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

Enantiomerically pure cyclobutane derivatives and their use in organic synthesis.

This review covers the recent advances in hydrosilylation chemistry mainly published in the last decade. Hydrosilylation of olefins is an important reaction for the production of various organosilicon compounds such as industrially important silicone products. Although the utility of platinum catalysts, Speier's and Karstedt's catalysts, has been widely recognized in this field for decades, development of more efficient, selective, and cheaper catalyst systems are still desired for more economical production of organosilicon materials having superior properties. In these contexts, much progress has been made in recent years. In the platinum catalysis systems, continuous progress has been made to further improve selectivity and activity. Several non-precious metal catalysts, such as Fe and Ni catalysts, with good efficiency and selectivity have been developed. Furthermore, unique chemo- and regioselectivity have been achieved not only by precious metal catalysts but also by non-precious metal catalysts. The utility of non-transition metal catalysts including early main group metals, Lewis acidic alane, borane and phosphonium salts as well as N-heterocyclic carbenes has also been disclosed.

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Hydrosilylation reaction of olefins: recent advances and perspectives

Stereoselective formation of quaternary carbon centers and related functions

Recent advances in the synthesis of piperidones and piperidines

Chiral Non-Racemic Bicyclic Lactams. Auxiliary-Based Asymmetric Reactions

Allyldimethyltritylsilane (ADTS, 1) has been employed to access a variety of cyclopentanols via Lewis acid mediated annulation to electron deficient olefins. The intermediate silylcyclopentanes were converted to their respective cyclopentanols under mild, nonepimerizing oxidative conditions. In addition, ADTS undergoes efficient annulation onto aldehydes to provide oxetanes and tetrahydrofurans. Some preliminary investigations of this annulation to chiral nonracemic bicyclic lactams are presented.

Michael D. Groaning

Papers

Chiral Non-Racemic Bicyclic Lactams. Auxiliary-Based Asymmetric Reactions

Allyldimethyltritylsilane. Synthesis of Cyclopentanols, Oxetanes, and Tetrahydrofurans by Reaction with Electron Deficient Olefins

Concise synthesis of indolizidines: total synthesis of (−)-coniceine

An asymmetric synthesis of the key precursor to (−)-indolizomycin

Allyldimethyltritylsilane: construction of enantiomerically pure cyclobutano[c]fused pyrrolidines