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Aryl-aryl bond formation one century after the discovery of the Ullmann reaction.

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Advances in transition metal (Pd, Ni, Fe)-catalyzed cross-coupling reactions using alkyl-organometallics as reaction partners.

Cyclodextrins are extremely attractive components of artificial enzymes and other biomimetic materials. They are readily available, they bind hydrophobic substrates into their cavities in water solution, and they have two rims of hydroxyl groups (Figure 1) that can either react with substrates themselves or be used to attach other catalytic and functional groups. Of course, they have disadvantages. For one, unless they are extensively modified their complexes with substrates can be rather flexible and, perhaps, with unpredictable preferred geometry. They are also unstable to strong acid. Thus for some purposes such synthetic cavity species as calixerenes1 or synthetic macrocycles2-4 may have advantages. However, one of the chief advantages of cyclodextrins is highly attractivesthey are readily available, so it is possible to avoid the synthesis of a binding group and go directly to studies of what can be achieved with their use. Afterward, the lessons learned may be applied to other systems with advantage. This review will cover all the literature on reactions in which cyclodextrins bind substrates and then either catalyze their reactions or mimic a step in an enzymatic catalytic sequence. However, it will not describe work in which cyclodextrins simply change the course of a reaction without playing an obvious catalytic role involving substrate binding. For example, there are systems in which the main function of the cyclodextrin seems to be to complex a metal ion and keep it in solution.5-11 There are other studies in which binding into a cyclodextrin simply alters the selectivity of attack by an external reagent in some way12-24 or causes solubilization to facilitate phase transfer catalysis.12,25,26 Presumably such other areas are described elsewhere in this volume. While much work on artificial enzymes using cyclodextrins has been done in the author’s laboratory, and will be described, every effort is made to describe all the relevant work in the field. Several reviews of this subject already exist and should be consulted for further information.2,27-70 The readily Ronald Breslow, born in 1931 in Rahway, NJ, completed his B.A. in chemistry in1952, his M.A. in medical science in 1953, and his Ph.D. in chemistry in 1955 with R. B. Woodward, all at Harvard University. After a postdoctoral year with Alexander Todd in Cambridge, he came to Columbia University where he is now University Professor and Professor of Chemistry. His work on enzyme models, on novel conjugated aromatic and antiaromatic molecules, on electrochemical and hydrophobic methods in mechanistic chemistry, and on anticancer cytodifferentiating agents has been recognized by a number of awards, including the U.S. National Medal of Science. In 1996, he served as President of the American Chemical Society.

Biomimetic Reactions Catalyzed by Cyclodextrins and Their Derivatives.

Mixtures of palladium acetate and o-(di-tert-butylphosphino)biphenyl (4) catalyze the room-temperature Suzuki coupling of aryl bromides and aryl chlorides with 0.5−1.0 mol % Pd. Use of o-(dicyclohexylphosphino)biphenyl (2) allows Suzuki couplings to be carried out at low catalyst loadings (0.000001−0.02 mol % Pd). The process tolerates a broad range of functional groups and substrate combinations including the use of sterically hindered substrates. This is the most active catalyst system in terms of reaction temperature, turnover number, and steric tolerance which has been reported to date.

Highly Active Palladium Catalysts for Suzuki Coupling Reactions

Organomagnesium reagents occupy a central position in synthetic organic and organometallic chemistry. Recently, the halogen-magnesium exchange has considerably extended the range of functionalized Grignard reagents available for synthetic purposes. Functional groups such as esters, nitriles, iodides, imines, or even nitro groups can be present in a wide range of aromatic and heterocyclic organomagnesium reagents. Also various highly functionalized alkenyl magnesium species can be prepared. These recent developments as well as new applications of organomagnesium reagents in cross-coupling reactions and amination reactions will be covered in this Review.

Highly functionalized organomagnesium reagents prepared through halogen-metal exchange.

Preparation of highly functionalized magnesium, zinc, and copper aryl and alkenyl organometallics via the corresponding organolithiums

A new preparation of highly functionaized aromatic and heteroaromatic zinc and copper organometallics

Preparation of polyfunctional aryl and alkenyl zinc halides from functionalized unsaturated organolithiums and their reactivity in cross-coupling and conjugated addition reactions

Synthesis and reactivity of open-chain and cyclic 2-cyano zinc and copper organometallics

Polyfunctional and stereochemically pure (E) or (Z) alkenylcopper reagents have been generated by carbocupration of terminal alkynes or by an iodine–lithium exchange reaction and have been found to add to various diethyl alkylidenemalonates, affording γ,δ-unsaturated esters in excellent yields.

Tahir N. Majid

Papers

Preparation of highly functionalized magnesium, zinc, and copper aryl and alkenyl organometallics via the corresponding organolithiums

A new preparation of highly functionaized aromatic and heteroaromatic zinc and copper organometallics

Preparation of polyfunctional aryl and alkenyl zinc halides from functionalized unsaturated organolithiums and their reactivity in cross-coupling and conjugated addition reactions

Synthesis and reactivity of open-chain and cyclic 2-cyano zinc and copper organometallics

Addition of polyfunctional and pure (E or Z) alkenylcopper and arylcopper compounds to alkylidenemalonates