative 8. 相似文献
7.
Aziridination of a variety of alkenes with N-substituted hydrazines mediated by iodobenzene diacetate under mild conditions (K2CO3, CH2Cl2) and ambient temperature were achieved in good to excellent yields (up to 99%), and conversions. The practicality and simplicity of this C-N bond formation protocol was exemplified by its application to the aziridination of cholesteryl acetate in a stereoselective manner. 相似文献
8.
Methyl-monomethoxy conduritol-B and methyl-dimethoxy conduritol-B were synthesized starting from 2-methylbenzo-1,4-quinone. Bromination of 2-methylbenzo-1,4-quinone was followed by the reduction of the carbonyl groups with NaBH4 to give a dioldibromo compound. Methyl-dimethoxy conduritol-B was synthesized from the reaction of the dioldibromo compound with CH3ONa, followed by acetylation with Ac2O-pyridine to obtain methyl-dimethoxy diacetate. On the other hand, acetylation of the methyl-dioldibromo compound followed by reaction with LiOH gave a monoepoxide compound stereoselectively. The reaction of the epoxide with H+/Ac2O afforded the monobromo triacetate. Controlled reaction of monobromo-triacetate with CH3ONa in MeOH furnished the desired new methyl-monomethoxy conduritol-B. The structures of all synthesized compounds were characterized by spectroscopic methods. 相似文献
9.
With the exception of 2-formylcyclohexanone, which yields the E-exo-enol acetate, the phase-transfer catalysed acetylation of 2-acylcyclohexanones produces the 1-acetoxycyclohexene derivatives as the major products. The 1-acetoxy derivative is also obtained in good yield from the acetylation of 2-methoxycarbonylcyclopentanone but, generally, acetylation of 2-acylcyclopentanones yields the E-exo-enol acetates. 2-Acetylcyclopentanone, however, produces not only the E- and Z-exo-enol acetates, but also the endo-enol acetate, in a ratio of ca 2:2:1. The exo and endo-enol acetates were distinguished by 13CNMR spectroscopy and use of LIS reagents confirmed the configurational assignments of the exo-isomers 相似文献
10.
An efficient synthetic strategy has been developed for the synthesis of the pentasaccharide repeating unit corresponding to the O-antigen of Escherichia coli O181. A one-pot, two step iterative glycosylation and [2?+?3] block glycosylation strategy have been adopted for the construction of the pentasaccharide derivative 2, which was then transformed into target compound 1 after a series of functional group transformations. Here H2SO4-silica has been used successfully as a promoter for all glycosylation reaction. The stereoselective outcomes of all glycosylation reactions were very good. The 2-acetamido-2,6-dideoxy-l-glucose (l-QuipNAc) building block was obtained from known carbohydrate l-rhamnose precursors. 相似文献
11.
The preparation of benzoheterocyclic carbaldehydes in the 2-amino-substituted benzothiazole, benzoxazole and benzimidazole series is described. Starting with the methyl-substituted 2-aminobenzoheterocycle, the nitrogen is protected as an N,N-diBoc derivative. Next, free radical halogenation of the methyl group with NBS/AIBN affords the N(Boc)2-protected benzylic dibromide which is directly used in the final step. A mild silver nitrite/dimethylsulfoxide-mediated conversion of the dibromide to the aldehyde functionality completes the process. 相似文献
12.
Two new oxazolidinone polycyclitols, 4,5,7,8,9-pentahydroxy-3-tosyldecahydronaphtho [2,1-d]oxazol-2(9bH)-one and 4,5,6,7,8-pentahydroxy-3-tosyldecahydronaphtho [2,1-d]oxazol-2(9bH)-one were synthesized starting from p-benzoquinone. An endo selective Diels–Alder cycloaddition between p-benzoquinone and 1-acetoxybutadiene followed by stereoselective reduction with NaBH4–CeCl3·7H2O led to the formation of an allylic cis-diol. The obtained diols were protected with p-TsNCO to yield bis-carbamates and then a palladium-catalyzed ionization/cyclization reaction produced two oxazolidinone derivatives. Oxidation of the two double bonds in either oxazolidinones with OsO4 followed by acetylation produced oxazolidinone-pentaacetates whose exact configurations were determined by X-ray diffraction analysis. Controlled removal of the acetate groups furnished the desired two new oxazolidinone polycyclitols. 相似文献
13.
In this study, the novel 4-(N,N′-dimethylamino)phenyl substituted lutetium(III) acetate phthalocyanine (2) and its quaternized derivative (3) were synthesized via a Suzuki-Miyaura coupling reaction between tetrakis(iodo) lutetium(III)acetate phthalocyanine (1) and 4-(N,N-dimethylamino)phenylboronic acid, and subsequent quaternization using dimethyl sulfate, respectively. The obtained phthalocyanine 3 exhibited excellent solubility in water which is important for photodynamic therapy applications. Photophysical properties such as fluorescence quantum yield and fluorescence lifetime, and photochemical properties such as singlet oxygen generation and photostability were investigated to determine their suitability for photodynamic therapy. The lutetium(III) phthalocyanines, especially quaternized derivative 3, showed promising properties as potential photosensitizers for the treatment of cancer, producing higher singlet oxygen (ΦΔ = 0.59) than motexafin lutetium (ΦΔ = 0.31) which is a clinically used lutetium texaphyrin photosensitizer. 相似文献
14.
