10. Patented Literature 2616 10.1. Esterification 2616 10.2. Ether Formation 2619 10.2.1. Etherification without Cyclization 2619 10.2.2. Etherification with Cyclization 2624 10.3. N-Alkylation 2625 10.4. Other Reactions 2627 11. Summary and Outlook 2628 12. Note Added in Proof 2628 13. Abbreviations Used in This Review 2629 14. Acknowledgments 2629 15. Supporting Information Available 2630 16. References 2630

Mitsunobu and Related Reactions: Advances and Applications

The mechanism of the Wittig reaction has long been a contentious issue in organic chemistry. Even now, more than 50 years after its announcement, its presentation in many modern undergraduate textbooks is either overly simplified or entirely inaccurate. In this review, we gather together the huge body of evidence that has been amassed to show that the Li salt-free Wittig reactions of non-stabilised, semi-stabilised and stabilised ylides all occur under kinetic control by a common mechanism in which oxaphosphetane (OPA) is the first-formed and only intermediate. The numerous recent significant additions to the subject – including computational studies and experimental material pertinent to both steps of the reaction (OPA formation and its decomposition) are discussed in detail, and the currently accepted explanations for the source of the stereoselectivity in Wittig reactions are given. We also present the other mechanistic proposals that have been made during the history of the Wittig reaction, and show how they are unable to account for all of the experimental evidence that is now available. Details of certain experimental facts to do with Wittig reactions in the presence of Li cation are also included, although the precise mechanistic details of such reactions are yet to be established conclusively. We make the case that a clear distinction should henceforth be made between the unknown “Li-present” and the now well-established “Li salt-free” Wittig mechanisms.

/pdf/the-modern-interpretation-of-the-wittig-reaction-mechanism-2yo1sx00p1.pdf

The modern interpretation of the Wittig reaction mechanism

Nitrogen‐, and/or Sulfur-Containing Heterocyclic Rings Poulomi Majumdar,†,‡ Anita Pati,†,§ Manabendra Patra, Rajani Kanta Behera,† and Ajaya Kumar Behera*,† †Organic Synthesis Laboratory, School of Chemistry, Sambalpur University, Jyoti Vihar, Burla 768019, Orissa, India ‡State Key Laboratory of Fine Chemicals, School of Chemical Engineering, Dalian University of Technology, Dalian, 116024, P.R. China School of Applied Sciences (Chemistry), KIIT University, Bhubaneswar 751024, India National Institute of Science & Technology, Palur Hill, Berhampur 761068, Orissa, India

Acid hydrazides, potent reagents for synthesis of oxygen-, nitrogen-, and/or sulfur-containing heterocyclic rings.

A series of N,N‘-disubstituted ureas having a conformationally restricted cis- or trans-1,4-cyclohexane α to the urea were prepared and tested as soluble epoxide hydrolase (sEH) inhibitors. This series of compounds showed low nanomolar to picomolar activities against recombinant human sEH. Both isomers showed similar potencies, but the trans isomers were more metabolically stable in human hepatic microsomes. Furthermore, these new potent inhibitors show a greater metabolic stability in vivo than previously described sEH inhibitors. We demonstrated that trans-4-[4-(3-adamantan-1-ylureido)cyclohexyloxy]benzoic acid 13g (t-AUCB, IC50 = 1.3 ± 0.05 nM) had excellent oral bioavailability (98%, n = 2) and blood area under the curve in dogs and was effective in vivo to treat hypotension in lipopolysaccharide challenged murine models.

/pdf/orally-bioavailable-potent-soluble-epoxide-hydrolase-41aof0i3mw.pdf

Orally bioavailable potent soluble epoxide hydrolase inhibitors.

The nucleophilic addition of carbon nucleophiles to amides has traditionally been a difficult task, both due to reactivity and selectivity problems. When successful, these processes would represent straightforward routes towards carbonyl-type or amine compounds, depending on the fate of the generated tetrahedral intermediate. The direct addition of nucleophiles to amides for the preparation of ketones has been studied and applied to the syntheses of several natural products. On the other hand, the addition of nucleophiles to amides to obtain substituted amines represented a major challenge, and only scattered applications on particular substrates have appeared. Initial improvements were based on the activation of amides by introduction of particular substituents, such as in N-methoxy amides (Weinreb amides) or electron-withdrawing groups able to increase the carbon nucleophilicity. Although these strategies facilitate the introduction of nucleophiles, chemoselectivity issues arise when additional electrophilic moieties (i.e., carbonyls) are present, thus decreasing the versatility of the methods. In recent years, important advancements towards fully chemoselective methods have been realized. The capture of tetrahedral intermediates with acids generates highly electrophilic iminium species able to undergo chemoselective additions of various nucleophiles, thus accessing substituted amines. Alternatively, the in situ generation of an iminium triflate ion allows highly chemoselective additions of nucleophiles, yielding amines, ketones or ketimines. Also thioamides can be used as precursors of ketones or alpha-substituted amines. The success of the above methodologies is further showcased by the application in various syntheses of natural products or biologically active molecules.

Increasing the Reactivity of Amides towards Organometallic Reagents: An Overview

Direct Conversion of N-Methoxy-N-methylamides (Weinreb Amides) to Ketones via a Nonclassical Wittig Reaction

N-Methoxy-N-methylamides (Weinreb amides) are converted efficiently into ketones by reaction with alkylidenetriphenylphosphoranes and in situ hydrolysis of the product.

Direct Conversion of N-Methoxy-N-methylamides (Weinreb Amides) to Ketones via a Nonclassical Wittig Reaction.

Reactions of Weinreb amides: formation of aldehydes by Wittig reactions

Synthesis of Muscothiazoles A and B: Critical Role of Methyl Group Substitution in RCM-Based Syntheses of Macrocycles

Muscothiazoles A (2b) and B (2c) have been prepared by two approaches that differ in the order of assembly of the rings. Comparative studies show that substitution of the carbon chains in substrate 5 or 12 (respective precursors to 13-membered and 14-membered rings by RCM), even by a single methyl group, can have a profound effect on increasing the efficiency of the macrocyclization.

/pdf/synthesis-of-muscothiazoles-a-and-b-critical-role-of-methyl-2zwrabiclv.pdf

Synthesis of Muscothiazoles A and B: Critical Role of Methyl Group Substitution in RCM‐Based Syntheses of Macrocycles.

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