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1.
New, short, and flexible procedures have been developed for syntheses of steroid and D-homo steroid skeletons. A Mukaiyama reaction between the silyl enol ether of 6-methoxytetralone and 2-methyl-2-cyclopentenone or carvone, with transfer of the silyl group to the receiving enone, gave a second silyl enol ether. Addition of a carbocation, generated under Lewis acid conditions from 3-methoxy-2-butenol, 3-ethoxy-3-phenyl-2-propenol or 3-methoxy-2-propenol to this second silyl enol ether gave adducts, which could not be cyclized by aldol condensation to (D-homo) steroid skeletons. The Mukaiyama-Michael reaction of the silyl enol ether of 6-methoxy tetralone with 2-methyl-2-cylopentenone gave a second silyl enol ether, which reacted in high yield with a carbocation generated from 3-hydroxy-3-(4-methoxyphenyl)propene. Ozonolysis of the double bond in this adduct gave a tricarbonyl compound (Zieglers triketone), which has been used before in the synthesis of 9,11-dehydroestrone methyl ether. A second synthesis of C17 substituted CD-trans coupled (D-homo) steroid skeletons has been developed via addition of a carbocation, generated with ZnBr2 from a Torgov reagent, to a silyl enol ether containing ring D precursor. The obtained seco steroids have been cyclized under formation of the 8-14 bond by treatment with acid. The double bonds in one of the cyclized products have been reduced to a C17-substituted all trans steroid skeleton. 相似文献
2.
《Tetrahedron: Asymmetry》2006,17(6):892-899
Enantiomerically pure 2-alkylidenetetrahydrofurans have been prepared by TiCl4 mediated enantiospecific reactions of 1,3-bis-silyl enol ethers with enantiomerically pure epichlorohydrin. In addition, the enzymatic kinetic resolution of 2-alkylidenetetrahydrofurans, using Candida antarctica lipase B (CAL-B), was studied. Enzymatic kinetic resolution of monocyclic 5-vinyl-2-alkylidenetetrahydrofuran with CAL-B afforded the enantiomerically pure ester with 97% ee. For a bicyclic 2-alkylidenetetrahydrofuran, this proceeded with excellent enantioselectivity (E >100) affording the enantiomerically pure acid with 98% ee. 2-Alkylidenetetrahydrofurans were prepared by [3+2] cyclization reactions of 1,3-dicarbonyl dianions (‘free dianions’) or 1,3-bis-silyl enol ethers (‘masked dianions’). 相似文献
3.
Kaylene M. Pritchard 《合成通讯》2013,43(23):4076-4096
We now report the first reaction of Ph3P(SCN)2 with 4,6-dihydroxy-5-methylisophthalic acid to give 10-methyl-2,8-dithio-1,3-oxazino-1,3-benzoxazine-4,6-dione. Also, the enol tautomer has been utilized in the reaction of β-keto acids with Ph3P(SCN)2 to give novel 2-thio-1,3-oxazines. Subsequent reaction of the 2-thio-1,3-oxazines with benzylamine resulted in opening of the oxazine ring and gave novel dibenzylamino-enamides, which could be cyclized to thiouracils. The reaction of 2-thio-1,3-oxazines with morpholine at low temperature led to the production of unstable 2-Mercapto-2-morpholino-1,3-oxazines. 2-Mercapto-2-morpholin-4-yl-2,3,5,6,7,8-hexahydro-4H-1,3-benzoxazin-4-one was observed to lose H2S at room temperature to give 2-morpholin-4-yl-5,6,7,8-tetrahydro-4H-1,3-benzoxazin-4-one, which was subsequently tested and found to exhibit some antiplatelet activity. 相似文献
4.
由内酯2和Tebbe试剂反应合成了双环烯醚化合物5-苄氧基-2,8-二亚甲基-3,4,9,10-四氢-2H,8H-苯并[1,2-b; 3,4-b']二吡喃(3), 环烯醚在酸性条件下很容易水解和异构化, 在酸存在下外环烯醚3于10 min内转化为内环烯醚4, 较长的反应时间只能得到水解物或其它分解产物. 相似文献
5.
