Cu(I)-Catalyzed Regioselective Synthesis of Polysubstituted Furans from Propargylic Esters via Postulated (2-Furyl)carbene Complexes

Barluenga, José; Riesgo, Lorena; Vicente, Rubén; López, Luís A.; Tomás, Miguel

doi:10.1021/ja8058342

Cited by 116 publications

(36 citation statements)

References 23 publications

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“…The initial isomerization of the propargylic substrate 6 to the (E)-Knoevenagel intermediate IV then undergoes a 5-exo-dig cyclization to generate the putative 2-furyl copper(I) carbene species V, as already reported. [9] Now, the carbenoid nature of V is strongly supported as it cyclopropanates substrate 1 leading to the cyclopropyldiazo intermediate VI, which in turn undergoes the metal-catalyzed ring expansion to the final cyclobutene 7. As in the case of the PMP-substituted diazo substrates 2 (Table 1 and Scheme 1), the furyl substituent in VI perfectly controls the regioselectivity affording a single cyclobutene.…”

Section: Methodsmentioning

confidence: 99%

Discrimination of Diazo Compounds Toward Carbenoids: Copper(I)‐Catalyzed Synthesis of Substituted Cyclobutenes

et al. 2009

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In the last few years the role of diazo compounds in organic synthesis, particularly in cyclization reactions via metal carbenoids (metal: ruthenium, copper, rhodium, etc.) has been prominent. [1] By taking advantage of the ease with which these metal carbenes collapse into the corresponding symmetrical alkenes (homocoupling), we and others have been able to access nonsymmetrical alkenes by the selective heterocoupling of diazoacetate esters with copper(I) [2] and ruthenium(II) [3] carbene complexes [Eq. (1)]. Interestingly, the metal-catalyzed selective cross-coupling reaction between two different diazo substrates has been reported recently [Eq. (2)]. [4] At this point, we became intrigued as to whether discrimination between appropriately selected diazo compounds, for instance simple diazo and vinyldiazo systems, could be attained. Firstly, we found that [Cu(MeCN) 4 ]BF 4 catalyzes the reaction between ethyl vinyldiazoacetate and ethyl diazoacetate at room temperature. Surprisingly, the expected cross-coupling conjugated diene was not formed, but diethyl 2-methylcyclobutene-1,3-dicarboxylate was obtained in moderate yield as the sole heterocoupling product [Eq. (3)].This initial result seems to encompass, among others, two relevant features: 1) it represents a novel [3+1] coupling between diazo compounds, wherein two CÀC bonds rather than one C=C bond are formed, and 2) it might provide direct access to a relevant, uncommon structure. Therefore, herein we report our preliminary studies on the synthesis of cyclobutene structures by copper(I)-catalyzed cyclization of vinyldiazoacetate esters and diazo compounds (Table 1).First, [Cu(MeCN) 4 ]BF 4 (5 mol %) was added to a solution of ethyl 2-diazo-3-methylbut-3-enoate 1 a (R 1 = Me) and ethyl diazoacetate 2 a (R 2 = CO 2 Et, R 3 = H) in CH 2 Cl 2 at room temperature. After stirring the reaction mixture for two hours the solvent was removed and the resulting mixture was subjected to column chromatography, affording the cyclobutene 3 aa in 33 % yield along with ethyl maleate and ethyl fumarate (entry 1). The yield could be increased to 45 % using tert-butyl diazoacetate 2 b (entry 2). The cyclization of 1 a with

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Section: Methodsmentioning

confidence: 99%

Discrimination of Diazo Compounds Toward Carbenoids: Copper(I)‐Catalyzed Synthesis of Substituted Cyclobutenes

et al. 2009

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“…237 The reaction was presumed to proceed through formation of a copper carbene intermediate following cyclization. When the reaction was carried out under air, moderate yields of the oxidized 2-acylfuran products were formed (Scheme 83).…”

Section: Reactions Of Hydrocarbonsmentioning

confidence: 99%

Aerobic Copper-Catalyzed Organic Reactions

et al. 2013

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24 peroxide [Cu I (pyr)(tpb)] 10 mol % TBHP, 1 atm O 2 , 1:2 AcOH/pyr, rt, 24 h ∼2.5 26 74 g 35 25 n-hexane aldehyde CuCl 2 , 18-crown-6 1 atm O 2 , MeCHO, CH 2 Cl 2 , 70 °C, 24 h 2.4 91 h 9 34a 26 n-decane aldehyde Cu II Cl 16 Pc-AM(PS) 3 equiv of PhCHO, MeCN, 1 atm O 2 , 50 °C 15.4 100 i 61 a See Chart 2 for ligand structures. b Also 28% cyclohexene. c Also 26% cyclohexene. d Mixture of alcohol and hydroperoxide. e Remainder of product is cyclohexene. f Approximately 93:7 of 1-adamantol/2-adamantol. g Approximately 98:2 of 1-adamantol/2-adamantol. h Afforded oxidation products in an approximately 1:1 ratio at the 2-and 3-positions. i Mixture of decanones.

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“…91 The reaction required Barluenga and co-workers have shown that bis-propargylic esters rearrange to enynones upon addition of Cu(I) catalysts, which subsequently cycloisomerize to copper(I) 2-furylcarbene complexes (Scheme 38). 92 These complexes react with silanes and germanes to generate furans in very good yields. The copper carbene intermediates can also be oxidized by air to generate ketones or reacted with ethyl diazoacetate to form alkenes.…”

Section: Scheme 36mentioning

confidence: 99%