- Intramolecular [2+2] Photocycloaddition of Cyclic Enones: Selectivity Control by Lewis Acids and Mechanistic Implications
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The intramolecular [2+2] photocycloaddition of 3-alkenyl-2-cycloalkenones was performed in an enantioselective fashion (nine representative examples, 54–86 % yield, 76–96 % ee) upon irradiation at λ=366 nm in the presence of an AlBr3-activated oxazaborolidine as the Lewis acid. An extensive screening of proline-derived oxazaborolidines showed that the enantioface differentiation depends strongly on the nature of the aryl group at the 3-position of the heterocycle. DFT calculations of the Lewis acid–substrate complex indicate that attractive dispersion forces may be responsible for a change of the binding mode. The catalytic [2+2] photocycloaddition was shown to proceed on the triplet hypersurface with a quantum yield of 0.05. The positive effect of Lewis acids on the outcome of a given intramolecular [2+2] photocycloaddition was illustrated by optimizing the key step in a concise total synthesis of the sesquiterpene (±)-italicene.
- Poplata, Saner,Bauer, Andreas,Storch, Golo,Bach, Thorsten
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supporting information
p. 8135 - 8148
(2019/05/29)
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- Evidence for Triplet Sensitization in the Visible-Light-Induced [2+2] Photocycloaddition of Eniminium Ions
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Εniminium ions were prepared from the corresponding α,β-unsaturated carbonyl compounds (enones and enals), and were found to be promoted to their respective triplet states by energy transfer. The photoexcited intermediates underwent intra- or intermolecular [2+2] photocycloaddition in good yields (50–78 %) upon irradiation at λ=433 nm or λ=457 nm. Iridium or ruthenium complexes with a sufficiently high triplet energy were identified as efficient catalysts (2.5 mol % catalyst loading) for the reaction. The intermolecular [2+2] photocycloaddition of an eniminium ion derived from a chiral secondary amine proceeded with high enantioselectivity (88 % ee).
- H?rmann, Fabian M.,Chung, Tim S.,Rodriguez, Elsa,Jakob, Matthias,Bach, Thorsten
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p. 827 - 831
(2017/12/26)
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- Br?nsted Acid Catalysis in Visible-Light-Induced [2+2] Photocycloaddition Reactions of Enone Dithianes
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1,3-Dithiane-protected enones (enone dithianes) were found to undergo an intramolecular [2+2] photocycloaddition under visible-light irradiation (λ=405 nm) in the presence of a Br?nsted acid (7.5–10 mol %). Key to the success of the reaction is presumably the formation of colored thionium ions, which are intermediates of the catalytic cycle. Cyclobutanes were thus obtained in very good yields (78–90 %). It is also shown that the dithiane moiety can be reductively or oxidatively removed without affecting the photochemically constructed ring skeleton.
- Brenninger, Christoph,P?thig, Alexander,Bach, Thorsten
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supporting information
p. 4337 - 4341
(2017/04/04)
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- Intramolecular azide-alkene 1,3-dipolar cycloaddition/enamine addition(s) cascade reaction: Synthesis of nitrogen-containing heterocycles
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A cascade intramolecular azide-alkene 1,3-dipolar cycloaddition/1,2 enamine and/or 1,4 enamine addition reaction sequence has been developed, and provides access to a variety of nitrogen containing heterocycles from readily available ω-azido alkenes. Copy
- De Miguel, Irene,Herradon, Bernardo,Mann, Enrique
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supporting information; experimental part
p. 1731 - 1736
(2012/07/28)
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- Copper-catalyzed asymmetric conjugate addition of trialkylaluminium reagents to trisubstituted enones: Construction of chiral quaternary centers
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Me3Al, Et1Al, and vinylalane species undergo enantioselective conjugate addition to a wide range of 2- or 3-substituted enones (cyclopent-2enones, cyclohex-2-enones, 3-methyl cyclohept-2-enone) in the presence of catalytic amount of copper salt (copper thiophene carboxylate, [Cu(CH3-CN)4]BF4 or [CuOTf]2· C6H6) and tropos-phosphoramidite-based ligand. Thus, chiral quaternary centers can be built, with up to 98% ee after rigorous optimization of experimental conditions. It was shown that the main important parameter was the order of the introduction of the reagents. Then, the generated enantioenriched aluminium enolates and the chiral conjugate adducts were functionalized and used for subsequent reactions.
- Vuagnoux-D'Augustin, Magali,Alexakis, Alexandre
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p. 9647 - 9662
(2008/12/21)
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- Enantioselective copper-catalyzed conjugate addition to trisubstituted cyclohexenones: Construction of stereogenic quaternary centers
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Trimethyl- and triethylaluminum undergo enantioselective conjugate addition to 3-and 2-substituted cyclohexenones in the presence of catalytic amounts of a Cu salt and a phosphoramidite ligand L* (see scheme). Thus, chiral quaternary centers can be built with up to 96.6% ee. Functionalized enones lead to bicyclic structures by a subsequent aldol reaction.
