- A mechanistic study of the Lewis base-directed cycloaddition of 2-pyrones and alkynylboranes
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Significant rate enhancements in the Diels-Alder reaction of alkynes and 2-pyrones bearing a Lewis basic group are observed when a combination of alkynyltrifluoroborates and BF3·OEt2 is used. This process generates functionalized aromatic compounds with complete regiocontrol. The observed rate enhancement was studied by density functional theory methods and appears to originate from coordination of the diene substrate to a mixture of alkynylborane intermediates, followed by a Lewis acid-mediated product equilibration step. Evidence for this mechanism is presented, as is the enhanced promotion of the cycloaddition via the use of alternative Lewis acid promoters.
- Crépin, Damien F.P.,Harrity, Joseph P.A.,Jiang, Julong,Meijer, Anthony J.H.M.,Nassoy, Anne-Chloé M.A.,Raubo, Piotr
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- Lewis base directed cycloaddition reactions of 2-pyrones and alkynylaluminum reagents
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In situ generated alkynylaluminum reagents have been utilized in a [4 + 2] cycloaddition with 2-pyrones bearing a Lewis basic donor. The reactions proceed at or below room temperature and with complete regiocontrol. This one-pot method affords diversely s
- Crepin, Damien F.,Harrity, Joseph P. A.
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supporting information
p. 4222 - 4225
(2013/09/12)
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- A mild benzannulation through directed cycloaddition reactions
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Simple as ABC: Alkynyl borane cycloadditions can be substrate-directed to assemble aromatic difluoroboranes within an extremely mild and efficient reaction manifold compared to that of traditional methods (see scheme). The aromatic boranes are readily transformed into a range of useful products. Copyright
- Kirkham, James D.,Butlin, Roger J.,Harrity, Joseph P. A.
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supporting information; experimental part
p. 6402 - 6405
(2012/07/28)
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- A designed synthetic analogue of 4-OT is specific for a non-natural substrate
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The substrate specificity of 4-oxalocrotonate tautomerase (4-OT) is characterized by electrostatic interactions between positively charged arginine (Arg) side chains on the enzyme and the dianionic substrate, 4-oxalocrotonate. To generate specific hydrogen-bonding interactions with a monoanionic substrate analogue, we have introduced a urea functional group into the active site by replacing arginine side chains with isosteric citrulline (Cit) residues. This design was based on the complementarity between the urea functionality of citrulline and the uncharged amide function of the substrate, as opposed to the guanidinium-carboxylate electrostatic interaction between the wild-type enzyme and the natural substrate. Indeed, the synthetic (Arg39Cit)4-OT analogue catalyzed the tautomerization of the non-natural monoamide-monoacid substrate while it was a poor catalyst for the natural diacid substrate. The specificity of (Arg39Cit)4-OT for the monoamide-monoacid substrate relative to that of the diacid substrate was found to be 740-fold greater than that of the wild-type enzyme for tautomerization of the non-natural substrate as compared with the natural one. The role of electrostatic interactions in the tautomerization of the monoamide-monoacid substrate was probed in detail with several other Arg to Cit analogues of this enzyme. This study has demonstrated that chemical manipulation of the functional groups within the active site of an enzyme can modify its catalytic activity and substrate specificity in a predictable way, suggesting that the incorporation of noncoded amino acids into proteins has great promise for the development of new enzymatic mechanisms and new binding interactions.
- Metanis, Norman,Keinan, Ehud,Dawson, Philip E.
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p. 5862 - 5868
(2007/10/03)
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- THE QUEEN RECOGNITION PHEROMONE OF SOLENOPSIS INVICTA, PREPARATION OF (E)-6-(1-PENTENYL)-2H-PYRAN-2-ONE.
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The title compound, I, prepared in five steps via four known α-pyrones, is responsible, in part, for "queen recognition" by red imported fire ant workers.IR, NMR and MS data are presented.
- Rocca, J. R.,Tumlinson, J. H.,Glancey, B. M.,Lofgren, C. S.
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p. 1889 - 1892
(2007/10/02)
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