- Application of Rh-catalyzed cyclization for the construction of three consecutive chiral carbons in 4,9-dimethylspiro[4.4]nonane-2,7-dione
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Asymmetric cyclization using Rh-complexes has been applied to the synthesis of 4,9-dimethylspiro[4.4]nonane-2,7-diones. The spiro[4.4]nonane skeleton bearing three consecutive chiral carbons could be stepwisely constructed from an identical starting material by the combination of a cationic Rh[(S)-BINAP]ClO4 and a neutral RhCl(PPh3)3. The relationship between the stereochemistry of the spirodiketones and the Rh-complex was also discussed. (C) 2000 Elsevier Science Ltd.
- Takahashi,Tanaka,Sakamoto,Imai,Matsui,Funakoshi,Sakai,Suemune
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- Enatio- and diastereoselective construction of 4,9-dimethylspiro[4.4]nonane-2,7-dione using Rh-catalyzed asymmetric cyclization
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Asymmetric cyclization using Rh-complexes was applied to the synthesis of 4,9-dimethylspiro[4.4]nonane-2,7-diones. The spiro[4.4]nonane skeleton bearing a chiral quaternary carbon could be stepwisely constructed by using Rh-catalyzed cyclization twice. All diastereomers of the spirodiketone could be stereoselectively prepared from the identical starting material by the combination of a neutral Rh(PPh3)3Cl and a cationic Rh[BINAP]ClO4. The cyclization by the neutral Rh(PPh3)3Cl proceeded to give cis-3,4-disubstituted cyclopentanones, while that by the cationic Rh[BINAP]ClO4 proceeded to afford trans-3,4-disubstituted cyclopentanones. Four spirodiketones of six stereoisomers could be prepared in optically active form, and the relationship between the stereochemistry of the spirodiketones and the Rh-complex was discussed based on the plausible acyl-hydride Rh-complexes.
- Tanaka, Masakazu,Takahashi, Miyuki,Sakamoto, Eishi,Imai, Masanori,Matsui, Akiko,Fujio, Masakazu,Funakoshi, Kazuhisa,Sakai, Kiyoshi,Suemune, Hiroshi
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- Application of Rh-catalyzed cyclization to the formation of a chiral quaternary carbon
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Rh-Catalyzed cyclization was applied to the formation of a chiral quaternary carbon. It has become clear that the Rh-complex can discriminate between isopropenyl and 2-isopentenyl (or isopentyl) substituents, and the cyclization afforded 3,3,4-trisubstituted cyclopentanones with a chiral quaternary carbon in a stereoselective manner. The cyclization of 4-pentenals 6a, b by an achiral neutral Rh(PPh3)3Cl afforded 3,3,4-cis-trisubstituted cyclopentanones (±)-7a, b in 86-96%, and the cyclization by a cationic Rh[(R)-BINAP]ClO4 afforded 3,3,4-trans-trisubstituted cyelopentanones (-)-8a, b of 82-86% ee in 88-98% yields. The mechanism of stereoselection by Rh-complexes is also discussed.
- Takahashi,Tanaka,Sakamoto,Imai,Funakoshi,Sakai,Suemune
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- Synthesis and Characterisation of the C30-De-ethylaetioporphyrin Present in Petroleum
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The four de-ethyl analogues of the relatively ubiquitous and biogenetically significant petroporphyrin aetioporphyrin III (3a-d) have been synthesized utilising the ac-biladiene route.A reversed-phase HPLC method of separating a mixture of the four synthe
- Clewlow, Paul J.,Jackson, Anthony H.
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p. 1925 - 1936
(2007/10/02)
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- Synthetic and Biosynthetic Studies of Porphyrins. Part 8. Synthese of Hepta-, Hexa-, and penta-carboxylic Porphyrins Related to Urophorphin-I
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The title porphyrins of interest as abnormal metabolits in porphyrins biosynthesis, have been synthesized by the Fischer, and b-oxobilane routes, and compared with the naturally derived materials.Enzymic experiments have shown that the conversion of uropo
- Jackson, Anthony H.,Supphayen, Damrus
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p. 277 - 286
(2007/10/02)
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- Pyrrole Chemistry. An Improved Synthesis of Ethyl Pyrrole-2-carboxylate Esters from Diethyl Aminomalonate
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Ethyl pyrrole-2-carboxylates, versatile precursors for the total synthesis of both synthetic model and naturally occurring tetrapyrroles and porphyrins, can be prepared in greatly improved yields by the addition of 1,3-diketones and preformed diethyl aminomalonate to boiling glacial acetic acid.The method is suitable for both small- and large-scale synthesis and has proved far more reliable than the original in situ dissolving zinc reduction of diethyl oximinomalonate discovered by Kleinspehn.Yields range from 60-70percent for the dominant product isomer from unsymmetrical diketones to 75-90percent for the single product derived from symmetrical diketones.Seventeen examples of alkyl-substituted ethyl pyrrole-2-carboxylates are provided.Improved procedures are given for the preparation of the required precursors.
- Paine, John B.,Dolphin, David
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p. 5598 - 5604
(2007/10/02)
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- Pyrazol-4-acetic acid compounds
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Pyrazol-4-acetic acid compounds, such as substituted pyrazol-4-acetic acid, its esters, amides, nitriles and their pharamaceutically acceptable salts and method for the preparation of these compounds are disclosed. The novel compounds are useful analgesics, anti-inflammatory, and antipyretics.
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