Zhihong Wu Charles U. Pittman 《Journal of polymer science. Part A, Polymer chemistry》1998,36(6):873-881
BF3·OEt2-initiated polymerizations of 2-methylene-1,3-dioxepane gave polymers composed of both ring-retained and ring-opened structures. The ring-opening content increased with an increase in polymerization temperature. Poly(4,7-dimethyl-2-methylene-1,3-dioxepane) propagated slower during BF3·OEt2-initiated polymerization and had a lower ring-opened content than poly(2-methylene-1,3-dioxepane). The type of acid initiator used also affected the amount of ring opening observed. Stronger acids gave less ring opening. Attempted BF3·OEt2-initiated copolymerizations of these seven-membered ring cyclic ketene acetals with isobutyl vinyl ether at room temperature resulted in formation of the two homopolymers. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 873–881, 1998 相似文献
6.
Tonghaosu and its analogs are a class of structurally interesting spiroketal enol‐ether compounds. A practical route to furandiol, a key intermediate for their syntheses, was developed. Using Friedel‐Crafts benzoylation of 3‐(2‐fury I) propyl acetate, a diarylketone was obtained in high yield, which was further transformed into corresponding furandiol by reduction with NaBH4 in basic medium with simultaneous ester hydrolysis. The furandiol was then cyclized into the desired spiroketal enol‐ether compound in the presence of CuSO4 5H2O. 相似文献
7.
Base-catalyzed rearrangements of both individual 4-(acylmethylidene)butenolides and their mixtures prepared by condensation
of citraconic anhydride with various phosphoranes occur successfully only in the presence of 5.2% MeONa in MeOH (molar ratio
MeONa: substrate ≤ 10: 1, room temperature, 1–2 h). Under these conditions, the yields of 2-cinnamoyl-4-methylcyclopent-4-ene-1,3-dione
(coruscanone B) and 2-acetyl-4-methylcyclopent-4-ene-1,3-dione are 56 and 65%, respectively. With a considerable increase
in the reaction temperature or the molar ratio MeONa: substrate, formal addition of MeOH to the C(4)=C(5) double bond of these
triketones becomes an appreciable (or predominant) process. A reaction of coruscanone B with CH2N2 in ether gives coruscanone A as a ~3: 2 mixture of (Z)- and (E)-methyl enolates (43%); other products (10%) result from the expansion and aromatization of the five-membered ring of the
triketone. The simplest analog of coruscanone B, 2-acetyl-4-methylcyclopent-4-ene-1,3-dione, reacts with CH2N2 in a similar way. 相似文献
8.
N. A. Keiko E. A. Funtikova N. V. Vchislo L. I. Larina Yu. L. Frolov 《Russian Journal of Organic Chemistry》2011,47(12):1832-1840
2-(1-Alkoxyvinyl)-1,3-thiazolidines reacted with H2O or D2O in the presence of 105 mol % of p-toluenesulfonic acid or trifluoroacetic acid (20°C, 1 h) to give 2-acetyl-1,3-thiazolidine in quantitative yield. 2-(1-Alkoxyvinyl)-3,5-diphenylimidazolidines
underwent hydrolysis in the presence of 20 mol % of an acid (20°C, 24 h) at the vinyloxy group with high regioselectivity
yielding 2-acetylimidazolidines. Hydrolysis of 2-(1-alkoxyvinyl)-3-phenyl-1,3-oxazolidines in the presence of 10 mol % of
p-toluenesulfonic acid (20°C, 5 days) takes two pathways, one of which involves the endocyclic C-O bond with ring opening and
the other involves the vinyloxy group to produce 2-acetyl-3-phenyl-1,3-oxazolidine. Unlike phenyl-substituted 1,3-thiazolidines
and imidazolidines, hydrolysis of their 3-methyl- and 3,5-dimethyl-substituted analogs in acid medium occurs mainly via ring
opening. The observed hydrolysis pathways were interpreted in terms of B3PW91/6-311G(d,p) quantum-chemical calculations. 相似文献
9.
《Tetrahedron》1987,43(4):765-770
The conversion of γ-substituted enol ethers to conjugated cyclopropyl ketones which are part of the skeleton of pleuromutilin is described. The nucleophilic opening of the cyclopropane ring is shown to proceed in a highly stereospecific manner. The cyclopropane bond which is cleaved (C8-C4) is the one exhibiting the maximum overlap with the π-orbital of the carbonyl group. This reaction offers a convenient method for the stereospecific introduction of an equatorial fluorine at C8. 相似文献
10.
