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1.
A stereoselective synthesis of coronafacic acid, a natural component of the phytotoxin coronatin, was achieved using an intramolecular Diels-Alder reaction as the key step. The triene precursor bearing a substituted diene and a vinylketone as dienophile was synthesized and then tested in the thermal intramolecular cyclization. We have devised a new strategy to assemble the E,Z-diene through the stereoselective aldol reaction of an ester enolate followed by a stereoselective dehydration. Following the thermal cyclization, the corresponding hydrindanone thereby obtained with the desired relative stereochemistry could easily be converted into the natural product. The synthesis of the coronafacic acid was accomplished in six steps in 29% overall yield. 相似文献
2.
Debendra K. Mohapatra Seetaram Mohapatra Mukund K. Gurjar 《Tetrahedron letters》2006,47(33):5943-5947
Stereoselective intramolecular oxymercuration has been demonstrated as the key reaction for the efficient preparation of mono- and dihydroxylated unsymmetrical bis-tetrahydrofuran skeletons present in naturally occurring biologically active acetogenins using carbohydrates. These trans- and syn-selective intramolecular oxymercurations were explored in an enantioselective synthesis of the bis-tetrahydrofuran skeleton of mucoxin. 相似文献
3.
Kinetic control of the stereoselectivity of protonation of enolates and other delocalized species commonly affords the less stable diastereomer as a consequence of the considerable exothermicity and resulting sp(2) transition-state hybridization of the alpha-carbon. Protonation then is from the less hindered face of the enolate. The present study is aimed at reversing this phenomenon by intramolecular delivery of the proton. The approach employed required the synthesis of two enolate precursors, one with a 2-pyridyl group strategically close to the alpha-carbon and the other with a phenyl group in the same location. The synthesis required 15 steps and involved new methodology. Intramolecular proton transfer, reversing the usual stereoselectivity, was successful. The selectivity proved to depend on several factors including the exo versus endo configuration of the diastereomer reacting, the proton donor employed, and the concentration of the proton donor. A kinetic analysis permitted the determination of the relative reaction orders of the protonation on the two faces of the enolate. 相似文献
4.
S. Z. Vatsadze V. S. Tyurin A. I. Zatsman M. A. Manaenkova V. S. Semashko D. P. Krut’ko N. V. Zyk A. V. Churakov L. G. Kuz’mina 《Russian Journal of Organic Chemistry》2006,42(8):1225-1231
The ring opening in the 1-benzyl-5,7-dimethyl-6-oxo-1-azonia-3-azaadamantane chloride under the treatment with excess aqueous alkali led to a stereoselective formation of anti-1,5-dimethyl-7-benzyl-3-formyl-3,7-diazabicyclo[3.3.1]nonan-9-ol whose structure was established by means of X-ray diffraction analysis and NMR spectroscopy. A reaction mechanism was suggested involving an intramolecular redox hydride transfer. 相似文献
5.
Starting from the Staudinger [2+2] cycloaddition between the 1-azadiene 1 and acetoxyacetylketene, generated in situ from acetoxyacetyl chloride, we developed a seven-step synthesis of the novel azeto[3′,4′:2,3]pyrano[4,5-c]pyrazole skeleton 9 in both racemic and enantiopure forms. Silver carbonate treatment of the functionalised hydrazonoyl chloride 7 promoted in situ generation of the corresponding nitrilimine 8, which underwent a clean, stereoselective cycloaddition to the target tricyclic β-lactam 9. The key step of the synthetic pathway leading to enantiopure 9 was the production of the enantiopure azetidinone (3R,4S)-3 by enzymatic resolution with Amano Lypase PS of the racemic precursor (3S1,4R1)-2. 相似文献
6.
[reaction: see text] Intramolecular cycloadditions with high regio- and stereocontrol are important methods for the efficient assembly of complex molecular structures. Efficient routes to the synthesis of norbornadiene-tethered nitrile oxides have been developed, and their intramolecular 1,3-dipolar cycloadditions were studied. The cycloadditions occurred in good yields for a variety of substrates and were found to be highly regio- and stereoselective. 相似文献
7.
