Stereoselective Synthesis of <i>trans</i> β-Lactams through Iridium-Catalyzed Reductive Coupling of Imines and Acrylates

Townes, Jennifer A.; Evans, Michael A.; Queffelec, Jerome; Taylor, and Steven J.; Morken, James P.

doi:10.1021/ol020106u

Cited by 73 publications

(32 citation statements)

References 19 publications

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“…The benzylic lithiation of substituted acrylamides bearing a b-electron-withdrawing group, followed by 4-exo-trig cyclization, has yielded b-lactams in modest yields [95]. Iridium-catalyzed reductive coupling of acrylates and imines provides trans b-lactams 36 with high diastereoselection (Scheme 24.21) [96]. The optimal catalyst allows for the synthesis of trans b-lactams bearing aromatic, alkenyl and alkynyl side chains.…”

Section: Miscellaneousmentioning

confidence: 99%

The Chemistry of 2‐Azetidinones (β‐Lactams)

Alcaide¹,

Almendros²,

Luna³

2011

Modern Heterocyclic Chemistry

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The large number of recent reports on b-lactam chemistry demonstrates the increasing interest in this important class of compounds. Monocyclic b-lactams frequently serve as precursors for the synthesis of classical bicyclic b-lactam antibiotics. The cyclic 2-azetidinone skeleton has been extensively used as a template on which to build the heterocyclic structure fused to the four-membered ring, using the chirality and functionalization of the b-lactam nucleus as a stereocontrolling element. The discovery of nonclassical b-lactam antibiotics, such as monobactams and nocardicins, coupled with ever-growing new applications such as enzyme inhibition has triggered a renewed interest in the building of new monocyclic b-lactam derivatives. Besides the utility of b-lactams as biologically active agents, they are used as intermediates in a-and b-amino acid synthesis, as well as building blocks for alkaloids, heterocycles, taxoids and other types of compounds of biological and medicinal interest. Physicochemical Data Computational ChemistryTheoretical studies show that b-lactams are weaker bases, in the gas phase, than acyclic amides [1]. The attenuation of basicity upon cyclization is stronger than that found for cyclic ketones of similar size due to the existence of a negative hyperconjugation effect that is present in b-lactams but not in cyclic ketones. Ab initio calculations indicate that both b-lactams and acyclic amides are oxygen bases, but the gap between the oxygen and nitrogen intrinsic basicities is much smaller in the former due to the aforementioned cyclization effects. This decrease of the oxygen Modern Heterocyclic Chemistry, First Edition. Edited

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Section: Miscellaneousmentioning

confidence: 99%

The Chemistry of 2‐Azetidinones (β‐Lactams)

Alcaide¹,

Almendros²,

Luna³

2011

Modern Heterocyclic Chemistry

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“…a,b-Unsaturated carbonyl compounds are known to participate in reductive Mannich couplings mediated by silane [121,122] and the Hantzsch ester [123]. Completely by-product-free reductive Mannich couplings are potentially achieved using elemental hydrogen as the terminal reductant.…”

Section: Hydrogenative Aldol and Mannich Additionsmentioning

confidence: 99%

Hydrogenation for C  C Bond Formation

Bower

Krische

2010

Handbook of Green Chemistry

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The formation of chemical bonds between carbon atoms is of fundamental significance. A major goal in the emerging field of green chemistry involves the design of by-product-free chemical processes, especially CÀC bond-forming processes applicable to renewable feedstocks [1]. This objective is aligned with longstanding economic and aesthetic forces that have shaped the field of chemical synthesis and which have given rise to such concepts as atom-economy [2], step-economy and the ideal synthesis [3]. As revealed by the E-factor (kilogram of waste generated per kilograms of product) [4], it is not surprising that an inverse correlation between process volume and waste generation exists in the chemical industry. For largevolume processes, where minute improvements in efficiency confer significant economic return, by-product-free chemical processes are desirable as they mitigate costs associated with waste disposal and product isolation. Here, fiscal natural selection mandates the practice of green chemistry. In contrast, the fine chemical and pharmaceutical industrial segments often engage in multi-step syntheses where the value of late-stage intermediates can easily exceed the cost of waste stream disposal or product separation, undermining motivation to develop by-product-free protocols (Table 8.1).Must waste production generally increase with increasing molecular complexity? What transformations would be practiced on a vast scale if only efficient by-productfree variants were developed? In the specific case of CÀC bond-forming processes, especially those involving non-stabilized carbanions and their equivalents, a significant cause of waste production resides in the use of stoichiometrically preformed organometallic reagents, which give rise to equimolar quantities of chemical byproducts in the form of metal salts. For example, the vinylation and allylation of carbonyl compounds and imines, which are core reactions in synthetic organic chemistry, uniformly employ preformed vinylmetal and allylmetal reagents. The Green Catalysis, Volume 1: Homogeneous Catalysis. Edited by Robert H. Crabtree

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“…295). 476 The conversion of an ethyl ynoate into an E-ethyl enoate in high yield is shown in Eq. 296 …”

Section: Reduction Of αβ-Unsaturated Estersmentioning

confidence: 99%