- Reactivity of cyclopropanic δ-oxo-α,β-unsaturated esters towards SmI2: 3-exo-trig cyclisation versus cyclopropane ring opening
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trans-(2′,2′-Diphenyl-bicyclopropyl-2-yl)-4,4-dimethyl-5-oxo-pent-2-enoic acid methyl ester 9, undergoes 3-exo-trig cyclisation in the presence of SmI2 without competitive ring opening of Newcomb's bicyclopropylic probe next to the carbonyl gro
- Cammoun, Chama,Zriba, Riadh,Bezzenine-Lafollée, Sophie,Guibé, Fran?ois
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Read Online
- Direct and Stereospecific [3+2] Synthesis of Pyrrolidines from Simple Unactivated Alkenes
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Pyrrolidines are important heterocyclic compounds with endless applications in organic synthesis, metal catalysis, and organocatalysis. Their potential as ligands for first-row transition-metal catalysts inspired a new method to access complex poly-heterocyclic pyrrolidines in one step from available materials. This fundamental step forward is based on the discovery of an essential organoaluminum promoter that engages unactivated and electron-rich olefins in intermolecular [3+2] cycloadditions.
- Otero-Fraga, Jorge,Suárez-Pantiga, Samuel,Montesinos-Magraner, Marc,Rhein, Dennis,Mendoza, Abraham
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supporting information
p. 12962 - 12966
(2017/09/18)
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- Evidence that Additions of Grignard Reagents to Aliphatic Aldehydes Do Not Involve Single-Electron-Transfer Processes
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Addition of allylmagnesium reagents to an aliphatic aldehyde bearing a radical clock gave only addition products and no evidence of ring-opened products that would suggest single-electron-transfer reactions. The analogous Barbier reaction also did not pro
- Otte, Douglas A. L.,Woerpel
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p. 3906 - 3909
(2015/08/18)
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- Diazo- And transition-metal-free C-H insertion: A direct synthesis of β-lactams
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Carbene intermediates are very useful species for a range of reactions including C-H insertions and cycloadditions. They are most commonly generated by metal-catalyzed release of nitrogen gas from diazo precursors. Herein, we present a novel C-H insertion
- Gomes, Luis F. R.,Veiros, Ls F.,Maulide, Nuno,Afonso, Carlos A. M.
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p. 1449 - 1453
(2015/01/30)
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- Aryl-substituted cyclopropyl acetylenes as sensitive mechanistic probes in the gold-catalyzed hydration of alkynes. comparison to the Ag(I)-, Hg(II)-, and Fe(III)-catalyzed processes
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The gold-catalyzed hydration of 2-phenyl- or 2,2-diphenylcyclopropyl acetylene, sensitive probes to trace the formation of vinyl carbocations, provides exclusively the corresponding cyclopropyl methyl ketones. On the other hand, in the Ag(I)- or Fe(III)-c
- Velegraki, Georgia,Stratakis, Manolis
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p. 8880 - 8884
(2013/09/24)
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- Cyclopropanes in Nicholas reaction: Formation of spiroketals with a five-membered and a seven- or an eight-membered ring This paper is dedicated to Professor Paul A. Wender, one of the most creative contributors to the broad discipline of organic chemistry, on the occasion of the Tetrahedron Prize
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The consecutive treatment of 5-hydroxy-1-pentynyl 2,2-disubstituted- cyclopropyl ketones with Co2(CO)8 and BF 3·OEt2 produced the corresponding Co 2(CO)6-complexed dioxaspiro[4.6] derivatives. The one-carbon homologated substrates also afforded dioxaspiro[4.7]. It was found that this procedure can be applied to the substrates with gem-disubstituents as well as a mono-aryl substituent on the cyclopropane, but the mono-alkyl substituted cyclopropanes are insufficient.
