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1.
2-Trimethylsilylmethylenecyclopropane (=3) was synthesized by reaction of lithio methylenecyclopropane with TMSCl. The lithium salt of (=3) reacts with some electrophiles by α- or γ-attack depending on the nature of the electrophile. Whereas alkenylbromides and or alkinylbromide give exclusively α-attack, benzaldehyde reacts with γ-alkylation. 相似文献
2.
Anions , derived from α-methoxyallylphosphine oxides , react with electrophiles in a highly regioselective fashion to give products of α-attack or γ-attack depending upon the substitution pattern of the ylid and the nature of the electrophile. 相似文献
3.
Use of polar solvents in the protocycloaddition of ethenes to anisole greatly increases the regioselectivity of the process and the major adducts reflect 1,2-attack onto the arene. 相似文献
4.
Merle A Battiste Donna.D McRitchie Paul G Gassman William F Reuss Jonathan N Chasman John Haywood-Farmer 《Tetrahedron letters》1979,20(23):2097-2100
Methyl substituent probes at the C-2 and C-2,C-4 positions of -tricyclo[3.2.1.02,4] octan-8-one() have provided kinetic evidence confirming the simultaneity of C-2,C-4 cyclopropane bond cleavage in the rate-determining step for thermal extrusion of carbon monoxide. 相似文献
5.
S.Fazal Hussain M.Tariq Siddiqui G. ManiKumar Maurice Shamma 《Tetrahedron letters》1980,21(8):723-726
Proaporphines undergo light catalyzed rearrangement. Pakistanamine () is thus converted into lumipakistanine (), while pronuciferine () and N-acetylnorpronuciferine () afford the corresponding C-9 hydroxylated aporphines and . Possible biogenetic schemes for the formation of C-8, C-9-, and C-8,9-substituted aporphines are presented. 相似文献
6.
Tekant Gözler Belkis Gözler Amarendra Patra John E. Leet Alan J. Freyer Maurice Shamma 《Tetrahedron》1984,40(7):1145-1150
Konyanin (), obtained from (Rutaceae), is the first known 1,4-dihydroarylnaphthalene lignan in which the lactone carbonyl is bonded to C-3 rather than to C-2. Detailed NMR spectral data have been complied for the accompanying lignans (-)-kusunokinin () and diphyllin (). 相似文献
7.
In the course of our synthetic study of salinomycin (), an ionophorous polyether antibiotic, the γ-lactone () corresponding to the C-21~C-30 fragment (the right fragment) of was synthesized from D-mannitol and ethyl L-lactate as chiral starting materials. The complete stereocontrol for the construction of new chiral centers has been achieved by means of the chelation-controlled Grignard reaction and the tetrahydropyran synthesis via the acid catalyzed epoxide ring opening. 相似文献
8.
Kenji Mori 《Tetrahedron letters》1981,22(35):3431-3432
The absolute configuration at C-3 of A-factor, 2-(6-methylheptanoyl)-3-hydroxymethyl-4-butanolide , was determined to be by synthesizing(3)-(+)-A-factor. 相似文献
9.
Wojciech Dmowski 《Journal of fluorine chemistry》1982,21(2):201-219
1-Phenylpentafluoropropene and its para-substituted analogs are susceptible to nucleophilic attack at both vinylic carbon atoms C-1 and C-2. They react with ethanolio sodium ethoxide to give predominantly substitution products, 1-ethoxy-1-phenyltetrafluoropropenes and 2-ethoxy-1-phenyltetrafluoropropenes , with only little formation of adducts, . 2-ethoxy-1H-1-phenylpentafluoropropanes . Alkenes , where the para-substituent X H,Cl,and CF3 give additionally 1,2-diethoxy-1-phenyltrifluoropropenes and, where X = CF3 also 2,2-diethoxy-1H-1-phenyltetrafluoropropane . Overall regioselectivity of nucleophilic attack of the ethoxide ion on alkenes exhibits the Hammett type correlation with Óp values of substituents X: CH3O and CH3 groups favour the attack on the vinylic carbon C-1, while CF3 and Cl substituents direct the attack on the C-2 carbon of alkenes . The E and Z isomers of 1-ethoxy and 1,2-diethoxy substituted alkenes and were formed in comparable amounts, while the E isomers of 2-ethoxy substituted alkenes were always formed with a 93 – 97 % selectivity. 相似文献
10.
Haru Ogawa Yoshinari Taketugu Taiji Imoto Yōichi Taniguchi Hidefumi Kato 《Tetrahedron letters》1979,20(36):3457-3460
Rearrangement of 2,4-di--pentadienals was described as a consequence of the successive alkyl substitutions on the C-2 and C-4 positions. 1H-FT nmr spectroscopy suggested that the reaction involves ketene as an intermediate. 相似文献
11.
