Highly enantioselective catalytic asymmetric Claisen rearrangement of 2-alkoxycarbonyl-substituted allyl vinyl ethers

Progress in the catalytic asymmetric Claisen rearrangement of 2-alkoxycarbonyl-substituted allyl vinyl ether is reported. Application of a more Lewis acidic catalyst, [Cu{(S,S)-t-Bu-box}](H₂O)₂(SbF₆)₂, afforded β-chiral α-keto ester with an enantiomeric excess up to 99%. We suggest a highly polarized transition state for the Lewis acid-catalyzed Claisen rearrangement in order to explain the experimental results.     

Regioselective boron trichloride-mediated aromatic Claisen rearrangement of resorcinol allyl ethers

The regioselective Claisen rearrangement of resorcinol allyl ethers with boron trichloride was achieved with good selectivity (ca. 13:1) to afford the 6-isomer as major product.     

Metalloporphyrin Cr(TPP)Cl-catalyzed Claisen rearrangement of simple aliphatic allyl vinyl ethers and its unique stereoselectivity

The catalytic Z-selective Claisen rearrangement of simple aliphatic allyl vinyl ethers can be achieved using a chromium(III) porphyrin complex, Cr(TPP)Cl, as a catalyst: Cr(TPP)Cl significantly enhances reversal of E-Z selectivity in the thermal Claisen rearrangement of allyl vinyl ethers, especially, 4,5- and 4,6-disubstituted derivatives, at low catalyst loading.     

A novel variant for the preparation of allyl(propargyl) vinyl ethers and their rearrangement into 5-allyl(allenyl)-5-chloro-2-(2-hydroxyethyloxy)-cyclopent-2-ene-1,4-diones

Reactions of 1,2-di- and 1,2,4-trichloro-6,9-dioxaspiro[4.4]non-1-en-3-ones with sodium 2-propenoxide or sodium 2-propynoxide afforded the corresponding 3-allyloxy or 3-propynyloxycyclopentenones, as well as the products of their subsequent thermal [3,3]-sigmatropic rearrangement. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2067–2068, November, 1997.     

Gold-catalyzed rearrangement of substituted allyl aryl ethers

Triphenylphosphinegold(I) complexes catalyze the Claisen-type rearrangement of aryl allyl ethers to the corresponding branched and linear products. The product distribution depends on the olefin geometry of the allylic ether. Stereochemical transfer experiments support an ionic mechanism.     

Bismuth triflate catalyzed Claisen rearrangement of allyl naphthyl ethers

Bismuth triflate was found to be an efficient catalyst for the Claisen rearrangement of allyl naphthyl ethers. The reaction proceeds smoothly with a catalytic amount of bismuth triflate (20 mol %) to afford the corresponding ortho-allyl naphthol in moderate to good yields in most cases.     

Cascade synthesis of dihydrobenzofuran via Claisen rearrangement of allyl aryl ethers using FeCl3/MCM-41 catalyst

Dihydrobenzofuran as one of the active ingredients of the naturally occurring motif is synthesized by using in situ generation of ortho allyl phenols. Aryl allyl ethers on reacting with catalytic amounts of non noble metal iron (III) chloride supported on MCM-41 under moderate reaction conditions yield dihydrobenzofuran. First step via Claisen rearrangement gives ortho allyl phenol followed by its in situ cyclization to yield dihydrobenzofuran in very good yields. Both Lewis as well as Brønsted acidity of the catalyst as evidenced by Py-FTIR studies was found to catalyze the cascade synthesis of dihydrobenzofuran. The scope of the present strategy was successfully demonstrated for several substrates with varying electronic effects for the synthesis of corresponding dihydrobenzofuran with high yields in a range of 71–86%.     

Iridium(III)-catalyzed tandem Claisen rearrangement-intramolecular hydroaryloxylation of aryl allyl ethers to form dihydrobenzofurans

Iridium(III)-catalyzed tandem Claisen rearrangement and intramolecular hydroaryloxylation of ally aryl ethers is described, which provides a mild method to prepare dihydrobenzofurans.     

Synthesis of cyclic allyl vinyl ethers using Pt(II)-catalyzed isomerization of oxo-alkynes

Several alkynyl epoxides and one alkynyl allyl alcohol were isomerized to cyclic allyl vinyl ethers (3,4-dihydro-2H-1,4-oxazines) using PtCl₂ as the catalyst. Three of these allyl vinyl ethers were converted to 2-hydroxymorpholine derivatives by hydrolysis and two were converted to piperidine derivatives by thermal Claisen rearrangement.     

