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1.
《Tetrahedron letters》1988,29(42):5417-5418
New conditions for effective cleavage of SEM ethers were developed (TBAF/HMPA in the presence of MS 4A) and usefulness of this reaction was demonstrated by the synthesis of thyrsiferyl-23 acetate. 相似文献
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Roger W. Binkley 《Journal of carbohydrate chemistry》2013,32(2):227-242
Methyl α-D-mannopyranoside (4) was converted into methyl 2,6-dideoxy-3-C-methyl-ct-D-ribo-hexopyranoside (20) (methyl α-D-mycaroside) by an efficient sequence of reactions (Schemes 1 and 3). A similar set of reactions also was used to convert L-rhamnose (2) into methyl α-L-mycaroside (21). Attempted synthesis of methyl 2,6-diseoxy-3-C-methyl-a-D-arabino-hexopyranoside (22) (methyl α-D-olivomycosidej from methyl 6-deoxy-3-C-methyl-4-O-(2,2-dimethylpropanoyl)~2-O-trif lyl-α-D-arabino-hexopyranoside (18), a compound generated during~synthesis of 20, was thwarted by a methyl migration which produced methyl 2,6-dideoxy-2-C-methyl-α-D-ribo-hexopyranoside (23). 相似文献
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[reaction: see text] Cochleamycin A (1) was synthesized in 2.4% overall yield via a 23-step linear sequence starting from 3-butene-1-ol. Key features of the synthesis include the synthesis of (Z)-1,3-diene 21 via a Stille coupling of 4 and 5 and a transannular Diels-Alder reaction of macrocycle 26 to provide the complete carbon skeleton of 1. 相似文献
5.
Haack T Haack K Diederich WE Blackman B Roy S Pusuluri S Georg GI 《The Journal of organic chemistry》2005,70(19):7592-7604
[reaction: see text] Two formal total syntheses of the (-)-salicylihalamides, based on chiral pool approaches, are reported. D-glucose and L-rhamnose were used to prepare advanced intermediates 23 and 54, which can be converted in three or four steps, respectively, to the target compounds. The synthesis of 23 from a known D-glucose-derivative was accomplished in 12 steps and 17% overall yield, and the synthesis of 54 from a known L-rhamnose-derivative was done in nine steps and 6% overall yield. A key step in the synthesis was a ring-closing metathesis reaction to prepare the macrocyclic ring system. It was demonstrated that the phenolic protecting group was critical for inducing the preferential formation of the desired E isomer. It was further shown that the protecting group at the C13 hydroxyl group had no significant influence on the E:Z ratio during the ring-closing metathesis reaction. 相似文献
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A highly convergent and efficient total synthesis of the potent antitumor polyketide (-)-callystatin A is described. The synthesis required 19 steps from N-propionyl oxazolidinone 23 and produced the desired product in 3.5% overall yield. 相似文献
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The total synthesis of (+)-nakadomarin A is described. A three-component cycloaddition of a hydroxylamine, aldehyde, and cyclopropane to form a highly functionalized tetrahydro-1,2-oxazine serves as the foundation for this synthesis. The resulting oxazine is formed as a single diastereomer with the absolute configuration being dictated by the chirality of the cyclopropane. Other key steps include: desymmetrization of a malonate by reduction, Heck cyclization and pyrrolidine formation, and ring-closing metathesis to form both cycloalkenes. Overall, the synthesis required 23 linear steps from the cyclopropane, which in turn is available (six steps) in optically pure form from commercially available d-mannitol. 相似文献
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A literature survey indicated that stereospecific non-reductive β-face methylation at C(10) of steroidal synthesis intermediate BCD-tricyclic 9-en-5-ones had never been effected. An attempt to define the factors controlling the β/α product ratio in such alkylations was made. The course of methylation is significantly affected by the temperature. In the best case, methylation of the sodium enolate of 17 β-t-butoxy-19-(3,5-dimethyl-4-isoxazolyl)-deA-androst-9-en-5-one ( 18 ) in tetrahydrofuran at ? 78° gave a β/α product ratio of > 5:1. The reaction mixture contained no unalkylated or dialkylated materials, indicating that enolate exchange probably did not occur at this temperature. The 10β-methylated product 23 , isolated in 78% yield, was converted to Δ9(ll)-dehydrotestosterone ( 29 ). Compounds 23 and 29 are potential intermediates for the synthesis of 11-oxygenated steroids. 相似文献