- D'Augustin, Magali,Palais, Laeticia,Alexakis, Alexandre
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p. 1376 - 1378
(2007/10/03)
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- Synthesis and biological activity of 22-oxa CD-ring modified analogues of 1α,25-dihydroxyvitamin D3: Spiro[5.5]undecane CF-ring analogues
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The synthesis and biological activity of novel CD-ring modified analogues of 22-oxa-1α,25-dihydroxyvitamin D3, lacking the D-ring and featuring a connection between C-18 and C-21 (spiro[5.5]undecane CF-ring analogues), is described. The central
- Schepens, Wim,Van Haver, Dirk,Vandewalle, Maurits,De Clercq, Pierre J.,Bouillon, Roger,Verstuyf, Annemieke
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p. 3889 - 3892
(2007/10/03)
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- Asymmetric spirocyclization: A new type of acid-catalyzed intramolecular 1,4-addition to form carba-spirocyclic compounds
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Novel spirocyclization based on intramolecular 1,4-addition and its asymmetric version have been developed using a combination of Lewis acid and 1,2-diol. Treatment of five- and six-membered α,β-unsaturated cyclic ketones having a 4-oxopentyl group at the
- Yamada, Satoshi,Karasawa, Satoru,Takahashi, Youichi,Aso, Mariko,Suemune, Hiroshi
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p. 15555 - 15566
(2007/10/03)
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- Photoreactions of Enones with Amines - Cyclization of Unsaturated Enones and Reductive Ring Opening by Photoinduced Electron Transfer (PET)
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Photolysis of the unsaturated enones 1 yields cycloaddition products 2 and 3 with varying regioselectivity.Under electron transfer conditions (PET) spirocyclic products 4 are formed.The straight cycloaddition products 2b, c, f are converted to the spirocyclic products 4b, c, f under the same reaction conditions.The cyclobutane 5 and cyclopropane 11 also undergo this new reductive ring opening reaction, while the stabilized system 7 is converted to reduced ring-enlarged triquinane 10 which may be interesting in natural product synthesis. - Irradiation of 2-cyclohexen-1-one (14) in the presence of N,N-dimethylallylamine (15) leads to the decahydroisoquinoline 18.A mechanism involving radical intermediates is discussed. Key Words: Photoinduced electron transfer / Cyclization / Ring opening / Enones
- Mattay, Jochen,Banning, Anja,Bischof, Eric W.,Heidbreder, Andreas,Runsink, Jan
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p. 2119 - 2128
(2007/10/02)
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- Stereoselective radical cyclization of epoxy silyl enol ethers
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n-Bu3Sn radical catalyzed stereoselective radical cyclization of epoxy silyl enol ethers is described.
- Kim,Koh
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p. 7391 - 7392
(2007/10/02)
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- Radical Cyclization of Epoxyketones via a 1,5-Bun3Sn Group or a 1,5-H Atom Transfer
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Radical cyclization of epoxyketones is initited by Bun3Sn radical addition to epoxyketones, followed by epoxide fragmentation, 1,5-H- or 1,5-Bun3Sn transfer, and cyclization.
- Kim, Sunggak,Koh, Jae Suk
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p. 1377 - 1378
(2007/10/02)
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- Intramolecular Addition Reactions of Carbonyl Ylides Formed during Photocyclization of Aryl Vinyl Ethers
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Photocyclization of aryl vinyl ethers reportedly proceeds via carbonyl ylide intermediates.The photochemical behavior of several aryl vinyl ethers, which incorporate a pendant alkene side chain, was explored.Naphthyl vinyl ethers 1c and 1d provided produc
- Dittami, James P.,Nie, Xiao Yi,Nie, Hong,Ramanathan, H.,Breining, Scott,et al.
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p. 5572 - 5578
(2007/10/02)
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- Organosilicon radical-induced cyclization reactions
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The first examples of selective additions of organosilicon radicals are reported. Trichlorosilyl radicals preferentially attack the carbonyl oxygen atom, while triethylsilyl radicals preferentially attack alkenes. Carbon-carbon bond formation to produce b
- Kraus, George A.,Liras, Spiros
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p. 5265 - 5268
(2007/10/02)
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- RADICAL ANIONIC CYCLIZATION REACTIONS VIA PHOTOCHEMICALLY INDUCED ELECTRON TRANSFER
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Irradiating cyclohexenones containing an olefinic side chain under electron transfer-conditions (PET) leads to new spirocyclic products 3, as well as -cycloaddition products 2.A new reductive cyclobutane ring opening allows photochemical conversion o
- Bischof, Eric W.,Mattay, Jochen
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p. 7137 - 7140
(2007/10/02)
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- Intramolecular Additions of Allylsilanes to Conjugated Dienones. The Synthesis of Three Perforanes
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Intramolecular addition of allylsilanes to 3-vinylcycloalkenones provides a powerful means of constructing functionalized 5-5, 5-7, 6-5, and 6-7 bicyclic ring systems.Our results reveal a divergence in reactivity, dependent on reaction catalyst and substr
- Majetich, George,Defauw, Jean,Ringold, Clay
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- A HIGHLY EFFICIENT SYNTHESIS OF γ- AND δ-LACTONES BY OXIDATIVE CYCLIZATION
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Treatment of tertiary γ- and δ-hydroxyolefins with pentavalent chromium reagent, (BipyH2)CrOCl5, give good yields of γ- and δ-lactones by oxidative cyclization, with loss of one carbon.Pyridinium chlorochromate (PCC) also effect this transformation to γ-lactones in reasonable yields.
- Chakraborty, T. K.,Chandrasekaran, S.
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p. 551 - 554
(2007/10/02)
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