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1.
《Tetrahedron》2003,59(48):9523-9536
The paper describes a new diastereoselective approach to oxygenated spongiane diterpenes functionally related to natural dorisenones. The strategy followed for the preparation of the spongiane framework, a B→AB→ABC→ABCD approach, is based on the preparation of epoxydecalone 11 (AB rings) from R-(−)-carvone, followed by an intramolecular Diels-Alder reaction for the construction of the C ring (compound 26). Further manipulation of the Diels-Alder adduct functionality allows the completion of the spongiane framework and the elaboration of several oxygenated spongiane-type compounds. The structures of two compounds 27 and 31, has been established by single-crystal X-ray crystallography.  相似文献   

2.
A convergent strategy toward the synthesis of lateriflorone (5) is described. Our approach is based on biosynthetic considerations and draws on a sequence of prenylation, oxygenation and Claisen reactions for the construction of chromenequinone 6, and a tandem Claisen/Diels-Alder reaction cascade for the synthesis of caged tricycle 7. Union of fragments 6 and 7 led to the synthesis of seco-lateriflorone (49).  相似文献   

3.
Reactions of C-(4-oxo-4H[1]benzopyran-3-yl)-N-phenyl nitrones (7) with allenic esters (8a-c) and allenic ketones (18a-d) furnish benzoindolizines (9a-k, 19a-d) in good yields. The formation of benzoindolizines is postulated to involve regioselective addition of 1,3-dipole to C2-C3 π bond of allenic esters/ketones followed by domino transformation of the cycloadducts, which involve an intramolecular aza Diels-Alder reaction in the intermediate C. DFT calculations of various parameters for diene and dienophile components in the proposed intermediate C have revealed that conformational constraints imposed by the alkyl groups (R=Me, Et) favor intramolecular aza-Diels-Alder cycloaddition. An alternative domino route to benzoindolizines (9a,d,g) involving sequential one-pot cycloaddition of azadienes (22a-c) with silyl-enol ether (23) followed by palladium(0)-catalyzed Heck coupling reaction has also been developed. Both these approaches represent novel domino routes for the synthesis of benzoindolizines.  相似文献   

4.
The second generation synthesis of (+)-pseudodeflectusin (1), a potential antitumor agent, has been achieved. The key synthetic step is the cascade reaction involving Diels-Alder reaction, lactonization, and decarboxylation to give cycloadduct 6 with complete regioselectivity in good yield. We found that NaH is the best base to facilitate the Diels-Alder reaction of hydroxypyrone 7 with alkyne 8. The present synthetic route enables the total synthesis of (+)-1 in only five-steps from the known compounds 7 and 8.  相似文献   

5.
The synthesis and reactions of several α,β-unsaturated chloromethyl sulfones is presented, for example [(chloromethyl)sulfonyl]-1,3-propadiene (4), [(chloromethyl)sulfonyl]ethene (5), [(dichloromethyl)sulfonyl]ethene (6) and (E,Z)-1,2-bis[(chloromethyl)sulfonyl]ethene (7). These compounds serve as ‘prepackaged’ Ramberg-Bäcklund reagents, which following an appropriate first step, such as Diels-Alder addition, react with base giving Ramberg-Bäcklund products.  相似文献   

6.
The transannular Diels-Alder (TADA) reaction was applied to the synthesis of the CDE ring system of nakiterpiosin (1). Tetracyclic compound 25 may be a key intermediate in the total synthesis of 1.  相似文献   

7.
A novel route for the total synthesis of lycopene 1 is described. The synthesis is based on: (i) a condensation between 4,4-dimethoxy-3-methylbutanal 4 and methylenebisphosphonic acid tetraethyl ester 5, leading to the C6-phosphonate 6, followed by (ii) a modified Wittig-Horner reaction between 6 and 6-methyl-5-hepten-2-one 7 producing dimethoxy-3,5,9-triene 8, and (iii) another modified Wittig-Horner reaction between C15-phosphonate 2 and C10-triene dialdehyde 3 producing all-E-lycopene. The synthetic steps are easily operated and practical for the large-scale production.  相似文献   

