- Intramolecular 1,3-dipolar cycloadditions of dihydroimidazolium ylides: Synthesis of pyrrolo[1,2,3-de]quinoxalines and imidazo[1,2-a]indoles
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N-Alkylation of 4,5-dihydroimidazoles with alkene-containing bromomethyl ketones and treatment of the so-formed 4,5-dihydroimidazolium ions with DBU gives rise to an intramolecular 1,3-dipolar cycloaddition reaction that affords (via a reaction cascade involving eliminative ring-opening, recyclisation and prototropic tautomerism) unexpected hexahydropyrrolo[1,2,3-de]quinoxaline products. Steric bulk in both the dihydroimidazole and the dipolarophile allows isolation of an imidazo[1,2-a]indole, the initial product of cycloaddition. When the bromomethyl ketone contains no other functionality, or when cycloaddition is inhibited due to steric constraints, the dihydroimidazolium ion undergoes ring-opening hydrolysis followed by recyclization of the exposed amino ketone to afford either 3-alkyl-1-formylpiperazine-2-ones or 3-aryl-1-formyl-1,4,5,6- tetrahydropyrazines. The Royal Society of Chemistry 2006.
- Lory, Pedro M.J.,Jones, Raymond C.F.,Iley, James N.,Coles, Simon J.,Hursthouse, Michael B.
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p. 3155 - 3165
(2008/03/12)
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- Pyrrolo[1,2,3-de]quinoxalines: Unexpected products from 1,3-dipolar cycloaddition of dihydroimidazolium ylides
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4,5-Dihydroimidazoles undergo an N-alkylation and 1,3-dipolar cycloaddition cascade with unsaturated α-bromoketones, with subsequent eliminative ring-opening, recyclisation and tautomerisation to form unexpected hexahydropyrrolo[1,2,3-de]quinoxalines.
- Jones, Raymond C.F,Iley, James N.,Lory, Pedro M.J.,Coles, Simon C.,Light, Mark E.,Hursthouse, Michael B.
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p. 3951 - 3954
(2007/10/03)
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- Syntheses of α,β-unsaturated carbonyl compounds from the reactions of monosubstituted ozonides with stable phosphonium ylides
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Ozonides derived from terminal alkenes reacted with 1.3 mol equiv. of stable phosphonium ylides to give (E)-αβ-unsaturated carbonyl compounds in good to excellent yields. No reducing agent is needed in the reaction. However, alkoxyalkyl-substituted ozonides afforded a mixture of (Z)- and (E)-αβ-unsaturated carbonyl compounds under similar condition. The E/Z isomeric ratio is affected by the position of the heteroatom in the substituent of the ozonides. The possible mechanism of this reaction will be discussed. (C) 2000 Elsevier Science Ltd.
- Hon, Yung-Son,Lu, Ling,Chang, Rong-Chi,Lin, Sheng-Wun,Sun, Pei-Pei,Lee, Chia-Fu
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p. 9269 - 9279
(2007/10/03)
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- Intramolecular Michael addition of N- and O-centred nucleophiles to tethered acrylates. The role of double-bond geometry in controlling the diastereoselectivity of cyclizations teading to 2,6-disubstituted tetrahydropyrans and piperidines
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The oxyanion derived from hydroxyacrylate E-(5) undergoes smooth intramolecular Michael addition to give the trans-2,6-disubstituted tetrahydropyran (7) as the major product of reaction. In contrast, the oxyanion obtained from isomer Z-(5) cyclizes to give the cis-2,6-disubstituted tetrahydropyran (6) as the major product. Such chemistry has been extended to the enantioselective synthesis of (+)-(6) the acquisition of which constitutes a formal total synthesis of acid (+)-(2), a constituent of the glandular secretion from the civet cat (Viverra civetta). Reductive amination of keto acrylate (12) affords an intermediate amine which cyclizes, in situ, to give the cis-2,6-disubstituted piperidine (26). Analogous treatment of compound (13) delivers the isomeric trans-2,6-disubstituted piperidine (27) as the exclusive product of reaction. Transition state structures have been proposed to account for the diastereoselectivities observed in all of the cyclization reactions.
- Banwell, Martin G.,Bissett, Brett D.,Bui, Chinh T.,Pham, Ha T.T.,Simpson, Gregory W.
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- X = Y - ZH systems as potential 1,3-dipoles part 35. Generation of nitrones from oximes. Class 3 processes. Tandem intramolecular Michael addition (1,3-azaprotio cyclotransfer) - Intermolecular 1,3-dipolar cycloaddition reactions
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Aldoximes and ketoximes possessing γ- or δ-alkenyl substituents undergo thermal conversion to 5-and 6- membered cyclic nitrones via a 1,3-azaprotio cyclotransfer, a 2n + 2oσ + 2π concerted process, rather than a Michael addition. The reactions can be performed as a tandem nitrone formation-cycloaddition sequence or, if required, the intermediate nitrones can be isolated. The cycloadditions usually proceed via an exo-transition state and show both regio- and diastereofacial-specificity. Preliminary attempts at chiral induction via a menthyl auxiliary are reported.
- Grigg, Ronald,Markandu, Jasothara,Perrior, Trevor,Surendrakumar, Sivagnanasundram,Warnock, William J.
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p. 6929 - 6952
(2007/10/02)
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- The Reaction of Ozonides from Mono-substituted Alkenes with Stabilized Phosphorus Ylides
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Ozonides derived from mono-substituted alkenes react with methyl (triphenylphosphoranylidene)acetate or (triphenylphosphoranylidene)acetophenone to form trans-α,β-unsaturated esters or ketones, respectively, in high yields.
- Hon, Yung-Son,Lu, Ling,Li, Shyh-Yuan
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p. 1627 - 1628
(2007/10/02)
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