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

Asymmetric 1,3-Dipolar Cycloaddition Reactions

1,1‘-Binaphthyl Dimers, Oligomers, and Polymers: Molecular Recognition, Asymmetric Catalysis, and New Materials†

2.1.8. Michael Reaction 2245 2.1.9. Others 2247 2.2. Cyclization Reactions 2248 2.2.1. Carbon Diels−Alder Reactions 2248 2.2.2. Aza-Diels−Alder Reactions 2252 2.2.3. Other Hetero-Diels−Alder Reactions 2255 2.2.4. Ionic Diels−Alder Reaction 2256 2.2.5. 1,3-Dipolar Cycloadditions 2256 2.2.6. Other Cycloaddition Reactions 2258 2.2.7. Prins-type Cyclization 2259 2.3. Friedel−Crafts Acylation and Alkylation 2259 2.4. Baylis−Hillman Reaction 2263 2.5. Radical Addition 2264 2.6. Heterocycle Synthesis 2267 2.7. Diazocarbonyl Insertion 2270 3. C−X (X ) N, O, P, Etc.) Bond Formation 2271 3.1. Aromatic Nitration and Sulfonylation 2271 3.2. Michael Reaction 2272 3.3. Glycosylation 2273 3.4. Aziridination 2275 3.5. Diazocarbonyl Insertion 2276 3.6. Ring-Opening Reactions 2277 3.7. Other C−X Bond Formations 2280 4. Oxidation and Reduction 2280 4.1. Oxidation 2280 4.2. Reduction 2281 5. Rearrangement 2283 6. Protection and Deprotection 2285 6.1. Protection 2285 6.2. Deprotection 2288 7. Polymerization 2291 8. Miscellaneous Reactions 2291 9. Lanthanide(II) Triflates in Organic Synthesis 2295 10. Conclusion 2295 11. Acknowledgment 2295 12. References 2295

Rare-earth metal triflates in organic synthesis

It was in 1963 that Huisgen laid out the classification of 1,3-dipoles and the concepts for 1,3-dipolar cycloaddition reactions, although it was not until 1976 that the first intramolecular 1,3-dipolar cycloaddition reaction of an azomethine ylide was reported. Since then, impressive developments have been described in this area, with the establishment of various useful methods for the formation of azomethine ylides and the determination of the requirements for a successful intramolecular cycloaddition reaction. Use of this methodology for the synthesis of pyrrolidineand pyrrole-containing natural products has been expanding rapidly. This review aims to describe the background and mechanisms of azomethine ylide formation and intramolecular cycloaddition, giving a critical account including the very first example and covering to early 2005. It is hoped that this review will be a useful resource for chemists interested in cycloaddition reactions and will inspire further exciting developments in this area. Cycloaddition reactions are one of the most important class of reactions in synthetic chemistry. Within * Corresponding author. Tel: +44 (0)114 222 9428. Fax: +44 (0)114 222 9346. E-mail: i.coldham@sheffield.ac.uk. † University of Sheffield. ‡ Tripos Discovery Research Ltd. Iain Coldham (b. 1965) is a Reader in Organic Chemistry at the University of Sheffield. He obtained his undergraduate degree and Ph.D. from the University of Cambridge, completing his Ph.D. in 1989 under the supervision of Stuart Warren. After postdoctoral studies at the University of Texas with Philip Magnus, he joined the staff in 1991 at the University of Exeter, U.K. In 2003, he moved to the University of Sheffield where he is involved in research on chiral organolithium compounds and on dipolar cycloaddition reactions in synthetic organic chemistry.

Intramolecular dipolar cycloaddition reactions of azomethine ylides.

Robert Naasz, Leggy A. Arnold, Mauro Pineschi,Erik Keller, and Ben L. Feringa*Department of Organic and Molecular Inorganic ChemistryUniversity of Groningen, Nijenborgh 49747 AG Groningen, The NetherlandsReceived October 23, 1998The construction of carbocyclic compounds by the Robinsonannulation is one of the essential methodologies in organic syn-thesis.