[reaction: see text] A one-pot synthesis of C(2)-symmetric di-d-fructose dianhydrides having the 1,6,9,13-tetraoxadispiro [4.2.4.2]tetradecane skeleton has been accomplished via intramolecular aglycon delivery from (6 --> 6) xylylene-tethered fructofuranose precursors. The stereochemical outcome of the glycosylation-spiroketalization process is governed by the geometrical constraints imposed by the rigid tetracyclic structure of the final compound. 相似文献
8.
The ethylidene acetal of d-erythrose was used as a template for stereoselective IMDA reactions: high endo selectivity and yields in favor of the cis product were observed with 1,3,9-trienes, resulting from a boat transition state. For natural product synthesis, the reaction was successfully applied to a diene with terminal Z-olefin. 相似文献
9.
Efficient intramolecular hydroamination/cyclization of primary and secondary conjugated aminodienes can be effected by using organolanthanide precatalysts of the type Cp'2LnCH(TMS)2 (Cp' = eta5-Me5C5; Ln = La, Sm, Y; TMS = SiMe3) and CGCSmN(TMS)2 (CGC = Me2Si(eta5-Me4C5)(tBuN)). The transformation proceeds cleanly (>/= 90% conversion) at 25-60 degrees C with good rates and high regioselectivities, and with electronic effects leading to significant rate enhancements. Some features of the reaction parallel monosubstituted aminoalkene hydroamination/cyclization, including rate law (zero order in [aminodiene]), and rate enhancements observed with larger lanthanide ionic radii and/or more open catalyst ligation structures. Good to excellent diastereoselectivity is obtained in the synthesis of 2,5-trans-disubstituted pyrrolidines (80% de) and 2,6-cis-disubstituted piperidines (99% de) with using the corresponding alpha-methyl aminodiene precursors. Formation of 2-(prop-1-enyl)piperidine with the chiral C1-symmetric precatalyst (S)-Me2Si(OHF)(CpR*)SmN(TMS)2 (OHF = eta5-octahydrofluorenyl; Cp = eta5-C5H3; R* = (-)-menthyl) proceeds with up to 69% ee. 相似文献
10.
A solid-phase method for the synthesis of tri-, tetra-, and pentacyclic compounds containing tetrahydro-beta-carboline, tetrahydroisoquinoline or analogous scaffolds is presented. The reaction proceeds with high stereoselectivity through an intermediate N-carbamyliminium ion that exclusively converts into Pictet-Spengler-type products with a variety of C-nucleophiles. Amino aldehydes masked with 3-Boc-(1,3)-oxazinane (Box) have been synthesized from amino acids, amino alcohols, or 2-nitro benzaldehydes. The amino moiety of these masked aldehydes has been converted into pentafluorophenyl carbamate to serve as a urea precursor. The building blocks were incorporated at the N-terminal of a resin-supported dipeptide through urea formation. Subsequent treatment with acid liberated the aldehyde quantitatively. A penultimate tryptophan residue gave rise, under the acetic conditions, to a spontaneous intramolecular Pictet-Spengler reaction with the liberated aldehyde. The reaction proceeded with a high degree of stereoselectivity affording tetrahydro-beta-carbolines with a de (de=diastereomeric excess) above 95 % and purity in the range of 90-99 %. This reaction has been extended to a range of other aromatic C-nucleophiles, including substituted indoles, benzenes, pyrene, furan, thiophenes, and benzothiophene with comparable stereoselectivity and purity. Prolonged exposure of the benzaldehyde-derived Pictet-Spengler products to strong acid and air lead to quantitative auto-oxidation which yielded compounds with a 3,4-dihydro-beta-carboline, a 3,4-dihydroisoquinoline, or a similar core structure. 相似文献
11.
A stereoselective intramolecular 1,3-dipolar nitrone cycloaddition useful in the synthesis of chromanes is described. The reaction relies on the use of a chiral auxiliary on the nitrone partner. Key to the success of the reaction is the choice of auxiliary and the choice of Lewis acid catalyst. Utilizing an auxiliary with a pendant coordinating group, and Zn(OTf)(2) as the Lewis acid, diastereoselectivities up to 22:1 could be achieved. 相似文献
12.
