- 1-HALOCYCLOPROPENES AND PROPARGYLIC HALIDES FROM THE REACTION OF TRIHALOCYCLOPROPANES WITH METHYL LITHIUM
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1,1,2-Trihalocyclopropanes (halogen=chlorine or bromine) undergo 1,2-dehalogenation on reaction with methyl lithium, and in a number of cases the product is a 1-halocyclopropene.In the reactions of (20, X=Br, Cl) and (25) a rearrangement occurs even at low temperatures and propargylic halides are isolated, while (16) is converted to 2-chlorocyclohex-2-enylidene which may be trapped by furan.
- Baird, Mark S.,Nethercott, William
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- Total synthesis of (+)-frondosin A. Application of the RU-catalyzed [5+2] cycloaddition
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The first total synthesis of (+)-frondosin A was accomplished in 19 longest linear and 21 total steps from commercially available materials. The key features of the synthesis include a Ru-catalyzed [5+2] cycloaddition, a Claisen rearrangement, and a ring expansion to construct the core of the frondosin A in a diastereoselective and regioselective fashion. This is the first application of a Ru-catalyzed [5+2] cycloaddition in the total synthesis of a natural product. Through this synthesis, the absolute configuration of (+)-frondosin A was established.
- Trost, Barry M.,Hu, Yimin,Horne, Daniel B.
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- Double-diels-alder approach to maoecrystal V. unexpected C-C bond-forming fragmentations of the [2.2.2]-bicyclic core
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Synthetic studies toward maoecrystal V are reported. An oxidative dearomatization/Diels-Alder cascade to assemble the natural product carbocyclic core in one step is proposed. A facile electrocyclization is shown to suppress the intramolecular allene Diel
- Smith, Brandon R.,Njardarson, Jon T.
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supporting information
p. 5316 - 5319
(2017/11/07)
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- Silver-Catalyzed Three-Component 1,1-Aminoacylation of Homopropargylamines: α-Additions for Both Terminal Alkynes and Isocyanides
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The reaction of secondary homopropargylamines, isocyanides, and water in the presence of a catalytic amount of silver acetate and subsequent purification by chromatography on silica gel afforded substituted proline amides in good to excellent yields. Primary homopropargylamines underwent a cyclizative Ugi–Joullié three-component reaction with isocyanides and carboxylic acids to afford functionalized N-acyl proline amides. High diastereoselectivity was observed in the synthesis of 4-alkoxy and 4,5-disubstituted proline derivatives. This work represents the first examples of a three-component cyclizative 1,1-aminoacylation of terminal alkynes.
- Tong, Shuo,Piemontesi, Cyril,Wang, Qian,Wang, Mei-Xiang,Zhu, Jieping
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supporting information
p. 7958 - 7962
(2017/06/27)
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- Ruthenium-Catalyzed Hydroalkynylative Cyclization of 1,6-Enynes Induced by Substituent Effects
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The ruthenium-catalyzed 1,6-enyne cyclization in the presence of bulky substituted terminal alkyne proceeds smoothly at room temperature to afford highly substituted five-membered cyclic compounds featuring a 1,5-enyne motif. Deuterium-labeling experiment
- Liu, Rui,Ni, Zhenjie,Giordano, Laurent,Tenaglia, Alphonse
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supporting information
p. 4040 - 4043
(2016/08/30)
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- Total synthesis of bryostatins: The development of methodology for the atom-economic and stereoselective synthesis of the ring C subunit
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Bryostatins, a family of structurally complicated macrolides, exhibit an exceptional range of biological activities. The limited availability and structural complexity of these molecules makes development of an efficient total synthesis particularly impor
- Trost, Barry M.,Frontier, Alison J.,Thiel, Oliver R.,Yang, Hanbiao,Dong, Guangbin
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scheme or table
p. 9762 - 9776
(2011/10/05)
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- Palladium(0) catalyzed regioselective carbonyl propargylation across tetragonal tin(II) oxide via redox transmetallation
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Facile homopropargylation of aldehydes by propargyl bromides over tetragonal tin(II)oxide and catalytic palladium(0) occurs which is proposed to involve the prior formation of dinuclear allenylpalladium followed by redox transmetallation to β-SnO.
- Banerjee, Moloy,Roy, Sujit
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p. 534 - 535
(2007/10/03)
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- A McMurry route to the dienediyne portion of models of the neocarzinostatin chromophore
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The 6-ring/10-ring dienediyne model 11 of the antitumor agent neocarzinostatin chromophore 1 and its 6-ring/11-ring homolog 12 have been obtained in 41 and 18% yields, respectively, by McMurry cyclizations of ketoaldehydes 8 and 9 using TiCl3·2DME and Zn/Cu couple. Compounds 8 and 9 were obtained by rnultistep syntheses starting from the readily available acetylenic aldehydes HC=CC(CH3)2-(CH2)nCH=O (18, n = 1, 21, n = 2). Dienediyne 11 was converted into the dienediyne ketone 33 which cycloaromatized at room temperature giving the octahydrophenanthrone 35 in 16% yield.
- Rank, Elisabeth,Brueckner, Reinhard
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p. 1045 - 1053
(2007/10/03)
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- The Preparation and Lithiation of 1-Halogenocyclopropenes
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Reaction of a range of 1,1,2-trihalogenocyclopropanes (halogen = bromine, chlorine) with methyl-lithium in ether at -90 - 20 deg C leads to 1,2-dehalogenation to the corresponding 1-halogenocyclopropene.The halogenocyclopropenes are readily lithiated by lithium-halogen exchange with a second equivalent of methyl-lithium to give 1-lithiocyclopropenes, which are in turn trapped by electrophiles; an exception to this is compound (21; X = Cl), which leads to 3-methylbuta-1,2-dienylidene (31) by initial lithium-hydrogen exchange and loss of lithium chloride.The cyclopropenes (5; R = Me, X = Br or Cl) and (21; X = Br or Cl) decompose even at temperatures around ambient, leading either to enynes (6; R = Me) or halogenoalkynes (18; X = Br or Cl).A 12C-labelling study indicates that C-1 of the cyclopropene (21; X = Cl) becomes C-2 of the alkyne (18; X = Cl) on rearrangement.
- Baird, Mark S.,Hussain, Helmi H.,Nethercott, William
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p. 1845 - 1854
(2007/10/02)
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- Cycloaddition Reactions of Allenyl Cations with Cyclopentadiene
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Propargyl halides R1-C=-C-CR2R3X (14) and cyclopentadiene react with zinc halide catalysis in ether/dichloromethane solution to give 3-halogenobicycloocta-2,6-dienes 13 (R1 = alkyl) or 5-(α-halogenobenzylidene)norbornenes 15 (R1 = aryl).The reactions are interpreted by stepwise - and -cycloadditions of intermediate allenyl cations 1, proceeding via propargylcyclopentenyl cations 5 and bicyclic vinyl cations 9 or 12.If the reactions are initiated by equimolar amounts of silver trifluoroacetate, quenching products of all postulated intermediates are isolated.The relative energies of the intermediate carbenium ions are estimated on the basis of force field calculations and of gas phase stabilities of simple carbocations.Stereochemical studies indicate that the addition reactions proceed via the compact transition state 42 rather than 41.The zinc chloride catalysed reaction of propargyl chloride 14e with cyclopentadiene yields the 2:1 product 17 (structurally assigned by X ray analysis) in addition to the 1:1 product 15e.The formation of 17 is rationalised by a -cycloaddition of allenyl cation 1 with cyclopentadiene.
- Mayr, Herbert,Halberstadt-Kausch, Inge K.
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p. 3479 - 3515
(2007/10/02)
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