Sequential Reactions Promoted by Manganese: Completely Stereoselective Synthesis of (E)-α,β-Unsaturated Amides, Ketones, Aldehydes, and Carboxylic Acids

Seeing Is Not Necessarily Believing: Is the Surface-Enhanced Raman Spectroscopy Signal Really from the Target?

Reagent purity is crucial to experimental research, considering that the ignorance of ultratrace impurities may induce wrong conclusions in either revealing the reaction nature or qualifying the target. Specifically, in the field of surface science, the strong interaction between the impurity and the surface will bring a non-negligible negative effect. Surface-enhanced Raman spectroscopy (SERS) is a highly surface-sensitive technique, providing fingerprint identification and near-single molecule sensitivity. In the SERS analysis of trace chloromethyl diethyl phosphate (DECMP), we figured out that the SERS performance of DECMP is significantly distorted by the trace impurities from DECMP. With the aid of gas chromatography-based techniques, one strongly interfering impurity (2,2-dichloro-N,N-dimethylacetamide), the byproduct during the synthesis of DECMP, was confirmed. Furthermore, the nonignorable interference of impurities on the SERS measurement of NaBr, NaI, or sulfadiazine was also observed. The generality ignited us to refresh and consolidate the guideline for the reliable SERS qualitative analysis, by which the potential misleading brought by ultratrace impurities, especially those strongly adsorbed on Au or Ag surfaces, could be well excluded.

Enantioselective Synthesis of Tertiary β‐Boryl Amides by Conjunctive Cross‐Coupling of Alkenyl Boronates and Carbamoyl Chlorides

Synthesis of versatile β tert-boryl amides is accomplished by conjunctive cross-coupling of α-substituted alkenyl boron "ate" complexes and carbamoyl chloride electrophiles. This reaction can be accomplished in an enantioselective fashion using a palladium catalyst in combination with MandyPhos. The addition of water results in enhanced chemoselectivity for the conjunctive coupling product relative to the Suzuki-Miyaura cross-coupling product. Transformations of the reaction products were examined as well as application to the synthesis of (+)-adalinine.

Manganese(I) Catalyzed α-Alkenylation of Amides Using Alcohols with Liberation of Hydrogen and Water

Herein, unprecedented manganese-catalyzed direct α-alkenylation of amides using alcohols is reported. Aryl amides are reacted with diverse primary alcohols, which provided the α,β-unsaturated amides in moderate to good yields with excellent selectivity. Mechanistic studies indicate that Mn(I) catalyst oxidizes the alcohols to their corresponding aldehydes and also plays an important role in efficient C═C bond formation through aldol condensation. This selective olefination is facilitated by metal-ligand cooperation by the aromatization-dearomatization process operating in the catalytic system. Biorenewable alcohols are used as alkenylation reagents for the challenging α-alkenylation of amides with the highly abundant base metal manganese as a catalyst, which results in water and dihydrogen as the only byproduct, making this catalytic transformation attractive, sustainable, and environmentally benign.

Synthesis of β-Fluoro-α,β-Unsaturated Amides from the Fragmentation of Morpholine 3,3,3-Trifluoropropanamide by Grignard Reagents

Fluoroalkenes serve as bioisosteres to peptide bonds and are resistant to hydrolytic enzymes in vivo. Currently, α-fluoro-α,β-unsaturated carbonyl compounds are readily accessible via general synthetic methods; however, β-fluoro-α,β-unsaturated carbonyl groups are more challenging to construct. To address this need, we have designed a reagent, morpholine 3,3,3-trifluoropropanamide, that creates (E)-β-fluoro-α,β-unsaturated amides upon the addition of many commonly used Grignard reagents. Reactions with this reagent enable a high level of stereocontrol in the fluoroalkene product.

Stereoselective three-component cascade synthesis of α-substituted 2,4-dienamides from gem-difluorochloro ethanes

Herein, we describe a new transition metal-free Claisen rearrangement for the synthesis of α-substituted 2,4-dienamides. The one-pot, stereoselective three-component cascade reaction between a series of propargyl alcohols, amines, and gem-difluorochloro ethane derivatives afforded various polysubstituted 2,4-dienamides in good yields. This synthetic method for 1,1-captodative dienes, α-substituted 2,4-dienamides, can be utilized for preparing pharmaceutical analogues containing an indolin-2-one or lactone moiety.

Lewis-Base-Catalyzed Reductive Aldol Reaction To Access Quaternary Carbons

A synthetic method for the efficient construction of β-hydroxylactones and lactams bearing α-quaternary carbon centers is described. This transformation relies on an electronically differentiated Lewis base catalyst, which is uniquely capable of promoting a reductive aldol reaction of α,α-disubstituted and α,α,β-trisubstituted enones. This approach provides a valuable synthetic alternative for carbon-carbon bond formation in complex molecular settings due to its orthogonal reactivity compared to that of traditional aldol reactions. Based on this method described herein, lactones, lactams, and morpholine amides bearing α-quaternary carbon centers are accessible in yields up to 85% and 50:1 dr.

