Synergistic Relay Reactions To Achieve Redox‐Neutral α‐Alkylations of Olefinic Alcohols with Ruthenium(II) Catalysis

Organobase-Catalyzed Umpolung of Amides: The Generation and Transfer of Carbamoyl Anion

A novel organobase-catalyzed umpolung reaction of amides was disclosed. This method provides an efficient method to generate and transfer carbamoyl anions. In this transformation, some of the inherent disadvantages of carbamoyl metal were avoided. The mechanistic analysis revealed that the reaction proceeds through polarity inversion of amide, and various carbamoyl anions were applied in the reaction. Moreover, a wide range of substrates was achieved with moderate to excellent yield.

HOME-Chemistry: hydrazone as organo-metallic equivalent

The modern synthetic chemistry heavily relies on the use of stoichiometric organometallic reagents to react with various electrophiles. The dependence on stoichiometric quantities of metals and often organic halides as precursors, in turn both produces copious amounts of metal halide wastes as well as leads to concerns on future metal sustainability. Inspired by the classical Wolff-Kishner reduction, our lab has recently developed a general strategy of HOME-Chemistry , directly using naturally abundant alcohols/aldehydes and ketones as feedstocks with the releasing of innocuous water and nitrogen gas. These reactions include 1,2-carbonyl/imine addition, conjugate addition, carboxylation, olefination, cross-coupling arylation/allylation, alkylation, hydroalkylation and C-heteroatom formations. This article provides a brief summary on this chemistry.

Nickel-Catalyzed Stereoselective Alkenylation of Ketones Mediated by Hydrazine

The direct conversion of naturally abundant carbonyl compounds provides a powerful platform for the efficient synthesis of valuable chemicals. In particular, the conversion of ketones to alkenes is a commonly encountered chemical transformation, often achieved via the multistep Shapiro reaction with tosylhydrazone and over stoichiometric organolithium or Grignard reagent. Herein, we report an earth abundant nickel-catalyzed alkenylation of naturally abundant methylene ketones to afford a wide range of alkene derivatives, mediated by hydrazine. The protocol features a broad substrate scope (including alkyl ketones, aryl ketones, and aldehydes), good functional group compatibility, mild reaction conditions, water tolerance, and only environmentally friendly N₂, H₂, and H₂O as theoretical byproducts. Moreover, gram-scale synthesis with good yield and generation of pharmaceutical intermediates highlighted its practical applicability.

Carbon–carbon bond formation and green chemistry: one dream and 30 years hence

Carbon–carbon bond formation is the core of organic synthesis, in which organometallic reagents play the key role in the forms of 1,2-nucleophilic additions, conjugate additions, and transition-metal catalyzed cross-couplings. These reactions have enabled the production of a wide range of organic molecules in our society. Despite the enormous power of organometallic reagents in chemical synthesis, they have inherent drawbacks in the eyes of future sustainability. This account summarizes our efforts over the past three decades on the exploration of new scientific means to overcome the drawbacks and limitations of these classical organometallic reactions.

Deoxygenative Functionalizations of Aldehydes, Ketones and Carboxylic Acids

Conversion of carbonyl compounds, including aldehydes, ketones and carboxylic acids, into functionalized alkanes via deoxygenation would be highly desirable from a sustainability perspective and very enabling in chemical synthesis. This review covers the recent methodology development in carbonyl and carboxyl deoxygenative functionalizations, highlighting some typical and significant contributions in this field. These advances will be categorized based on types of bond formation, and in each part, selected examples will be discussed from their generalized mechanistic perspectives. Four summarized reactivity modes of aldehydes and ketones during the deoxygenation, namely, bis-electrophile, carbenoid, bis-nucleophile and alkyl radical, are presented, while the carboxylic acids are deoxygenated mainly via activated carbonyl or acetal intermediates.

Copper-Catalyzed Conjugate Addition of Carbonyls as Carbanion Equivalent via Hydrazones

Copper-catalyzed conjugate addition is a classic method for forming new carbon-carbon bonds. However, copper has never showed catalytic activity for umpolung carbanions in hydrazone chemistry. Herein, we report a facile conjugate addition of hydrazone catalyzed by readily available copper complexes at room temperature. The employment of mesitylcopper(I) and electron-rich phosphine bidentate ligand is a key factor affecting reactivity. The reaction allows various aromatic hydrazones to react with diverse conjugated compounds to produce 1,4-adducts in yields of about 20 to 99%.

