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1.
(±)-(4,5-anti)-4-Benzyloxy-5-hydroxy-(2E)-hexenoic acid 6 was subjected to δ-lactonization in the presence of 2,4,6-trichlorobenzoyl chloride and pyridine to give the α,β-unsaturated-δ-lactone congener (±)-7 (87% yield) accompanied by trans-cis isomerization. This δ-lactonization procedure was applied to the chiral synthesis of (+)-(4S,5R)-7 or (−)-(4R,5S)-7 from the chiral starting material (+)-(4S,5R)-6 or (−)-(4R,5S)-6. Deprotection of the benzyl group in (+)-(4S,5R)-7 or (−)-(4R,5S)-7 by the AlCl3/m-xylene system gave the natural osmundalactone (+)-(4S,5R)-5 or (−)-(4R,5S)-5 in good yield, respectively. Condensation of (−)-(4R,5S)-5 and tetraacetyl-β-d-glucosyltrichloroimidate 22 in the presence of BF3·Et2O afforded the condensation product (−)-8 (97% yield), which was identical to tetra-O-acetylosmundalin (−)-8 derived from natural osmundalin 9. 相似文献
2.
Alakesh Bisai 《Tetrahedron letters》2007,48(11):1907-1910
We have developed an efficient and a general approach to chiral 2-substituted N-tosylpiperidines starting from chiral α-substituted-N-tosylaziridines. Using this approach, we have synthesized (+)-coniine. The synthesis of chiral N-tosyl-2-piperidinylethanol 15 and ent-15, was achieved from l- and d-aspartic acids, respectively in few steps. Piperidine 15 was converted into 2-(2-hydroxysubstituted)piperidines of type 2 in optically active form. By applying this strategy, asymmetric syntheses of halosaline (R,R)-2a, (+)- and (−)-sedamine 2b, (+)- and (−)-allosedamine 2c, (+)- and (−)-sedridine 2d, (+)- and (−)-allosedridine 2e, (+)-tetraponerine T-3 3a, T-4 3c, T-7 3b, and T-8 3d have been achieved in high yields. These stereoisomers can be interconverted via Mitsunobu inversion in excellent yields. 相似文献
3.
Robert W. Baker Simon O. Rea Elisabeth M.C. Schenkelaars Angela Totaro 《Tetrahedron》2005,61(15):3733-3743
Racemic 1-(1′-isoquinolinyl)-2-naphthalenemethanol rac-12 was prepared through a ligand coupling reaction of racemic 1-(tert-butylsulfinyl)isoquinoline rac-7 with the 1-naphthyl Grignard reagent 10. Resolution of rac-12 was achieved through chromatographic separation of the Noe-lactol derivatives 14 and 15, providing (R)-(−)-12 of >99% ee and (S)-(+)-12 of 90% ee. The ligand coupling reaction of optically enriched sulfoxide (S)-(−)-7 (62% ee) with Grignard reagent 10 furnished rac-12, with the absence of stereoinduction resulting from competing rapid racemisation of the sulfoxide 7. Reaction of optically enriched (S)-(−)-7 with 2-methoxy-1-naphthylmagnesium bromide was also accompanied by racemisation of the sulfoxide 7, and furnished optically active (+)-1-(2′-methoxy-1′-naphthyl)isoquinoline (+)-3b in low enantiomeric purity (14% ee). The absolute configuration of (+)-3b was assigned as R using circular dichroism spectroscopy, correcting an earlier assignment based on the Bijvoet method, but in the absence of heavy atoms. Optically active 2-pyridyl sulfoxides were found not to undergo racemisation analogous to the 1-isoquinolinyl sulfoxide 7, with the ligand coupling reactions of (R)-(+)- and (S)-(−)-2-[(4′-methylphenyl)sulfinyl]-3-methylpyridines, (R)-(+)-17 and (S)-(−)-17, with 2-methoxy-1-naphthylmagnesium bromide providing (−)- and (+)-2-(2′-methoxy-1′-naphthyl)-3-methylpyridines, (−)-18 and (+)-18, in 53 and 60% ee, respectively. The free energy barriers to internal rotation in 3b and 18 have been determined, and the isoquinoline (R)-(−)-12 examined as a ligand in the enantioselectively catalysed addition of diethylzinc to benzaldehyde; (R)-(−)-12 was also converted to (R)-(−)-N,N-dimethyl-1-(1′-isoquinolinyl)-2-naphthalenemethanamine (R)-(−)-19, and this examined as a ligand in the enantioselective Pd-catalysed allylic substitution of 1,3-diphenylprop-2-enyl acetate with dimethyl malonate. 相似文献
4.