Reaction of (2,3)-2,3-(cyclohexylidenedioxy)butanenitrile, derived from ethyl ()-lactate, with the magnesium enolate of t-butyl acetate gave the corresponding ()-β-amino acrylate derivative, which was transformed into N-benzoyl acosamine by acetylation, stereoselective hydrogenation, acidic hydrolysis, and ring-formation followed by reduction with diisobutylaluminium hydride. 相似文献
15.
G. Srinivas Rao Neela Sudhakar B. Venkateswara Rao S. Jeelani Basha 《Tetrahedron: Asymmetry》2010,21(16):1963-1970
The formal synthesis of 3-epi jaspine B was achieved by using a stereoselective intramolecular oxa-Michael addition. The diacetate derivative of 3-epi jaspine B was also synthesized. 相似文献
16.
Mario Hüttenhofer Frank Schaper Hans H. Brintzinger 《Angewandte Chemie (International ed. in English)》1998,37(16):2268-2270
A stereoselective reaction of Sn(NMe 2 ) 4 with the silyl-bridged bis(cyclopentadienyl) derivative 1 generates the novel spiro compound 2 , in which two C2-symmetric six-membered rings of opposite configuration are joined at a tin center: One ring is R,R-, and the other S,S-configured. Subsequent reaction with two equivalents of ZrCl4 affords, by stereoselective Sn/Zr exchange, exclusively the C2-symmetric isomer of the ansa-zirconocene rac- 3 . 相似文献
17.
A new phenolic terpene aldehyde, alliodorin (1a), has been isolated from Cordia alliodora and shown to be a derivative of geranylhydroquinone. Alliodorin diacetate was synthesized by geranylation of hydroquinone followed by acetylation and finally by oxidation with selenium dioxide, thus confirming the assigned structure. Several other compounds from the oxidation reaction were isolated and characterized. 相似文献
18.
Graham R. Underwood Brajeswar Paul M. Alice Becker 《Journal of heterocyclic chemistry》1976,13(6):1229-1232
Pyridoxol, protected by acetylation of the hydroxyl groups, has been converted to its N-oxide which upon reaction with perfluoroacetie anhydride yields a 2-nor-2-hydroxymethylpyridoxol derivative as an intermediate. This compound undergoes acyl migration from the 3-position. Protection of the pyridoxol hydroxyls by benzylalion followed by the same treatment yields the unrearranged α2-hydroxy derivative. This compound has been converted to a series of α2-substituted pyridoxols (X = -Cl, -Br, -OCOCH3, -OCH3, -OC2H5). 相似文献
19.
H. D. Hausen K. Sille J. Weidlein W. Schwarz 《Journal of organometallic chemistry》1978,160(2):411-419
Trimethylgallium reacts with acetic acid in a molar ratio yielding methylgallium diacetate, CH3Ga(OOCCH3)2? The structure is determined by vibrational spectroscopy and the crystal structure is described. Methylgallium diacetate crystallizes in the monoclinic space group P21/c with lattice constants a 776.5, b 1428.9, c 1406.3 pm, β 91.87° and eight formula units per cell. The monomers are linked together by acetate groups forming polymeric, waved layers. Besides the bridging acetate there are also “free” acetate groups coordinated at the distorted trigonal-bipyramidal coordinated Ga(1) atom. A second gallium atom Ga(2) is coordinated distorted tetrahedrally, the acetate groups bonded to Ga(2) being all bridging. The mean intermolecular distances are: GaC 194.6 pm, Ga(1)Oapical 215.3 pm, Ga(1)Oeq(bridge) 194.3 pm, Ga(1)Oeq(free) 187.3 pm, Ga(2)O 191.3 pm, CC 151.5 pm, CO 119.4 pm, CO 131.1 pm, CO 127.3 pm. 相似文献
20.
Wilson Cardona Sara Robledo Juan Murga Miguel Carda Fernando Echeverri 《Tetrahedron》2006,62(17):4086-4092
Several structural analogues of the polyketide passifloricin lactone were synthesized using asymmetric stereoselective allylations and ring-closing methateses as key reactions. These compounds were active in vitro against intracellular amastigotes of Leishmania panamensis (strain UA140), trophozoites of Plasmodium falciparum (strain NF54), and Mycobacterium tuberculosis (strain H37Rv). However, in spite of the significative antiparasitic activity of some synthetic analogues a high cytotoxicity was also observed. Based on these results a lactam derivative was also synthesized. This compound maintained a good level of activity with less toxicity. 相似文献