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Catalytic enantioselective annulations via 1,4-addition-aldol cyclization of functionalized organozinc reagents

The copper(II) catalyzed enantioselective 1,4-addition reactions of diethylzinc to cyclic enones in the presence of novel phosphorus amidite ligands, easily prepared from α,α,α′,α′-tetraphenyl-2,2′-dimethyl-1,3-dioxolane-4,5-dimethanol (TADDOL) derivatives, resulted in e.e.s up to 71% for cyclohexenone and up to 62% for cyclopentenone. A remarkable enhancement of enantioselectivity was observed upon the addition of powdered molecular sieves to the reaction mixture.

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Unexpected enhancement of enantioselectivity in copper(II) catalyzed conjugate addition of diethylzinc to cyclic enones with novel TADDOL phosphorus amidite ligands

Ytterbium triflate catalyzed Michael additions of β-ketoesters in water

Various diazo compounds, nitrile oxides, nitrones and azomethine ylides were examined in 1,3-dipolar cycloadditions to enantiomerically pure 5-(R)-menthyloxy-2(5H)-furanone 1a. Pyrazoline 9 was obtained in 100% c.y. as a mixture of 2 diastereoisomers in ratios up to 72 : 28, whereas pyrazoline 16 was obtained in 100 % c.y. as a single enantiomer. Photochemically pyrazolines 9 and 10 have been converted to cyclopropanes 11 and 13. Under thermal conditions pyrazoline 9 is converted to 4-methyl-5-menthyloxy-2(5H)-furanone. Isoxazoles 21a-24a were obtained enantiomerically pure via nitrile oxide addition to 1a in 64-67% yield. Nitrone addition afforded isoxazolidines 27, 28 and 34 with complete anti-facial- and regiochemistry, but with endo-exo selectivities up to 76%. Enantiomerically pure isoxazolidines were obtained in 25-75% yield. Pyrrolidine 36 was obtained diastereomerically pure in 81% c.y. Pyrrolidines 42 and 45, however, were obtained as diastereomeric mixtures in 37% resp. 6% yield.

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Asymmetric 1,3-dipolar cycloadditions to 5-(R)-menthyloxy-2(5H)-furanone

Enantioselective Michael additions of α-nitroesters 2a-d with α,β-unsaturated ketones were carried out in the presence of a catalytic amount of chiral Al-Li-(R,R′)-2,2′-dihydroxy-1,1′-binaphthyl (‘AlLiBINOL’) complex prepared in situ from LiAlH 4 and 2.45 equiv. of (R,R′)-BINOL. The enantioselectivity of the Michael addition proved to be extremely temperature dependent: Michael adduct 4a showed 7% e.e when the reaction was performed at RT, whereas 72% e.e. of the opposite enantiomer of 4a was found when the 1,4-addition was performed at −23°C. Solvent variation showed that tetrahydrofuran gave the highest selectivity (up to 80% e.e.), whereas the highest enantioselectivity for the opposite enantiomer was found in methylene chloride (up to 25%). X-Ray structure analysis of the AlLi 3 BINOL 3 complex 6 in combination with 27 Al NMR studies showed that ‘AlLiBINOL’ is a mixture of aluminium complexes in solution.

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Erik Keller

Papers

Catalytic enantioselective annulations via 1,4-addition-aldol cyclization of functionalized organozinc reagents

Unexpected enhancement of enantioselectivity in copper(II) catalyzed conjugate addition of diethylzinc to cyclic enones with novel TADDOL phosphorus amidite ligands

Ytterbium triflate catalyzed Michael additions of β-ketoesters in water

Asymmetric 1,3-dipolar cycloadditions to 5-(R)-menthyloxy-2(5H)-furanone

Catalytic enantioselective Michael addition reactions of α-nitroesters to α,β-unsaturated ketones