The preparation of (+)- and (−)-12 by resolution of (±)-12 with (R)-N-phenylpantolactam, (R)-13, is described. From (+)- and (−)-12 a series of chiral bisnoradamantane derivatives, whose chirality stems from substitution at the bridgehead positions, have been obtained in both enantiomeric forms. 相似文献
5.
Renata M. Oballa Rebekah Carson Susan Lait Jay A. Cadieux Joël Robichaud 《Tetrahedron》2005,61(11):2761-2766
Sesquiterpenoids (+)-trans-dracuncuflifoliol (1) and (+)-4-hydroxyoppositan-7-one (2) were prepared stereoselectively from enantiomerically pure (7aR)-7a-methyl-1,2,5,6,7,7a-hexahydro-4H-inden-4-one ((−)-6), whose synthesis was described herein. Conjugate addition of the organocopper (I) reagent 10 to (−)-6, followed by epimerization of the ring junction, generated 3 of the 4 contiguous chiral centers of both natural products. 相似文献
6.
Antonio J Moreno-VargasPierre Vogel 《Tetrahedron letters》2003,44(27):5069-5073
Enantiomerically pure 2,8-diazabicyclo[3.2.1]oct-2-ene derivatives (+)-5 and (−)-5 have been obtained from 2-azido-3-tosyl-7-azabicyclo[2.2.1]heptanes (+)-1 and (−)-2 and their enantiomers, by ring expansion under radical conditions. Compounds (+)-5 and (−)-5 were transformed into hemiaminals 9 ((3S,4R,5R)- and 10 ((3R,4S,5S)-5-(2-aminoethyl)-2,3,4-trihydroxypyrrolidine) that are good inhibitors of α-mannosidases. 相似文献
7.
Helically chiral azahexahelicene 3 was prepared in four steps using the Mizoroki-Heck coupling followed by classical oxidative photodehydrocyclisation. Resolution of this new chiral system was achieved through separation by HPLC providing (−)- and (+)-3 in high optical purity. The absolute configurations of (−)- and (+)-3 were assigned as M and P, respectively, by means of circular dichroism. Each of the hexacyclic systems (M)-(−)- and (P)-(+)-3 was reacted with boron tribromide to provide the corresponding helical pyridophenols in good yields. 相似文献
8.
The irradiation of the title compounds [(Z)-1] having (S)-(+)-sec-butyl, (−)-mentyl and related chiral auxiliaries in methanol and 1,2-dichloroethane containing 2-(diethylamino)ethanol afforded chiral auxiliary-substituted (4S,5S)-, (4R,5R)-, (4R,5S)- and (4S,5R)-4,5-dihydrooxazole derivatives (2) along with (E)-1. It was found that the photoinduced electron transfer-initiated cyclization of 1 gives either of the two diastereomers for cis-2 and trans-2 in diastereomeric excess whose value varies from 6% to 81% depending on solvent and chiral auxiliary. 相似文献
9.
A series of antimalarial chiral 1,2,4-trioxanes (1-8) were synthesised in high enantiomeric purities. Enantioselective addition of R2Zn reagent to 3-methyl-2-butenal catalysed by (+)-MIB or (−)-MIB yielded both the enantiomers of the chiral allylic alcohols 9-11 (90-98% ee), which were subjected to diastereoselective photooxygenation in the presence of tetraphenylporphine (TPP) to obtain (R,R)-threo- or (S,S)-threo-β-hydroperoxy alcohols (12-14). Reaction of β-hydroperoxy alcohols (12-14) with different cyclic ketones produced optically active trioxanes 1-8. 相似文献
10.