M. Laguerre J. Dunogues N. Duffaut R. Calas 《Journal of organometallic chemistry》1976,120(3):319-328
Methyl or trimethylsilyl ether derivatives of mono- or di-phenols easily undergo disilylation to give disilylated enol ethers or bis(enoxysilanes) with a 1,4-cyclohexadienic ring which are new classes of intermediates in synthesis. In the case of monophenol derivatives hydrolysis affords stable δ-silyl-β,γ-unsaturated ketones, which are converted to the corresponding conjugated cyclohexenones by desilylation (e.g. 4-allyl-2-cyclohexenone which was previously difficult to prepare). In the case of diphenol derivatives cyclohexanediones are obtained upon hydrolysis. Polysilylation occurs with methyl phenyl thio ether, pyrocatechol and even with o-cresol derivatives, to give new products. 相似文献
11.
Gimalova F. A. Sadretdinov I. F. Spirikhin L. V. Miftakhov M. S. 《Russian Journal of Organic Chemistry》2003,39(9):1234-1239
Deprotonation of 1-[(1S,3R)-2,2-dimethyl-3-(2-methoxymethyloxyethyl)cyclopropyl]-2-propanone with lithium diisopropylamide in THF at -78°C and subsequent treatment of the resulting enolate with Me3SiCl yielded mainly the corresponding terminal silyl enol ether. The condensation of intermediate enolate with benzaldehyde regioselectively afforded a mixture of the corresponding aldol and its dehydration product. The reactions of the title ketone with NBS, as well as of the silyl enol ethers derived therefrom with I2, led to formation of mixtures of products via opening of the cyclopropane ring. 相似文献
12.
Lakshmi V.R. Babu Syamala Trimbak B. Mete Ramakrishna G. Bhat 《Tetrahedron letters》2018,59(34):3288-3291
FeCl3·6H2O/triethylsilane composite catalyst system is successfully developed for the selective conjugate reduction of carbon-carbon double bond of Michael acceptor-alkylidene-β-keto esters and alkylidene-1,3-diketones under mild reaction conditions to afford the corresponding saturated β-keto esters and 1,3-diketones. The process involves the iron-catalyzed hydrosilylation, followed by in situ hydrolysis of silyl enol ether. The optimal reaction conditions include 20?mol% of FeCl3·6H2O and triethylsilane in dichloromethane at room temperature. A broad range of substrates undergoes the reduction in 1, 4-selective manner to afford the corresponding saturated compounds in excellent yields. 相似文献
13.
Upon irradiation, cyclic enol ethers such as 1-methoxy-cyclopentene (4) mainly add across the cyano group of benzonitrile (1), under formation of 2-azabutadienes of an imidoester type. This is in agreement with the so-called Δ G-correlation which was reported earlier (ref. 5 and 6). 4-Phenyloxazole (9) is formed from 1 and 1,3-dioxole (5) probably by a similar photochemical process followed by electrocyclic ring opening and hydrolysis. The low yield of the latter photoreaction and the almost exergonic electron transfer between 5 and 1 may point to back electron transfer as the main energy wasting process. From 1 and 2,3-dihydrido-furan (2) only the ortho cycloadduct 6 has been isolated in low yields. 相似文献
14.
《Tetrahedron letters》1987,28(42):4943-4946
The bicyclo[3.2.1]octane ring system is assembled by a three-step process featuring a thermally induced [4+2] cycloaddition followed by a 1,3-benzodithiolium ion mediated cyclization onto an enol or silyl enol ether double bond. 相似文献
15.
The protected 5′-oxo-6,5′-cyclouridine 13 reacts with diazomethane to afford mostly the spiro-epoxide 18 (79%), but it also undergoes ring-expansion to give the corresponding 5′-oxo-6,6′-cyclonucleoside 16. Under the conditions of the reaction, ketone 16 reacts further with diazomethane to give the enol ether 20 (12% overall), the isomeric 4-methoxy nucleoside 15 (2%), and the spiro-epoxide 19 (4.4%). Acid hydrolysis of the enol ether 20 , followed by reduction of the resulting ketone with sodium borohydride, affords a separable mixture of the 5′S (L-talo) and 5′R (D-allo) methylene-bridged cyclonucleosides 7 and 8 , respectively. From proton nmr measurements, it appears that the 6′-methylene groups of these cyclonucleosides project towards the 2′,3′-edge of the furanose ring. 相似文献
16.
