- Umpolung of Michael acceptors catalyzed by N-heterocyclic carbenes
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N-Heterocyclic carbenes can catalyze β-alkylations of a range of α,β-unsaturated esters, amides, and nitriles that bear pendant leaving groups to form a variety of ring sizes. In this process, the nucleophilic catalyst transiently transforms the normally electrophilic β carbon into a nucleophilic site through an unanticipated addition-tautomerization sequence. Copyright
- Fischer, Christian,Smith, Sean W.,Powell, David A.,Fu, Gregory C.
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- Stereocontrolled synthesis and alkylation of cyclic β-amino esters: Asymmetric synthesis of a (-)-sparteine surrogate
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A convenient method for the stereoselective synthesis of cyclic β-amino esters from an iodo αβ-unsaturated ester and α-methylbenzylamine is described. Subsequent enolate generation and alkylation proceeds with complete stereocontrol, with the two stereogenic centres working together. In this way, a functionalised piperidine suitable for alkaloid natural product synthesis was prepared. The usefulness of the methodology is exemplified with the concise synthesis of a (-)-sparteine surrogate. The Royal Society of Chemistry.
- Hermet, Jean-Paul R.,Viterisi, Aurelien,Wright, Jonathan M.,McGrath, Matthew J.,O'Brien, Peter,Whitwood, Adrian C.,Gilday, John
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p. 3614 - 3622
(2008/09/21)
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- Concise asymmetric synthesis of (-)-sparteine
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A six-step asymmetric synthesis of natural (-)-sparteine from ethyl 7-iodohept-2-enoate is reported, involving a connective Michael addition of an amino ester-derived enolate to an α,β-unsaturated amino ester.
- Hermet, Jean-Paul R.,McGrath, Matthew J.,O'Brien, Peter,Porter, David W.,Gilday, John
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p. 1830 - 1831
(2007/10/03)
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- Asymmetric synthesis of cyclic β-amino acids
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A convenient synthesis of cyclic β-amino acid derivatives (5-, 6- and 7-rings) is achieved via a four step sequence: (i) stereoselective Michael addition of substituted α-methylbenzylamines to α,β-unsaturated chloroesters; (ii) CAN-mediated deprotection; (iii) cyclisation and (iv) α-chloroethyl chloroformate-mediated α-methylbenzylamine deprotection.
- O'Brien,Porter,Smith
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p. 1336 - 1338
(2007/10/03)
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- N-(4-methylbenzenesulfonyl)- pyrrolidines and piperidines by a tandem S(N)2-Michael addition reaction
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A tandem S(N)2-Michael addition sequence has been developed for the preparation of N-(4-methylbenzenesulfonyl)- pyrrolidines and piperidines bearing functionalized side chains at C-2.
- Bunce, Richard A.,Allison, Jeffrey C.
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p. 2175 - 2186
(2007/10/03)
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- Lithium-Halogen Exchange-Initiated Cyclization Reactions. 3. Intramolecular Conjugate Addition Reactions of Unsaturated Acylphosphoranes
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The lithium-halogen exchange-initiated intramolecular conjugate addition reactions of some model unsaturated acylphosphoranes have been examined.The effects of halide type, chain length, and acceptor substitution pattern on the feasibility of ring construction were studied.The lithium-bromine exchange reactions in two 2-bromooaryl acceptors were found to be too slow, relative to competing side reactions, to allow practical carbocycle syntheses while 3-,4-,5-, and 6-membered carbocycles are formed in good to excellent yields from precursors that are vinyl and saturated primary iodides.Highly efficient intramolecular conjugate addition reactions to β,β-disubstituted acceptor units are possible, and intermediate anions from intramolecular conjugate addition reactions are readily captured with electrophiles.
- Cooke, Manning P.,Widener, Rexford K.
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p. 1382 - 1396
(2007/10/02)
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