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《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2017,129(24):6862-6865
The development of a direct and highly stereoselective synthesis of 2,3,5‐substituted tetrahydrofurans has been accomplished through a combination of batch‐ and microchip‐MS‐experiments. This sequential transformation comprises a Lewis acid‐mediated reaction of bis(silyl) dienediolate 1 and a broad range of aldehydes, furnishing products with three new σ‐bonds and three stereogenic centers in a one‐pot process with typically good yields and excellent stereoselectivity. Key steps which have been elucidated primarily with microchip‐MS‐experiments include a vinylogous aldol reaction and a Prins‐type cyclization. Furthermore, a titanium BINOL complex is a powerful chiral catalyst for this process. The products were further converted into bi‐ and tricylic products by carbonyl–ene reactions, proceeding with excellent yields and diastereoselectivity. 相似文献
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A general stereoselective entry to racemic eremophilane and valencane sesquiterpenes, via a common key intermediate and using an intramolecular Diels-Alder reaction, is described. 相似文献
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Cerebrosterol (2 4S hydroxycholesterol,1)formedinsmallamountsinhumanandanimalbrain1fromcholes terolisimportantforcholesterolhomeostasisinthisorgan .Theexcesscholesterolisconvertedinto 2 4S hydroxy cholesterolbyauniquebrain specific 2 4S hydroxylase ,whichcouldber… 相似文献
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The racemic cis-anti-trans-steroids 9 to 11 have been synthesized in a highly stereoselective manner starting from 4-methoxybenzocyclobutene carboxylic acid via the key step 8 → 9 . (cf. Scheme 2). 相似文献
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A novel C 3-symmetric arsine was employed in the one-pot cyclopropanation of olefins with carbonyl-stabilized arsonium ylides formed in situ from phenacyl bromide in the presence of NaHCO3. This new arsine demonstrates good stereoselectivity and activity in the one-pot cyclopropanation of arylidenemalononitrile.
[Supplementary materials are available for this article. Go to the publisher's online edition of Synthetic Communications® for the following free supplemental resource(s): Full experimental and spectral details.] 相似文献
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Hiroya Takada Yoshiaki Nishibayashi Sanjay Kumar Srivastava Kouichi Ohe Sakae Uemura 《Phosphorus, sulfur, and silicon and the related elements》2013,188(1):629-632
Asymmetric intramolecular selenocyclisation of alkenoic acids, alkenols and alkenyl urethanes using chiral ferrocenylselenenyl cations proceeds smoothly to give the corresponding lactones, cyclic ethers and N-heterocyclic compounds, respectively, in moderate yields with very high diastereoselectivities. 相似文献
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A short and highly stereoselective synthesis of squalamine (1) was accomplished in 9 steps from easily available methyl chenodeoxycholanate (2). The advanced intermediate 7α,24R-dihydroxy-cholestan-3-one (9) was synthesized by using improved dehydrogenation of 4 followed by conjugate reduction and efficient asymmetric isopropylation of aldehyde 7 as key reactions. 相似文献
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(-)-Slaframinel,anindolizidincalkal()idisolatedtYomthcfungusR/7i~()c't())IicllegIInlinicolainl965',usuallyinItctsleguminouscattle1tcdsandisrcsponsiblcli>rexcessivesalivationintheanimals.Also,lshowsthep()tcntialityinthetreatmentofdiseasesinvolvingcholinergenicdysfunction,andevenhassomebcneficialeffcctsonruminantdigestivefunction.Muchattentionhasbecndevotedtoitssynthesis'sinccitsabs()lutcstere()chcmistrywasestablishedas(lS,6S,8aS)-l-acetoxy-6-an1in()-ind()lizidine'.Thefirstenantioselectiveto… 相似文献
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ABSTRACT Among the known non-symmetrical naturally occurring aminotrehaloses possessing antimicrobial activity, the stereoselective synthesis of α, α-linked D-glucosaminyl-D-glucoside as well as of D-glucosaminyl-D-mannoside has been reported.1 In contrast, the synthesis of the α, β-isomer composed of two 2-amino sugar units occurring in tunicamycin antibiotics 1 has not been studied to the same extent and is not readily obtainable in pure form. 相似文献
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Diego M. Monzn Juan Manuel Betancort Toms Martín Miguel ngel Ramírez Víctor S. Martín David Díaz Díaz 《Molecules (Basel, Switzerland)》2021,26(6)
Cyclic products can be obtained through the intramolecular version of the Nicholas reaction, which requires having the nucleophile connected to the alkyne unit. Here, we report the synthesis of 1-oxa-3-cyclooctynes starting from commercially available (1R,3S)-camphoric acid. The strategy is based on the initial preparation of propargylic alcohols, complexation of the triple bond with Co2(CO)8, and treatment with BF3·Et2O to induce an intramolecular Nicholas reaction with the free hydroxyl group as nucleophile. Finally, oxidative deprotection of the alkyne afforded the cyclooctynes in good yields. Notably, large-sized R substituents at the chiral center connected to the O atom were oriented in such a way that steric interactions were minimized in the cyclization, allowing the formation of cyclooctynes exclusively with (R) configuration, in good agreement with theoretical predictions. Moreover, preliminary studies demonstrated that these cyclooctynes were reactive in the presence of azides yielding substituted triazoles. 相似文献