Titanium-Promoted Cross-Coupling for the Selective Synthesis of Polysubstituted, Conjugated Amides

α,β-Unsaturated amides are important building blocks and are key structural elements in a number of biologically active natural products. Despite their importance and prevalence, few methods exist to prepare conjugated amides directly and modularly. To address this gap, a titanium-promoted coupling of alkynes and isocyanates has been developed. The method is highly stereoselective, producing only the E isomer with good chemoselectivity and regioselectivity (>95/5), for unsymmetrical internal alkynes that contain a steric bias. The reactive titanacyclopentene intermediate formed from the coupling of the alkyne and isocyanate was additionally reacted with various electrophiles to access tetrasubstituted enamides.

Synthesis of α,β-Unsaturated N-Sulfonyl Imides through Zinc-Catalyzed Intermolecular Oxidation of N-Sulfonyl Ynamides

A novel zinc-catalyzed intermolecular oxidation of N-sulfonyl ynamides has been developed. A variety of functionalized α,β-unsaturated N-sulfonyl imides are readily accessed by utilizing this approach, thus providing a viable alternative to synthetically useful α,β-unsaturated imides. Importantly, the reaction is proposed to proceed by a vinyligous E2-type elimination pathway, but not metal carbene pathway.

Column chromatography-free solution-phase synthesis of a natural piper-amide-like compound library

We have achieved an efficient solution-phase parallel synthesis of a library of natural piper-amide-like compounds from the bifunctional β-phosphono-N-hydroxy-succinimidyl ester intermediate. The primary important feature in our study is the construction of natural-product-like molecules through the adaptation of sophisticated organic reactions that create water-soluble byproducts for a chromatography-free purification. This simple and efficient method rapidly provides a combinatorial library of high yield and purity. The library was evaluated against GPCR targets to demonstrate its potential use as a tool for drug discovery and in chemical biology.

Site-specific introduction of gold-carbenoids by intermolecular oxidation of ynamides or ynol ethers

Ynamides and ynol ethers undergo intermolecular gold-catalysed reaction with a nucleophilic oxidant to access metal-carbenoid reactivity patterns. A site-specific oxidation/1,2-insertion cascade is used for a general access to functionalised α,β-unsaturated carboxylic acid derivatives and vinylogous carbimates.

Indium-Mediated Microwave-Assisted One-Pot Synthesis of α,β-Unsaturated Amides

A stereoselective synthesis of α,βunsaturated-N,N-diethyl amides was achieved by a one-pot reaction of triphenylphosphine, an aromatic aldehyde, and N,N-diethyl chloroacetamide in the presence of indium under microwave-assisted and solvent-free condition.

Microwave-assisted one-pot synthesis of a, β-unsaturated amides under solvent-free conditions

Under microwave-assisted solvent-free conditions a one-pot reaction of triphenylphosphine, an aldehyde and N, N-diethyl chloroacetamide in the presence of zinc dust affords α, β-unsaturated amides stereoselectively in good yield. In comparison with the conventional heating method, the reaction was finished within five minutes under microwave irradiation.

Recent synthetic applications of manganese in organic synthesis

While the organometallic compounds derived from many metals have found a broad application in organic synthesis, the use of organomanganese compounds has only recently been developed due to the passivity exhibited by commercial Mn in the direct metalation of organic compounds. In this Concept article, we highlight the potential of manganese and its organometallic compounds in organic synthesis by illustration of the studies previously reported by others and our laboratory in this field. Based on the transformations reported herein, organomanganese compounds could become important tools in the future of the organic synthesis, due to their high selectivity.

Stereocontrolled synthesis of Z-dienes via an unexpected pericyclic cascade rearrangement of 5-amino-2,4-pentadienals

Donor-acceptor dienes known as Zincke aldehydes, which derive readily from the ring-opening reactions of pyridinium salts with secondary amines, undergo a fascinating thermal rearrangement reaction to afford Z-alpha,beta,gamma,delta-unsaturated amides with excellent stereoselectivity. Efficient, stereocontrolled access to Z-trisubstituted alkenes with two different substitution patterns is possible in three steps beginning with the appropriately substituted pyridine derivative. Preliminary studies have shown that both the amide and the monosubstituted alkene termini can be selectively functionalized. Ease of access, generality of scope, and facile product manipulation render this process attractive for the synthesis of complex polyenes.

Stereoselective synthesis of (Z)-alpha-halo-alpha,beta-unsaturated esters, and amides from aldehydes and trihaloesters or amides promoted by manganese

Preliminary results of a Mn-promoted sequential process directed toward the stereoselective synthesis of different (Z)-alpha-halo-alpha,beta-unsaturated compounds are described.