Dr. Christoph W. Wullschleger Prof. Dr. Jürg Gertsch Prof. Dr. Karl‐Heinz Altmann 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(39):13105-13111
The stereoselective syntheses of 7,8,9‐trideoxypeloruside A ( 4 ) and a monocyclic peloruside A analogue lacking the entire tetrahydropyran moiety ( 3 ) are described. The syntheses proceeded through the PMB‐ether of an ω‐hydroxy β‐keto aldehyde as a common intermediate which was elaborated into a pair of diastereomeric 1,3‐syn and ‐anti diols by stereoselective Duthaler–Hafner allylations and subsequent 1,3‐syn or anti reduction. One of these isomers was further converted into a tetrahydropyran derivative in a high‐yielding Prins reaction, to provide the precursor for bicyclic analogue 4 . Downstream steps for both syntheses included the substrate‐controlled addition of a vinyl lithium intermediate to an aldehyde, thus connecting the peloruside side chain to C15 (C13) of the macrocyclic core structure in a fully stereoselective fashion. In the case of monocyclic 3 macrocyclization was based on ring‐closing olefin metathesis (RCM), while bicyclic 4 was cyclized through Yamaguchi‐type macrolactonization. The macrolactonization step was surprisingly difficult and was accompanied by extensive cyclic dimer formation. Peloruside A analogues 3 and 4 inhibited the proliferation of human cancer cell lines in vitro with micromolar and sub‐micromolar IC50 values, respectively. The higher potency of 4 highlights the importance of the bicyclic core structure of peloruside A for nM biological activity. 相似文献
17.
d-生物素的不对称全合成研究(Ⅱ) 总被引:2,自引:0,他引:2
1,3-二苄基咪唑啉-2-酮-顺-4,5-二羟酸经脱水、单酯化,折分成分(4S,5R)-顺1,3-二苄基-5-甲氧基羧基-2-氧代咪唑啉-4-羧酸,再经还原环合,硫代成(3aS,6aR)-1,3-二苄基-四氢-4H-噻吩并[3,4-d)咪唑-2,4(1H)-二酮(7),后者经格氏反应、脱水、还原、裂解环合一锅合成(3aR,8aS,8bS)-1,3-二苄基-2-氧代十氢咪唑[3,4-d]噻吩并[1,2-a]锍翁溴化物(11),继而经缩合、开环、水解、脱羧、脱苄而得d-生物素(1),总收率为14.5%。 相似文献
18.
In the presence of catalytic amounts of RhH(PPh3)4 and 1,2-bis(diphenylphosphino)ethane (dppe), 1,3-benzothiazoles, 1,3-benzoxazoles, and benzothiophene reacted with α-(phenylthio)isobutyrophenone giving 2-phenylthio derivatives. Reactive monocyclic heteroaromatics, 1-methyl-1,2,3,4-tetrazole and 2-cyanothiophene were also converted into the 5-phenylthio derivatives. The use of an appropriate phenylthio transfer reagent is crucial for the efficient catalyzed conversion of heteroaromatic C-H bonds into C-S bonds. 相似文献
19.
The reaction of ethylmagnesium bromide, prepared in benzene with one or more molar equivalents of triethylamine, with 2-, 2,4- and 2,4,5-substituted 1,3-dioxolanes has been investigated. Besides β-hydroxyethyl sec-alkyl ethers, the normal products of the ring opening/addition reaction encountered with other Lewis bases, 2-hydroxyethyl enol ethers were formed as products of a ring opening/elimination reaction. Kinetic studies suggest an E1 mechanism for this novel reaction. 相似文献
20.
Yu. B. Koptelov 《Russian Journal of Organic Chemistry》2006,42(10):1510-1515
Treatment of 6-aryl-1,5-diazabicyclo[3.1.0]hexanes with Lewis acids [BF3·Et2O or In(OTf)3] promotes opening of the diaziridine ring, followed by formation of 1,3-dipolar cycloaddition products with N-arylmaleimides. The conversion of the initial diaziridine depends on the nature of the 6-aryl group. Diazabicyclohexanes with donor substituents react quantitatively to give (in the absence of dipolarophiles) the corresponding azomethine imine dimers, 1,2,4,5-tetrazine derivatives. The conversion of diazabicyclohexanes having acceptor substituents is poor; simultaneously, the fraction of the hydrolysis products increases. The stereoselectivity in the 1,3-dipolar cycloaddition, i.e. the ratio of the cis-and trans-adducts, depends on the catalyst and solvent. Azomethine imine dimers react with N-arylmaleimides in the presence of indium(III) trifluoromethanesulfonate to give the same 1,3-dipolar cycloaddition products as those obtained from parent 1,5-diazabicyclohexanes. 相似文献