Organic chemists have always been fascinated by the cyclopropane subunit.1 The smallest cycloalkane is found as a basic structural element in a wide range of naturally occurring compounds.2 Moreover, many cyclopropane-containing unnatural products have been prepared to test the bonding features of this class of highly strained cycloalkanes3 and to study enzyme mechanism or inhibition.4 Cyclopropanes have also been used as versatile synthetic intermediates in the synthesis of more functionalized cycloalkanes5,6 and acyclic compounds.7 In recent years, most of the synthetic efforts have focused on the enantioselective synthesis of cyclopropanes.8 This has remained a challenge ever since it was found that the members of the pyrethroid class of compounds were effective insecticides.9 New and more efficient methods for the preparation of these entities in enantiomerically pure form are still evolving, and this review will focus mainly on the new methods that have appeared in the literature since 1989. It will elaborate on only three types of stereoselective cyclopropanation reactions from olefins: the halomethylmetal-mediated cyclopropanation reactions (eq 1), the transition metal-catalyzed decomposition of diazo compounds (eq 2), and the nucleophilic addition-ring closure sequence (eqs 3 and 4). These three processes will be examined in the context of diastereoand enantiocontrol. In the last section of the review, other methods commonly used to make chiral, nonracemic cyclopropanes will be briefly outlined.

Stereoselective Cyclopropanation Reactions

From 2000 to mid-2010: a fruitful decade for the synthesis of pyrazoles.

Beijing National Laboratory of Molecular Sciences (BNLMS) and Key Laboratory of Bioorganic Chemistry and Molecular Engineering of Ministry of Education, College of Chemistry and Green Chemistry Center, Peking University, 202 Chengfu Road, 098#, Beijing 100871, China State Key Laboratory of Organometallic Chemistry, Chinese Academy of Sciences, 345 Lingling Road, Shanghai 200032, China State Key Laboratory of Elemento-Organic Chemistry, Nankai University, Tianjin 200060, China

Transition-Metal-Free Coupling Reactions

Recent studies on the reactions of α-diazocarbonyl compounds

Catalytic Asymmetric Synthesis of α-Amino Acids

A convenient one-pot procedure for the preparation of pyrazoles by 1,3-dipolar cycloaddition of diazo compounds generated in situ has been developed. Diazo compounds derived from aldehydes were reacted with terminal alkynes to furnish regioselectively 3,5-disubstituted pyrazoles. Furthermore, the reaction of N-vinylimidazole and diazo compounds derived from aldehydes gave exclusively 3-substituted pyrazoles in a one-pot process.

A novel one-pot method for the preparation of pyrazoles by 1,3-dipolar cycloadditions of diazo compounds generated in situ.

Catalytic cyclopropanation of alkenes using diazo compounds generated in situ. A novel route to 2-arylcyclopropylamines.

A simple and high-yielding method for the preparation of cyclopropane amino acids is described. The novel method involves the one-pot cyclopropanation of readily available dehydroamino acids using ...

Diastereoselective synthesis of cyclopropane amino acids using diazo compounds generated in situ.

A simple, user-friendly process for the homologation of aldehydes using tosylhydrazone salts

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Roger V. Bonnert

Papers

A novel one-pot method for the preparation of pyrazoles by 1,3-dipolar cycloadditions of diazo compounds generated in situ.

Catalytic cyclopropanation of alkenes using diazo compounds generated in situ. A novel route to 2-arylcyclopropylamines.

Diastereoselective synthesis of cyclopropane amino acids using diazo compounds generated in situ.

A simple, user-friendly process for the homologation of aldehydes using tosylhydrazone salts

A Novel One‐Pot Method for the Preparation of Pyrazoles by 1,3‐Dipolar Cycloadditions of Diazo Compounds Generated in situ.