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A combined use of alpha-lithiation and nucleophilic substitutions of N,N-dimethyl 3,4-bis(trimethylsilyl)-1H-pyrrole-1-sulfonamide 8c led to several 2-substituted 3, 4-bis(trimethylsilyl)-1H-pyrrole-1-sulfonamides. Utilizing the beta-effect of a trimethylsilyl group, a highly regioselective synthesis of 2,3,4-trisubstituted 1H-pyrroles 23 and 34 was accomplished. The marine natural product lukianol A (3) was prepared utilizing this strategy. 相似文献
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A practical synthesis of triquinacene-2-carboxylic acid 1 from the readily available Thiele's acid 2 is reported. Optically active 2-formamidotriquinacene 20 derived from (+)-1 was condensed with the acid chloride of (+)-1 to give the secondary amide 23 via 22. Compound 23 was then converted into the cyclic imidate salt 26 with the hope to eventually achieve the synthesis of the dodecahedrane nucleus (see 28). 相似文献
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Fluoro-homoneplanocin A (4) was synthesized from d-ribose, via the enyne ring-closing metathesis of 9, the stereoselective opening of epoxide 23a with fluoride, and a simultaneous oxidation-elimination reaction. The key intermediate 8 is expected to serve as a versatile intermediate for the synthesis of carbanucleosides. 相似文献
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Synthesis of a Nickel(II) B,C,D-Hexadehydrocorrinate by (A→D)-Ring Closure The B,C,D-hexadehydrocorrin of type 10 fills a gap in the corrin family whose members can occur at different oxidation levels. We report here on the synthesis of a correspondingly protected secocorrin 23 and its convenient cyclization to 10 相似文献
13.
The synthesis of two naphthoquinone antibiotics, dehydroherbarin (7) and 6-deoxybostrycoidin (5), was accomplished by reaction of 3-acetonyl-2-bromomethyl-6,8-dimethoxy-1,4-naphthoquinone (23) with either triethylamine or ammonia, respectively. This is the first report on their synthesis. 相似文献
14.
A highly stereoselective synthesis of the C10-C23 fragment of (-)-dictyostatin has been achieved using a Carreira alkynylation and a Marshall-Tamaru allenylzinc addition as key steps. 相似文献
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Kumemura T Choshi T Hirata A Sera M Takahashi Y Nobuhiro J Hibino S 《Chemical & pharmaceutical bulletin》2005,53(4):393-397
A total synthesis of a new furo[3,2-h]isoquinoline alkaloid TMC120-B (2), isolated from Aspergillus ustus together with two related compounds, has been completed in sixteen steps. The key step is the synthesis of the appropriate 3,7,8-trisubstituted isoquinoline framework (23) based on a thermal electrocyclic reaction of the 1-aza 6pi-electron system involving the benzene double bond. In addition, the microwave assisted electrocyclic reaction of this system was newly performed. 相似文献
16.
A short synthesis of (+/-)-deoxypenostatin A (28) has been carried out using the convergent coupling of dienal 11, epoxide 13, and methylenetriphenylphosphorane (17) to prepare trienol 19 in only two steps. The key step is the Yb(OTf)(3)-catalyzed intramolecular Diels-Alder reaction of hydrated trienyl glyoxylate 23, which gives lactone 24 stereoselectively. Elaboration of lactone 24 to enone 27 by an intramolecular Horner-Emmons Wittig reaction and epimerization completes the synthesis of 28. Modest yields of Diels-Alder adducts 45a and 46a could be prepared analogously from MEM ether 44c, but the sensitivity of several of the intermediates precluded the elaboration of 45a to penostatin A (1). 相似文献
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[structure: see text] By relying on the asymmetric aldol reactions of chiral ketones, a highly stereocontrolled synthesis of each of the C(17)-C(22) and C(23)-C(35) degradation fragments of reidispongiolide A has been achieved. This permits a configurational assignment of the complete C(17)-C(36) region of this antimitotic macrolide, along with providing advanced intermediates for a projected total synthesis. 相似文献
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[reaction: see text] During studies directed toward the total synthesis of garsubellin A, a concise stereocontrolled synthesis of the 18-epi-tricyclic compound 3 was achieved. Key steps were a one-pot stereoselective construction of the bicyclic lactone 23 followed by a formal migration to the bicyclo[3.3.1]nonane-1,3,5-trione and an intramolecular Wacker-type tetrahydrofuran ring formation. 相似文献