In the investigation of efficient chemical transformations, the carbon-carbon bond-forming reactions play an outstanding role. In this context, organocatalytic processes have achieved considerable attention. 1 Beside their facile reaction course, selectivity, and environmental friendliness, new synthetic strategies are made possible. Particularly, the inversion of the classical reactivity (Umpolung) opens up new synthetic pathways. 2 In nature, the coenzyme thiamine (vitamin B1), a natural thiazolium salt, utilizes a catalytic variant of this concept in biochemical processes as nucleophilic acylations. 3 The catalytically active species is a nucleophilic carbene. 4

Organocatalysis by N-Heterocyclic Carbenes

Asymmetric enamine catalysis.

Small-molecule H-bond donors in asymmetric catalysis.

4.2.8. Reductive Coupling 3109 5. Reaction of Aromatic Compounds 3110 5.1. Electrophilic Substitutions 3110 5.2. Radical Substitution 3111 5.3. Oxidative Coupling 3111 5.4. Photochemical Reactions 3111 6. Reaction of Carbonyl Compounds 3111 6.1. Nucleophilic Additions 3111 6.1.1. Allylation 3111 6.1.2. Propargylation 3120 6.1.3. Benzylation 3121 6.1.4. Arylation/Vinylation 3121 6.1.5. Alkynylation 3121 6.1.6. Alkylation 3121 6.1.7. Reformatsky-Type Reaction 3122 6.1.8. Direct Aldol Reaction 3122 6.1.9. Mukaiyama Aldol Reaction 3124 6.1.10. Hydrogen Cyanide Addition 3125 6.2. Pinacol Coupling 3126 6.3. Wittig Reactions 3126 7. Reaction of R,â-Unsaturated Carbonyl Compounds 3127

Organic Reactions in Aqueous Media with a Focus on Carbon−Carbon Bond Formations: A Decade Update

Over the past decade, the most significant, conceptual advances in the field of fluorination were enabled most prominently by organo- and transition-metal catalysis. The most challenging transformation remains the formation of the parent C-F bond, primarily as a consequence of the high hydration energy of fluoride, strong metal-fluorine bonds, and highly polarized bonds to fluorine. Most fluorination reactions still lack generality, predictability, and cost-efficiency. Despite all current limitations, modern fluorination methods have made fluorinated molecules more readily available than ever before and have begun to have an impact on research areas that do not require large amounts of material, such as drug discovery and positron emission tomography. This Review gives a brief summary of conventional fluorination reactions, including those reactions that introduce fluorinated functional groups, and focuses on modern developments in the field.

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Introduction of Fluorine and Fluorine-Containing Functional Groups

Insertion of one methylene unit into the C-C bond of cyclohexanones is a potentially useful, straightforward method for the construction of seven-membered carbocycles. An especially appealing but largely unexplored method in this arena is the nucleophilic addition of diazoalkanes to the Lewis acid-activated cyclohexanones and subsequent ring expansion accompanied by the extrusion of nitrogen (direct Tiffeneau-Demjanov-type ring expansion). Our primary finding is the unprecedented insertion of alpha-alkyldiazoacetates to cyclohexanone and its heteroanalogues, generating seven-membered rings with one all-carbon quaternary center. On the basis of this finding, highly diastereoselective ring expansion of substituted cyclohexanones was developed, furnishing seven-membered rings with 1,4-quaternary-tertiary, 1,4-quaternary-quaternary, or 1,3,5-quaternary-tertiary-tertiary stereogenic centers in a single operation starting from readily available materials. The stereochemical outcome of the product can be easily predicted from the conformation of starting cyclohexanones. Enantioenriched products could be also accessed by the use of (-)-phenylmenthyl alpha-alkyldiazoacetates.

Stereoselective Construction of Seven‐Membered Rings with an All‐Carbon Quaternary Center by Direct Tiffeneau—Demjanov‐Type Ring Expansion.

A new type of fluoride ion catalyzed allylation agent, o -bis(allyldimethylsilyl)benzene ( 1a ) and bis(allyldimethylsilyl)methane ( 1b ), can be successfully utilized for various carbonyl substrates. The rate acceleration is ascribable to the shift of equilibrium to complex with Bu 4 NF by the favorable chelation of bis(silane) toward the fluoride ion.

o-Bis(allyldimethylsilyl)benzene as a Remarkably Effective Allylation Agent for Carbonyl Compounds with Bu4NF Catalyst.

Synthesis of Acyl Fluorides from Carboxylic Acids with KI/AgSCF3 for Efficient Amide and Peptide Synthesis

The hydroalumination of a terminal allene, 1,2-nonadiene, with LiAlH4 in THF using [TiCl2(Cp)2], TiCl4, TiCl3, ZrCl4, and [ZrCl2(Cp)2] catalysts afforded a wide variety of deuterated species by quenching hydroalumination products with D2O, while PhB(OH)2-catalyzed hydroalumination with AlHCl2 in ether gave >95% pure 1-nonene-3-d as predominant product (92%) in high yield. The allylation of benzaldehyde using the PhB(OH)2-catalyzed hydroalumination product suggested that the resulting hydroalumination product may be the allylaluminum compound, 2-nonenylaluminum dichloride. Allylation of trans-cinnamaldehyde using this allylaluminum compound proceeded with high regioselectivity, leaving the ketone functionality intact. Allylative ring-opening reaction of epoxides was less regioselective. The combination of catalytic PhB(OH)2 with AlHCl2 also was effective for the regioselective hydroalumination of the disubstituted allenes, vinylidenecyclohexane and 1-trimethylsilyl-1,2-nonadiene, although the trisubstitute...

Regioselective Hydroalumination of Allenes and Their Synthetic Application.

Metal‐Free C—H Bond Activation of Branched Aldehydes with a Hypervalent Iodine(III) Catalyst under Visible‐Light Photolysis: Successful Trapping with Electron‐Deficient Olefins.

Keiji Maruoka

Papers

Stereoselective Construction of Seven‐Membered Rings with an All‐Carbon Quaternary Center by Direct Tiffeneau—Demjanov‐Type Ring Expansion.

o-Bis(allyldimethylsilyl)benzene as a Remarkably Effective Allylation Agent for Carbonyl Compounds with Bu4NF Catalyst.

Synthesis of Acyl Fluorides from Carboxylic Acids with KI/AgSCF3 for Efficient Amide and Peptide Synthesis

Regioselective Hydroalumination of Allenes and Their Synthetic Application.

Metal‐Free C—H Bond Activation of Branched Aldehydes with a Hypervalent Iodine(III) Catalyst under Visible‐Light Photolysis: Successful Trapping with Electron‐Deficient Olefins.