The synthesis of 2,4-dienyl fluoroalkyl ketones by a tandem three-stage sequence of propargyl 2-fluoroalkylvinyl ether formation, Claisen rearrangement, and allene-to-conjugated diene isomerization

A tandem three stages process to a series of trifluoromethyl and halodifluoromethyl 2,4-unsaturated ketones 4a-c is described. This process started with the preparation of 2-fluoroalkyl substituted propargyl vinyl ether 3a-d by treatment of a mixture of individual ethyl α-per(poly)fluoroalkyl acetates 1a-d and propargyl alcohol 2 in CH₂Cl₂ with the mixed base (Na₂CO₃/TEA) at ambient temperature. When heated in toluene at 80°C, these ethers readily underwent a tandem propargyl-allenyl Claisen rearrangement and isomerization of the resultant 3,4-dienone to give 2,4-unsaturated fluoroalkyl ketones 4a-c (Z/E mixture). The reaction of ethyl α-per(poly)fluoroalkyl acetate 1 with 1-phenyl propargyl alcohol 5 in refluxing CH₂Cl₂ in the presence of the mixed base (Na₂CO₃/TEA) directly afforded the corresponding unsaturated fluoroalkyl ketone 6a-c in one pot. In the presence of NaH, the reaction of ethyl 3-halo-3-fluoroalkylacrylates 8a-b with 1,1-dimethyl propargyl alcohol 9 at −50°C to 0°C also gave the unsaturated fluoroalkyl ketones 10a-b in one pot. The difluorovinyl propargyl ether 11 produced by reduction of 2-bromodifluoromethyl substituted propargyl vinyl ether 3b rearranged in hot benzene to give the corresponding allene 12 bearing a gem-difluoromethylene group in the middle of the aliphatic chain.     

Synthesis of functional polymers bearing cyclic carbonate groups from (2-oxo-1,3-dioxolan-4-yl) methyl vinyl ether

(2-Oxo-1,3-dioxolan-4-yl) methyl vinyl ether (OVE) was synthesized with high yield by addition reaction of glycidyl vinyl ether with carbon dioxide using tetrabutylammonium bromide (TBAB) as a catalyst. OVE was also prepared by reaction with β-butyrolactone or sodium hydrogencarbonate in the presence of TBAB as the catalyst. Poly [(2-oxo-1,3-dioxolan-4-yl) methyl vinyl ether] [P(OVE)] was obtained with high yield by cationic polymerization of OVE catalyzed using boron trifluoride diethyl ether complex in dichloromethane. Polymers bearing pendant 5-membered cyclic carbonate groups were also prepared by radical copolymerization of OVE with some electron-accepting monomers. Furthermore, addition reaction of P(OVE) with alkyl amines yielded the corresponding polymer having pendant 2-hydroxyethyl carbamate residue with high conversions. © 1994 John Wiley & Sons, Inc.     

Synthesis of 4-(thien-2-yl)-substituted coumarins through Lewis acid catalyzed Michael addition of thiophenes to 3-benzoylcoumarins followed by oxidation

3-Benzoyl-4-(thien-2-yl)coumarins have been obtained in good yields according to the S_N^H addition–oxidation protocol, involving the diastereoselective addition of thiophenes at C-4 of 3-benzoylcoumarins under BBr₃ catalysis, followed by oxidation of the intermediate 3,4-trans-3-benzoyl-4-(thien-2-yl)-3,4-dihydrocoumarins with DDQ. This two-step procedure can be regarded as nucleophilic substitution of hydrogen (S_N^H) on the heterocyclic ring of coumarins.     

Copper(II) tetrafluroborate-promoted Meinwald rearrangement reactions of epoxides

Epoxides undergo a highly efficient Meinwald rearrangement in the presence of catalytic quantities of copper(II) tetrafluoroborate to give carbonyl compounds in high yields and with excellent selectivity. The low toxicity and ease of handling of this reagent make it an attractive alternative to the more corrosive or costly Lewis acids frequently employed.     

