- Palladium-catalyzed ring-closing reaction via C-N bond metathesis for rapid construction of saturated N-heterocycles
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The ring-closing reactions based on chemical bond metathesis enable the efficient construction of a wide variety of cyclic systems which receive broad interest from medicinal and organic communities. However, the analogous reaction with C-N bond metathesis as a strategic fundamental step remains an unanswered challenge. Herein, we report the design of a new fundamental metallic C-N bond metathesis reaction that enables the palladium-catalyzed ring-closing reaction of aminodienes with aminals. The reactions proceed efficiently under mild conditions and exhibit broad substrate generality and functional group compatibility, leading to a wide variety of 5- to 16-membered N-heterocycles bearing diverse frameworks and functional groups.
- Yu, Bangkui,Zou, Suchen,Liu, Hongchi,Huang, Hanmin
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- Intramolecular Hydroamination/Cyclization of Conjugated Aminodienes Catalyzed by Organolanthanide Complexes. Scope, Diastereo- and Enantioselectivity, and Reaction Mechanism
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Organolanthanide complexes of the general type Cp′ 2LnCH(TMS)2 (Cp′ = η5-Me 5C5; Ln = La, Sm, Y; TMS = SiMe3) and CGCSmN(TMS)2 (CGC = Me2Si(η5-Me 4C5)(tBuN)) serve as effective precatalysts for the rapid, regioselective, and highly diastereoselective intramolecular hydroamination/cyclization of primary and secondary amines tethered to conjugated dienes. The rates of aminodiene cyclizations are significantly more rapid than those of the corresponding aminoalkenes. This dienyl group rate enhancement as well as substituent group (R) effects on turnover frequencies is consistent with proposed transition state electronic demands. Kinetic and mechanistic data parallel monosubstituted aminoalkene hydroamination/cyclization, with turnover-limiting C=C insertion into the Ln-N bond to presumably form an Ln-η3 allyl intermediate, followed by rapid protonolysis of the resulting Ln-C linkage. The rate law is first-order in [catalyst] and zero-order in [aminodiene]. However, depending on the particular substrate and catalyst combination, deviations from zero-order kinetic behavior reflect competitive product inhibition or self-inhibition by substrate. Lanthanide ionic radius effects and ancillary ligation effects on turnover frequencies suggest a sterically more demanding Ln-N insertion step than in aminoalkene cyclohydroamination, while a substantially more negative ΔS? implies a more highly organized transition state. Good to excellent diastereoselectivity is obtained in the synthesis of 2,5-trans-disubstituted pyrrolidines (80% de) and 2,6-cis-disubstituted piperidines (99% de). Formation of 2-(prop-1-enyl)piperidine using the chiral C1-symmetric precatalyst (S)-Me2Si(OHF)(CpR* )SmN(TMS)2 (OHF = η5-octahydrofluorenyl; Cp = η5-C5H3; R* = (-)-menthyl) proceeds with up to 71% ee. The highly stereoselective feature of aminodiene cyclization is demonstrated by concise syntheses of naturally occurring alkaloids, (±)-pinidine and (+)-coniine from simple diene precursors.
- Hong, Sukwon,Kawaoka, Amber M.,Marks, Tobin J.
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p. 15878 - 15892
(2007/10/03)
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