Keiichiro Fukumoto Masatoshi Chihiro Yuichi Shiratori Masataka Ihara Tetsuji Kametani Toshio Honda 《Tetrahedron letters》1982,23(29):2973-2976
Thermolysis of a benzocyclobutene derivative () prepared from norcamphor produced stereoselectively a tetracyclic compound (), which was converted to a lactone () having correct stereochemistry at C7, C8, C9, C11, C13, and C14 positions of (±)-klaineanone. 相似文献
13.
[reaction: see text] The type 2 intramolecular N-acylnitroso Diels-Alder reaction has been employed for the synthesis of substituted bridged bicyclic oxazinolactams. Upon oxidation of hydroxamic acid 6, a 3-benzylated oxazinolactam (7) was synthesized with complete diastereoselectivity. Elaboration of cycloadduct 7 liberated a cis-3,7-disubstituted azocin-2-one (9). 相似文献
14.
ortho-Bromocinnamates can be coupled with methyl phenylsulfoximine to afford N-arylsulfoximines in excellent yield. Treatment of these products with an amide base results in a completely stereoselective cyclization to afford enantiomerically pure benzothiazines. This reaction is stereospecific. 相似文献
15.
《Tetrahedron letters》1986,27(8):943-946
Highly diastereoselective intramolecular alkylation of acyclic ester system was developed based upon allylic strain concept as an approach to trans-hydrindane system. 相似文献
16.
Naofumi Naga 《Journal of polymer science. Part A, Polymer chemistry》2006,44(20):6083-6093
The copolymerization of propylene and disubstituted diallylsilanes [(CH2 ?CH? CH2? )2R2Si (R = CH3 or C6H5)] was investigated with isoselective and syndioselective zirconocene catalysts with methylaluminoxane as a cocatalyst. The syndioselective catalyst showed a higher reactivity for disubstituted diallylsilanes than the isoselective catalysts. Diallyldimethylsilane was incorporated into the polymer chain via cyclization insertion preferentially and formed 3,5‐disubstituted dimethylsilacyclohexane units in the polypropylene main chain. In the copolymerization with diallyldiphenylsilane, diallyldiphenylsilane was copolymerized via both cyclization insertion and 1,2‐insertion, which formed a pendant allyl group. The structures of isolated silacyclohexane units, determined by 13C NMR and distortionless enhancement by polarization transfer spectroscopy, proved that the 1,2‐insertion of diallylsilanes proceeded with enantiomorphic site control; however, the diastereoselectivity of the cyclization reaction was independent of the stereoselectivity of the catalysts used, and cis‐silacyclohexane units were mainly formed. © 2006 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 44: 6083–6093, 2006 相似文献
17.
G. Srinivas Rao Neela Sudhakar B. Venkateswara Rao S. Jeelani Basha 《Tetrahedron: Asymmetry》2010,21(16):1963-1970
The formal synthesis of 3-epi jaspine B was achieved by using a stereoselective intramolecular oxa-Michael addition. The diacetate derivative of 3-epi jaspine B was also synthesized. 相似文献
18.
Satwinder Singh 《Tetrahedron letters》2007,48(47):8270-8273
The first asymmetric synthesis of (+)-iso-6-cassine is described. Lipase-catalyzed resolution, enantioselective Overman rearrangement, and diastereoselective intramolecular amidomercuration were used for the installation of the three stereocenters in (+)-iso-6-cassine, and cross-metathesis was employed for the attachment of the side-chain. 相似文献
19.
Ko C Hsung RP Al-Rashid ZF Feltenberger JB Lu T Yang JH Wei Y Zificsak CA 《Organic letters》2007,9(22):4459-4462
A stereoselective halo-etherification of chiral enamides is described here. This work provides an approach to halogen containing cyclic ethers and reveals further mechanistic insights to the chemistry of chiral enamides. 相似文献