8.
A concise synthesis of novel cardiac glycoside analogues of rhodexin A, 14 and 24, having the BCD tricyclic system is described. The key constructive step is an inverse-electron demand Diels-Alder reaction of the silyl enol ether 4 and the 2-acetyldiene, 7 and 15.  相似文献   

9.
Antonio Abad 《Tetrahedron》2007,63(7):1664-1679
A diastereoselective approach to polyoxygenated atisene-type diterpenes starting from (S)-(+)-carvone is described. The key steps used in the preparation of the atisene framework are an intramolecular Diels-Alder reaction, an intramolecular diazoketone cyclopropanation, an endocyclic cyclopropane ring cleavage and the regioselective reduction of an allylic bromide by a low-valent chromium species. The synthesis of natural atisanes antiquorin (1), atis-16-ene-3,14-dione (3), atis-16-ene-2,3,14-trione (8) and 3β-hydroxy-atis-16-ene-2,14-dione (9) following this approach is presented. Also described is the synthesis of 18-hydroxy-atis-16-ene-3,14-dione (5), the structure erroneously assigned to an atisene isolated from the Fijian plant Euphorbia fidjiana. This work shows that the natural atisene isolated from this plant is, in fact, the epimer at C-4 of this compound.  相似文献   

10.
The first total synthesis of the alkaloid fumaridine 1a is reported. The key step is the assemblage of the arylmethylene isoindolinone 2a (E) by Horner reaction between the phosphorylated isoindolinone 3a and the suitably substituted benzaldehyde 4. N-Lactam deprotection and concomitant EZ isomerization complete the synthesis of the title compound.  相似文献   

11.
Three 9-substituted anthracene derivatives, that is, 9-hydroxymethylanthracene (2), 9-methoxymethylanthracene (3) and bis(9-anthrylmethyl) adipate (6), were chosen as the model compounds to evaluate the reactivity in their Diels-Alder reactions with [60]fullerene and in retro Diels-Alder reactions of the formed cycloadducts. Corresponding adducts 4, 5 and 7 were prepared in high yields under solvent-free conditions using high-speed vibration milling technique. In order to determine thermal stabilities of adducts 4, 5 and 7, their dissociations in the temperature range of 40-65 °C were investigated. Fitting the dissociation rates and temperatures to the Arrhenius equation gives the activation energies of 25.8, 21.8 and 24.9 kcal/mol for compounds 4, 5 and 7, respectively.  相似文献   

12.
The synthesis of conformationally strained 2,2′-bipyridine thiamacrocycles 5, 6, 9, 10 and their chiral sulfoxides 11-14 is elaborated using, (1) homo-coupling of 1,2,4-triazine sulfide 3 with potassium cyanide and (2) Diels-Alder/retro Diels-Alder (DA-rDA) with 2,5-norbornadiene or 1-pyrrolidino-1-cyclopentene as the key steps. The crystal structure determinations of 4-6 and the theoretical calculations at DFT/B3LYP/6-311G∗∗ level were conducted thus establishing conformational preferences of the target thiamacrocycles  相似文献   

13.
Construction of the tricyclic derivative 5, a common intermediate for the synthesis of sesquiterpenoids 1-4, was accomplished by using the intramolecular Diels-Alder reaction. Availability of 5 was demonstrated by effective total synthesis of chiloscyphone 1 and isochiloscyphone 2.  相似文献   

14.
A new route to thiacrown ethers 5a-d and 6a-d incorporating a 2,2′-bipyridine subunit is elaborated using, (1) homo-coupling of 1,2,4-triazine sulfides 3a-d tethered to poly(ethylene glycol) chains with potassium cyanide and (2) Diels-Alder/retro Diels-Alder reaction with norbornadiene or 1-pyrrolidino-1-cyclopentene as the key steps.  相似文献   

15.
The total synthesis of an H-type blood group determinant in a model biological setting is described. The construct is comprised of a high mannose core structure with projecting lactose spacers, culminating in a two-copy presentation of the H-type blood group determinant itself. Key reactions that were used in this construction include sulfonamidohydroxylation (see 1518) and benzoate-directed glycosylation via an activated thiophenyl donor (see 3436). Another key strategic element involved the epimerization of an interior core glucoside to reach the β-mannoside (see 3738) required in the ring C sugar of the high mannose core.  相似文献   