- Mukai, Chisato,Kojima, Takahiro,Kawamura, Takamasa,Inagaki, Fuyuhiko
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p. 7659 - 7669
(2013/08/23)
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- 1-[(E)-2-arylethenyl]-2,2-diphenylcyclopropanes: Kinetics and mechanism of rearrangement to cyclopentenes
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Kinetic measurements for the thermal rearrangement of 2,2-diphenyl-1-[(E)- styryl]cyclopropane (22a) to 3,4,4-triphenylcyclopent-1-ene (23a) in decalin furnished ΔHρm{{-{isom}^{ne }}}$=31.0±1.2kcal mol-1 and ΔSρm{{-{isom}^{ne }}}$=-6. 0±2.6e.u. The lowering of ΔHa‰ by 20kcal mol-1, compared with the rearrangement of the vinylcyclopropane parent, is ascribed to the stabilization of a transition structure (TS) with allylic diradical character. The racemization of (+)-(S)-22a proceeds with ΔHρm{{-{rac}^{ne }}}$=28.2±0.8kcal mol -1 and ΔSρm{{-{rac}^{ne }}}$=-5±2e.u., and is at 150° 106 times faster than the rearrangement. Seven further 1-(2-arylethenyl)-2,2-diphenylcyclopropanes 22, (E)- and (Z)-isomers, were synthesized and characterized. The (E)-compounds showed only modest substituent influence in their krac (at 119.4°) and kisom (at 159.3°) values. The lack of solvent dependence of rate opposes charge separation in the TS, but a linear relation of log krac with log p.r.f., i.e., partial rate factors of radical phenylations of ArH, agrees with a diradical TS. The ring-opening of the preponderant s-trans-conformation of 22 gives rise to the 1-exo-phenylallyl radical 26 that bears the diphenylethyl radical in 3-exo-position, and is responsible for racemization. The 1-exo-3-endo-substituted allylic diradical 27 arises from the minor s-gauche-conformation of 22 and is capable of closing the three- or the five-membered ring, 22 or 23, respectively. The discussion centers on the question whether the allylic diradical is an intermediate or merely a TS. Quantum-chemical calculations by Houk etal. (1997) for the parent vinylcyclopropane reveal the lack of an intermediate. Can the conjugation of the allylic diradical with three Ph groups carve the well of an intermediate? Copyright
- Mulzer, Johann,Huisgen, Rolf,Arion, Vladimir,Sustmann, Reiner
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p. 1359 - 1388
(2011/10/09)
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- SmI2-mediated reductive cross-coupling reactions of -cyclopropyl nitrones
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Three new α-cyclopropyl nitrones have been synthesized as mechanistic probes for reductive cross-coupling reactions of nitrones. The α-cyclopropylcarbinyl radical intermediate formed by single electron transfer from SmI2 to these nitrones is no
- Burchak, Olga N.,Masson, Geraldine,Py, Sandrine
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scheme or table
p. 1623 - 1626
(2010/09/05)
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- Concerning the reactivity of ptad with isomeric dienes: The mechanism of the Diels-Alder cycloaddition
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Cyclopropyl substituted dienes are employed as mechanistic probes in the triazolinedione Diels-Alder (DA) reaction. In aprotic and protic solvents, apart from the DA adducts that bear an intact cyclopropyl group, complicated and rearranged products are also obtained. These results provide solid evidence for the involvement of an open intermediate with a lifetime greater than 2 x 10 -12 s.
- Alberti, Mariza N.,Orfanopoulos, Michael
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supporting information; experimental part
p. 1659 - 1662
(2009/09/07)
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- Facile and efficient way to synthesize the radical cyclization precursor methyl 3-(tert-butyl((E)-3-(2,2-diphenylcyclopropyl)-2-propenyl)amino)-3-oxo-2- (phenylseleno)propanoate for kinetic research
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Methyl 3-(tert-butyl((E)-3-(2,2-diphenylcyclopropyl)-2-propenyl)amino)-3- oxo-2-(phenylseleno)propanoate was prepared in 10 steps in good to excellent yield using benzophenone and hydrazine hydrate as the starting materials. Copyright Taylor & Francis Group, LLC.