Carbonyl umpolung as an organometallic reagent surrogate

Construction of new carbon-carbon bonds is the cornerstone of organic chemistry. Organometallic reagents are amongst the most robust and versatile nucleophiles for this purpose. Polarization of the metal-carbon bonds in these reagents facilitates their reactions with a vast array of electrophiles to achieve chemical diversification. The dependence on stoichiometric quantities of metals and often organic halides as feedstock precursors, which in turn produces copious amounts of metal halide waste, is the key limitation of the classical organometallic reactions. Inspired by the classical Wolff-Kishner reduction converting carbonyl groups in aldehydes or ketones into methylene derivatives, our group has recently developed strategies to couple various alcohols, aldehydes, and ketones with a broad range of both hard and soft carbon electrophiles in the presence of catalytic amounts of transition metals, via the hydrazone derivatives: i.e., as organometallic reagent surrogates. This Tutorial Review describes the chronological development of this concept in our research group, detailing its creation in the context of a deoxygenation reaction and evolution to a more general carbon-carbon bond-forming strategy. The latter is demonstrated by the employment of carbonyl-derived alkyl carbanions in various transition-metal catalyzed chemical transformations, including 1,2-carbonyl/imine addition, conjugate addition, carboxylation, olefination, cross-coupling, allylation, alkylation and hydroalkylation.

Catalytic Generation of Carbanions through Carbonyl Umpolung

Carbonyl Umpolung is a powerful strategy in organic chemistry to construct complex molecules. Over the last few years, versatile catalytic approaches for the generation of acyl anion equivalents from carbonyl compounds have been developed, but methods to obtain alkyl carbanions from carbonyl compounds in a catalytic fashion are still at an early stage. This Minireview summarizes recent progress in the generation of alkyl carbanions through catalytic carbonyl Umpolung. Two different catalytic approaches can be utilized to enable the generation of alkyl carbanions from carbonyl compounds: the catalytic Wolff–Kishner reaction and the catalytic single‐electron reduction of carbonyl compounds and imines. We discuss the reaction scope, mechanistic insights, and synthetic applications of the methods as well as potential future developments.

Oxidative Sulfonylation of Hydrazones Enabled by Synergistic Copper/Silver Catalysis

A copper/silver-cocatalyzed protocol for oxidative sulfonylation of hydrazones is demonstrated. A wide range of β-ketosulfones and N-acylsulfonamides are directly synthesized in moderate to good yields. Our work provides a viable method for scalable preparation of β-ketosulfone derivatives that have found wide applications in the pharmaceutical industry.

Empowering alcohols as carbonyl surrogates for Grignard-type reactions

The Grignard reaction is a fundamental tool for constructing C-C bonds. Although it is widely used in synthetic chemistry, it is normally applied in early stage functionalizations owing to poor functional group tolerance and less availability of carbonyls at late stages of molecular modifications. Herein, we report a Grignard-type reaction with alcohols as carbonyl surrogates by using a ruthenium(II) PNP-pincer complex as catalyst. This transformation proceeds via a carbonyl intermediate generated in situ from the dehydrogenation of alcohols, which is followed by a Grignard-type reaction with a hydrazone carbanion to form a C-C bond. The reaction conditions are mild and can tolerate a broad range of substrates. Moreover, no oxidant is involved during the entire transformation, with only H₂ and N₂ being generated as byproducts. This reaction opens up a new avenue for Grignard-type reactions by enabling the use of naturally abundant alcohols as starting materials without the need for pre-synthesizing carbonyls.

Alcohols are more naturally abundant than carbonyl compounds, which in turn are well known for their reactivity in Grignard reactions. Here, the authors showcase a distinct Grignard-like reactivity by using alcohols as coupling partners with hydrazones and synthesize more complex alcohols under ruthenium catalysis.

Palladium-catalyzed hydroalkylation of methylenecyclopropanes with simple hydrazones

A palladium-catalyzed hydroalkylation reaction of methylenecyclopropanes via highly selective C–C σ-bond scission was achieved under mild conditions, in which simple hydrazones served as carbanion equivalents. This method featured good functional group compatibility, affording high yields of C-alkylated terminal alkenes.

A palladium-catalyzed hydroalkylation of methylenecyclopropanes via selective C–C σ-bond scission was achieved, in which simple hydrazones served as carbanion equivalents. This method affords high yields of C-alkylated terminal alkenes with good functional group compatibility.