16.
Using sulfolenopyrroles (4) and (11) methods are developed for the synthesis of opp- (15,18,19) and adj- (25) bis-sulfolenoporphyrins; such compounds are useful building blocks for the refunctionalization of the porphyrin system, and readily undergo Diels-Alder cycloaddition reactions.  相似文献   

17.
Masashi Ohba  Itaru Natsutani 《Tetrahedron》2007,63(41):10337-10344
A full account of the highly stereoselective total synthesis of two indole alkaloids, suaveoline (4) and norsuaveoline (5), is presented. Central features of the synthetic strategy include the conversion of l-tryptophan methyl ester (12) into the oxazole derivative 11 and the intramolecular Diels-Alder reaction of the oxazole-olefin 19 leading to the pentacyclic pyridine derivative 21.  相似文献   

18.
The thermal reaction of phencyclone (2) with a 1:1 mixture of 1,8-pyrenequinone (4) and 1,6-pyrenequinone (5) yields 2:1 adducts only of compounds 2 and 4. The observed polycyclic aromatic hydrocarbon 8 is formed via double Diels-Alder addition of 2 to 4, and the polycyclic ketone 9 arises from a combination of Diels-Alder and hetero-Diels-Alder reactions of 2 and 4. In contrast, Lewis acid-catalyzed reactions of 2, 4, and 5 give 2:1 adducts only of 2 and 5. The chief product, polycyclic diketone 10, is derived from a double hetero-Diels-Alder addition of 2 to 5. X-ray analysis of compound 8 shows it to be an exceptionally large polycyclic aromatic arch, and the X-ray structure of 10 reveals it to be a chiral molecular tweezer.  相似文献   

19.
Intramolecular ionic Diels-Alder reaction of 2-methyl-3,9,11-tridecatriene-2-ol (1) was studied under acidic conditions. Treatment of 2-methyl-3,9,11-tridecatriene-2-ol (1) with trifluoromethanesulfonic acid yielded 7-methyl-8-isopropenyl-1,2,3,4,4aR,7R,8R,8aS-octahydronaphthalene (4) and (1Z)-1-((E)-but-2-enylidene)-2-(2-methylpropenyl)cyclohexane (5) through regioselective intramolecular ionic Diels-Alder reaction. The reaction appeared to proceed partly through a stepwise mechanism involving a carbocation intermediate. However, a concerted pathway rather than a stepwise one is suggested to be involved in the acid-catalyzed intramolecular Diels-Alder reaction of 2,11-dimethyl-1,3,9,11-dodecatetraene (13).  相似文献   

20.
Shigella flexneri serotypes 6 and 6a are closely related bacteria causing shigellosis in humans. Their O-antigens are {→4)-β-d-GalpA-(1→3)-β-d-GalpNAc-(1→2)-[3Ac/4Ac]-α-l-Rhap-(1→2)-α-l-Rhap-(1→}n acidic polysaccharides ({ABAcCD}n), which only differ in the degree of O-acetylation. A concise synthesis of two disaccharides (BC, BAcC) and four trisaccharides, representing portions and/or analogs of the O-antigens, is described. A protected intermediate compatible with late stage 3C-O-acetylation, and/or galactosyl () to galacturonic acid (A) conversion, was designed and assembled from trichloroacetimidate and thioglycoside donors tuned for high yielding glycosylation and excellent stereocontrol. The galacturonic moiety was efficiently introduced from galactose using a TEMPO/NaOCl/NaClO2-based oxidation protocol optimized for full compatibility with sensitive moieties, such as allyl ethers and acetates. Final Pd/C-mediated deprotection provided the targets, including the propyl glycoside ABAcC, its non O-acetylated counterpart ABC, and the non acidic analogs A°BAcC and A°BC. The BC and ABC oligosaccharides are also portions of the O-antigen from Escherichia coli O147, which causes diarrhea in pigs.  相似文献   

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