The concise synthesis of (8aR)-(−)-albaconol (1) from (8aR)-albicanol (2) obtained from the lipase-assisted asymmetric acetylation of rac-2, was achieved in 45% overall yield (eight steps). By comparison of the sign of specific rotation of between synthetic (8aR)-(−)-albaconol (1) and natural (+)-albaconol (1), the absolute structure of natural (+)-1 was determined to be 1R,2R,4aS,8aS configuration. 相似文献
11.
Nicolas Robert 《Tetrahedron》2007,63(18):3702-3706
A concise enantiopure synthesis of six monoterpenic alkaloids of the actinidine series possessing a cyclopenta[c]pyridine skeleton, (+)-deoxyrhexifoline (4), (+)-boschniakinic acid (5), (+)-boschniakine (6), (−)-plantagonine (7), (−)-indicaine (8) and (−)-tecostidine (9) is reported starting with the chiral precursor 3-bromo-5-((4R)-phenyloxazolin-2-yl)pyridine (10). It involves a C-4 regioselective connection of a butene appendice and an intramolecular 5-exo-trig Heck annulation sequence followed by hydrogenation of the exocyclic alkene. Mixture of (3R)- and (3S)-7-((4R)-phenyloxazolin-2-yl)cyclopenta[c]pyridines was separated by HPLC before being transformed into enantiopure natural products (4-9) by modification of the oxazoline group. 相似文献
12.
Kenji Mori 《Tetrahedron letters》2007,48(32):5609-5611
Absolute configuration of gomadalactones A (1), B (2) and C (3), the pheromone components of the white-spotted longicorn beetle (Anoplophora malasiaca) was assigned as (1S,4R,5S)-1, (1R,4R,5R)-2 and (1S,4R,5S,8S)-3 by comparing their published CD spectra with those of (1R,5R)-(+)-4,4,8-trimethyl-3-oxabicyclo[3.3.0]oct-7-ene-2,6-dione (4) and (1S,5R,8S)-(+)-4,4,8-trimethyl-3-oxabicyclo[3.3.0]octane-2,6-dione (5) prepared from (R)-(−)-carvone (6). 相似文献
13.
Tetrahydroisoquinoline alkaloids, (S)-(−)-trolline, (R)-(+)-crispin A, and (R)-(+)-oleracein E, have been synthesized stereoselectively from the both enantiomers of common intermediate (S)-4 and (R)-4. The key step in the synthesis include a stereoselective Bi(OTf)3-catalyzed intramolecular 1,3-chirality transfer reaction of chiral non-racemic amino allylic alcohols (S)-6 and (R)-6 to construct both enantiomers of (E)-1-propenyl tetrahydroisoquinoline 4. 相似文献
14.
We have successfully synthesized enantiomerically pure (+)- and (−)-tert-butyl 6-cyano-3-[3-ethoxy-1,1,1-trifluoro-2-hydroxy-3-oxopropan-2-yl]-1H-indole-1-carboxylate (+)-1 and (−)-1, which are key intermediates of non-steroidal glucocorticoid receptor modulators, by employing a cinchona alkaloid catalyzed addition of 6-cyanoindole to ethyl trifluoropyruvate. The optimized method can be applied to large-scale synthesis. Furthermore, using the key intermediates (+)-1 and (−)-1, enantiomerically pure glucocorticoid receptor modulators (+)-3 and (−)-3 can be synthesized (>99% ee for both compounds). The glucocorticoid receptor binding affinity was influenced by the stereogenic center at the trifluoromethyl alcohol moiety; compound (−)-3 showed a higher binding affinity compared to (+)-3. 相似文献
15.
Toru TachiharaTakeshi Kitahara 《Tetrahedron》2003,59(10):1773-1780
Enantioselective total synthesis of (+)-epiepoformin 1, (+)-epiepoxydon 2 and (+)-bromoxone 3 using a chiral building block, ethyl (1R,2S)-5,5-ethylenedioxy-2-hydroxycyclo- hexanecarboxylate 6, is described. Since the synthesis afforded intermediates 18, 2 and 25, it accomplished a formal synthesis of (−)-theobroxide 19, (−)-phyllostine 22, (+)-herveynone 27 and (−)-asperpentyn 28. The usefulness of 6 for the synthesis of natural epoxycyclohexene derivatives was demonstrated. 相似文献
16.