A short, stereoselective synthesis of (±)-warburganal (), its C-9 epimer () and the related sesquiterpene dialdehyde (±)-isotadeonal is presented. 相似文献
12.
On heating the furan endoperoxide () rearranges into the enol ester () and the bicyclic ozonide () affords instead the rearranged ozonide (). The process () → () represents an intramolecular Baeyer-Villiger rearrangement presumably via the dioxirane (D-2), while the process () → () represents intramolecular trapping of the carbonyl oxide (C-3). 相似文献
13.
Sergio Penco Francesco Angelucci Marzia Ballabio Aristide Vigevani Federico Arcamone 《Tetrahedron letters》1980,21(23):2253-2256
Stereoselective epoxidation of , the 7,8-unsaturated derivative of daunomycinone, followed by opening of the epoxide , afforded 8(R)-methoxydaunomycinone ; its configuration at C-8 was determined by chemical correlation and PMR studies. 相似文献
14.
Herbert Muffler Guenter Siegemund Werner Schwertfeger 《Journal of fluorine chemistry》1982,21(2):107-132
4.5-Perfluoro-1.3-dioxolanes are available by reaction of 2(α-chloroalkoxy)perfluoro-carbonyl halides or -ketone with fluoride ions. A mechanism for the intramolecular ring- closure-reaction is proposed. Hydrogen atoms at C-2 in can be exchanged photochemically by chlorine. Starting from the 2-monochloro-derivatives the 2-monofluoro-4.5-perfluoro- 1.3-dioxolanes are formed by reaction with triethylamine- hydrofluoride. 相似文献
15.
Methyl 4-0-benzoyl-6-bromo-6-deoxy-α-D-glucopyranoside (, Figure 1) was converted, via the corresponding ditosylate , into methyl 2,3-di-0-p-toluenesulfonyl-4-0-benzoyl-6-S-acetyl-6-thio-α-D-glucopyranoside () by a selective nucleophilic displacement of 6-bromo-group with thioacetate. Unexpectedly, on treating the compound with an excess of sodium methoxide in benzene-methanol (1:1) at room temperature, methyl 2-0-p-toluenesulfonyl-4,6-thioanhydro-α-D-gulopyranoside () was obtained in a yield of 84%. In order to determine the structure of the relatively unstable oily product , some stable crystalline derivatives (, and ) were prepared. Detailed analysis of the 1H-NMR-spectra (200 MHz) of and gave the conclusive evidence for the structure of A self-imposing mechanism of the clean and smooth transformation of to is proposed, involving: a) formation of (Figure 2) as a crucial intermediate and b) a highly regioselective epoxide opening in (at C-4) by an intramolecular nucleophilic attack of the mercaptide anion from C-6. 相似文献
16.
In pebrolide biosynthesised from MVA-[2.2-3H2], 1, 1 and 2 tritium atoms respectively are retained at C-1, C-15 and C-7. 相似文献
17.
Kenji Mori Hiroko Nomi Tatsuji Chuman Masahiro Kohno Kunio Kato Masao Noguchi 《Tetrahedron letters》1981,22(12):1127-1130
The absolute configuration at C-6 and C-7 of serricornin was established as (6, 7) by synthesizing its (6, 7- and (6, 7- isomers. 相似文献
18.
Hélène Guinaudeau Alan J. Freyer Maurice Shamma Kemal Hüsnü Can Başer 《Tetrahedron》1984,40(11):1975-1982
The new bisbenzylisoquinolines (+)-tha1igrisine and (+)-tha1iphylline () have been isolated from var. . Four rules are described which correlate the structures of Thalictrum bisbenzylisoquinolines with their stereochemistry at C-1 and C-1'. As a result, (+)-tha1rugosamine is shown to be identical with (+)-homoaromo1ine (). (+)-Thalisamine and (+)-N'-norhernandezine are also identical and are represented by expression . The sole exception to the rules is (-)-isothalidezine (). 相似文献
19.
Koichi Hirai Katsumi Fujimoto Yuji Iwano Tetsuo Hiraoka Tadashi Hata Chihiro Tamura 《Tetrahedron letters》1981,22(11):1021-1024
The Δ1-carbapenem derivative() was prepared by the aldol condensation of the dialdehydic compound() with piperidinium acetate. Careful hydride reduction followed by benzoylation gave b, which was successfully decarbalkoxylated to . The X-ray structure analysis of showed the C-3 carboxylate group and C-5 H are each other. 相似文献
20.
Photocyclization of 1,3-bis[2-(2-naphthyl)vinyl]benzene leads regioselectively to dinaphth[1,2-:2′,1′-]anthracene without the need for a blocking bromine substituent at C-2 in the starting material as assumed previously by other workers. 相似文献