- Yu, Jindi,Lian, Gaoyan,Zhang, Danwei
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- Thermal C2-C6 cyclization of enyne-allenes. Experimental evidence for a stepwise mechanism and for an unusual thermal silyl shift
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Enyne-allenes 4a-c bearing various cyclopropyl systems as radical clock reporter groups at the allene terminus have been synthesized and subjected to thermal C2-C6 cyclization. The ratio of ene versus formal Diels-Alder products could be rationalized on the basis of steric effects. Only the thermolysis of 4c, equipped with the fast diphenylcyclopropylcarbinyl radical clock, afforded a 1,3-butadienyl benzofulvene clearly formed via cyclopropyl ring opening. This finding provides unambiguous evidence for a stepwise mechanism of the C2-C6 cyclization making it possible to suggest a lifetime for the intermediate diradical of > 1 × 10-10 s (at 170 °C). An interesting corollary was the isolation of an unexpected silyl shift product in the thermolysis of all three enyne-allenes that allows explanation of the loss of the TIPS group in some of the Diels-Alder products. For a full understanding of the mechanism, silyl and hydrogen shift processes were interrogated using DFT.
- Schmittel, Michael,Mahajan, Atul A.,Bucher, Goetz,Bats, Jan W.
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p. 2166 - 2173
(2007/10/03)
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- Stereocontrol of intramolecular Diels-Alder reactions by an allylic diphenylcyclopropyl group
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Intramolecular Diels-Alder reactions of ester-linked 1,3,8-nonatrienes carrying a diphenylcyclopropyl substituent attached to C1 proceed with high levels of stereoselectivity. The stereochemical outcomes of these reactions are explained by reference to B3
- Tripoli, Regis,Cayzer, Tory N.,Willis, Anthony C.,Sherburn, Michael S.,Paddon-Row, Michael N.
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p. 2606 - 2616
(2008/03/12)
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- p-Nitrobenzenesulfenate esters as precursors for laser flash photolysis studies of alkyl radicals
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A series of p-nitrobenzenesulfenate esters was used in laser flash photolysis (LFP) studies to generate alkoxyl radicals that fragmented to give the (2,2-diphenylcyclopropyl)methyl radical. Rate constants for the β-scission reactions increased as a function of the carbonyl compound produced in the fragmentation reaction in the order CH2O 2CO 2CO and increased with increasing solvent polarity. For alkoxyl radicals that fragment to produce benzaldehyde and benzophenone, the β-scission reactions are faster than 1,5-hydrogen atom abstractions when the incipient carbon radical is as stable as a secondary alkyl radical, and this entry to carbon radicals can be used in LFP kinetic studies.
- Newcomb, Martin,Daublain, Pierre,Horner, John H.
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p. 8669 - 8671
(2007/10/03)
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- Cyclopropylpropenamides
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The invention relates to compounds of the formula STR1 Y is O or S, *A is paraphenylene or *--(CH2)n --(X)m --(CH2)r --, X is O, S or --CH=CH--, n or r, independently, are integers from 0 to 3, s is an integer from 0 to 1, m is an integer from 0 to 1, provided that when m is 1, n+s must be at least 2, R1 and R2, independently, are hydrogen, lower alkyl, cycloalkyl, lower alkenyl, Het or aryl, *E is STR2 or --(CH2)k -- wherein k is an integer from 0 to 4, R3, R4 and R8 are independently hydrogen or lower alkyl, R5 and R6, independently are hydrogen or lower alkyl, R7 is hydrogen, lower alkyl, cycloalkyl, Het-lower alkyl or aryl, Het is a monocyclic 5- or 6-membered hetero aromatic or a bicyclic heteroaromatic radical containing one or two hetero atoms selected from nitrogen, oxygen and sulfur, which radical may be substituted by lower alkyl, halogen or aryl, and the asterisk denotes the point of attachment, and their enantiomers, diastereomers and racemic mixtures thereof, as well as when *E is STR3 their geometric isomers, and pharmaceutically acceptable acid addition salts thereof. The compounds of formula I exhibit activity as platelet activating factor (PAF) antagonists and are, therefore, useful in disease states characterized by excess platelet activating factor or for the prevention and treatment of cardiovascular diseases, pulmonary diseases, immunological disorders, inflammatory diseases, dermatological disorders, shock or transplant rejection.
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