Naga Venkata Sastry Mudiganti 《Tetrahedron letters》2008,49(49):6980-6983
Asymmetric synthesis of all the four stereoisomers of cis-3,4-dihydroxy-3,4-dihydromollugins 4 and 6 and trans-3,4-dihydroxy-3,4-dihydromollugins 5 and 7 was achieved. The O-methoxymethyl mollugin derivatives were dihydroxylated to (−)- and (+)-cis-3,4-dihydroxy-3,4-dihydromollugin derivatives using both AD-mix-α and AD-mix-β. Deprotection of the MOM-ethers of cis-dihydroxy compounds resulted in the targeted stereoisomers (−)-(3R,4R)-cis-3,4-dihydroxy-3,4-dihydromollugin 4, (−)-(3R,4S)-trans-3,4-dihydroxy-3,4-dihydromollugin 5, (+)-(3S,4S)-cis-3,4-dihydroxy-3,4-dihydromollugin 6 and (+)-(3S,4R)-trans-3,4-dihydroxy-3,4-dihydromollugin 7. These routes were paved with difficulties, for example, incompatibility of the substrates with AD-mixes, the unexpected formation of trans-dihydroxy compounds and failures in deprotection protocols. 相似文献
17.
Epimeric 3-carboxycyclopentylglycines (+)-10/(−)-10 and (+)-11/(−)-11 were efficiently prepared by the way of a sequence of Diels-Alder and retro-Claisen reactions. The synthesis incorporates a concise and inexpensive chemoenzymatic resolution of racemic compounds 4,5a, the N,O-protected derivatives of amino acids 10,11. Systematic screening with different enzymes and microorganisms was performed to select a very efficient catalyst for the separation of the racemic mixtures. The reaction conditions allowing deprotection of both ester and amino functions and to avoiding epimerization processes were studied. Enantiomers (i.e., (+)-10/(−)-10 and (+)-11/(−)-11) were obtained in high enantiopurity. The absolute configuration of all stereocenters was unequivocally assigned. 相似文献
18.
Palladium-catalyzed cyclization-methoxycarbonylation of (2R,3S)-3-methylpenta-4-yne-1,2-diol (6) derived from (2R,3S)-epoxy butanoate 7 followed by methylation gave the tetrahydro-2-furylidene acetate (−)-10, which was converted to the left-half aldehyde (+)-3. A Wittig reaction between (+)-4 and the phosphoranylide derived from the bithiazole-type phosphonium iodide 4 using lithium bis(trimethylsilyl)amide afforded the (+)-cystothiazole A (2). 相似文献
19.
(±)-Untenone A, one of the marine cyclopentanoids, has been conveniently synthesized via (±)-cis-1-hexadecylcyclopent-2-en-1,4-diol 9 which has been produced from 1-hexadecylcyclopenta-1,3-diene 6 via photo-oxidation and the following reduction. The key step of the present synthesis is the selective alkylation of cyclopenta-1,3-diene to form 6. Optically active (−)- and (+)-untenone A have been prepared from (−)- and (+)-9, respectively, after enzymatic kinetic resolution of (±)-9. 相似文献
20.
Luciane F. de Oliveira 《Tetrahedron letters》2006,47(21):3565-3567
We have described the synthesis of highly functionalized chiral cyclopentanoids, which are important building units for synthesis of biological active compounds. The (−)- or (+)-7,7-dimethoxy-1,4,5,6-tetrachlorobicyclo[2.2.1]hept-5-en-2-endo-yl acetate, obtained from the enzyme catalyzed transesterification of the racemate, was converted to α-diketone chiral. The α-diketone was treated with H2O2/NaOH and esterified with CH2N2 to furnish a mixture of the compounds (+)- or (−)-10 and (+)- or (−)-11. The reduction of the (+)- or (−)-10 and/or (+)- or (−)-11 with BH3·THF furnished the lactone (+)- or (−)-13 with excellent yield. The α-diketone was reduced with indium metal in the presence of NH4Cl furnishing the acyloin (+)-14 in 67% of yield. The treatment of acyloin (+)-14 with Pb(OAc)4 furnished the aldehyde (+)-15 with 80% of yield. The reduction of the aldehyde (+)-15 with NaBH4 has again produced the lactone (+)-13. 相似文献