Direct Ferrier rearrangement on unactivated glycals catalyzed by indium(III) chloride

Anhydrous InCl₃ has been shown to efficiently catalyze the Ferrier rearrangement by a direct allylic substitution of the hydroxyl group at C-3 position of glycals to afford the corresponding 2,3-unsaturated glycosides in high yields at ambient temperature. This methodology obviates the need for protecting and/or activating the C-3 hydroxyl group of glycals. The reaction works in equal ease with both 4,6-di-O-benzyl-d-glucal and 4,6-di-O-benzyl-d-galactal. The mildness of InCl₃ makes this approach compatible for glycosyl acceptors with acid labile groups. The generality of the reaction has been demonstrated with a diversity of alcohols, phenols, and sugar nucleophiles.     

三氟甲基磺酸铜(II)手性衍生物:不对称合成中的一类高效催化剂

三氟甲基磺酸铜 [Cu(OTf) 2 ]与各种手性磷氮配体络合催化不对称合成已取得了巨大进展 .详细评述了近五年来该类手性铜催化剂在各种不对称催化反应中的最新应用     

Short Synthesis of 1-(3-tert-Butyl-1-phenyl-1H-pyrazol-5-yl)-3-(5-(2-morpholinoethoxy)-2H-chromen-8-yl) Urea Derivatives

A short and efficient synthesis of 1-(3-tert-butyl-1-phenyl-1H-pyrazol-5-yl)-3-(5-(2-morpholinoethoxy)-2H-chromen-8-yl) urea derivatives (1a–c), a novel type of p38 MAPK inhibitors, is described. The Claisen thermal rearrangement of arylpropargyl ethers was employd as a key step to synthesize the chromene core. The solvent effect on the ratio of the resultant two isomers of Claisen thermal rearrangement, namely 2-methylbenzofuran and 2H-chromen, was also investigated.     

Studies Culminating in the Total Synthesis and Determination of the Absolute Configuration of (-)-Saudin

A full account of studies that culminated in the total synthesis of both antipodes and the assignment of its absolute configuration of Saudin, a hypoglycemic natural product. Two approaches are described, the first proceeding though bicyclic lactone intermediates and related second monocyclic esters. The former was obtained via asymmetric Diels-Alder cycloaddition and the latter by an asymmetric annulation protocol. Both approaches employ a Lewis acid promoted Claisen rearrangement, with the successful approach taking advantage of bidentate chelation to control the facial selectivity of the key Claisen rearrangement.     

Synthesis of isotactic star-shaped poly(vinyl alcohol)

Isotactic 6-armed star-shaped poly(vinyl alcohol) (PVA) with a narrow molecular weight distribution was successfully prepared by the living cationic polymerization of 6-armed star-shaped poly(tert-butyl vinyl ether) (PTBVE) and subsequent acidic ether cleavage. The PTBVE was synthesized using hexa(chloromethyl) melamine (HCMM) as a hexafunctional initiator and ZnI₂ or ZnCl₂ as an activator in toluene/MC (1/1 v/v) at −70 °C. A better living stability of PTBVE was obtained in the ZnCl₂ activator system. The number average molecular weight and the polydispersity index of the 6-armed star-shaped PTBVE polymerized with ZnCl₂ at −70 °C for 24 h were 156,000 g/mol and 1.47, respectively. The fraction of the mm sequence of the resulting PVA was 52%.     

(E)-N-芳基-3-[2-(8-羟基喹啉基)-乙烯基]咔唑的合成、抗氧化活性及促进鼠骨髓间质干细胞增殖的研究

设计合成了3-[2-(8-羟基喹啉基)-乙烯基]-N-对甲苯基咔唑(8)和3-[2-(8-羟基喹啉基)-乙烯基]-N-对甲氧苯基咔唑(9)两个新的化合物, 用IR, MS, 1H NMR和元素分析确认其结构. 并利用DPPH•方法, 超氧阴离子自由基( )法, 羟基自由基HO•法和噻唑蓝比色法(MTT法)分别测定了目标产物的抗氧化活性和调控鼠骨髓间质干细胞(MSCs)的作用. 结果表明, 这两种化合物对DPPH•自由基、超氧阴离子自由基和羟基自由基具有较强的抗氧化活性, 化合物9在低浓度时对鼠骨髓间质干细胞增殖有很好的促进作用.     

Asymmetric Henry reaction catalyzed by oxazolinyl Cu(II) complexes

A novel family of oxazolinyl copper(II) catalysts have been developed and used as Lewis acid catalysts in the asymmetric Henry reaction of various aldehydes with nitromethane. The corresponding nitroalcohol products were obtained in moderate yields (40–80%) and with moderate enantioselectivity (10–40% ee).