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

Cyclic organic carbonates represent a relevant class of chemicals that can be prepared from CO2 by cycloaddition to epoxides. The application of efficient catalysts is crucial in allowing the cycloaddition reaction to proceed under very mild conditions of temperature, pressure, and CO2 concentration, thus resulting in a sustainable and carbon-balanced approach to CO2 conversion. This is particularly the case if impure waste CO2 could be employed as a feedstock. In this Review, we have critically analyzed the burgeoning literature on the cycloaddition of CO2 to epoxides with the aim to provide state-of-the-art knowledge on the catalysts that can convert CO2 to carbonates under ambient conditions. These have been systematically organized in families of compounds and critically scrutinized in terms of catalytic activity, availability and mechanistic features. Finally, we provide an overview on the catalytic systems able to function using diluted and impure CO2 as a feedstock.

Catalytic Strategies for the Cycloaddition of Pure, Diluted, and Waste CO2 to Epoxides under Ambient Conditions

Chemical equations that balance bond types and atom hybridization to different degrees are often used in computational thermochemistry, for example, to increase accuracy when lower levels of theory are employed. We expose the widespread confusion over such classes of equations and demonstrate that the two most widely used definitions of "homodesmotic" reactions are not equivalent. New definitions are introduced, and a consistent hierarchy of reaction classes (RC1-RC5) for hydrocarbons is constructed: isogyric (RC1) superset of isodesmic (RC2) superset of hypohomodesmotic (RC3) superset of homodesmotic (RC4) superset of hyperhomodesmotic (RC5). Each of these successively conserves larger molecular fragments. The concept of isodesmic bond separation reactions is generalized to all classes in this hierarchy, providing a unique sectioning of a given molecule for each reaction type. Several ab initio and density functional methods are applied to the bond separation reactions of 38 hydrocarbons containing five or six carbon atoms. RC4 and RC5 reactions provide bond separation enthalpies with errors consistently less than 0.4 kcal mol(-1) across a wide range of theoretical levels, performing significantly better than the other reaction types and far superior to atomization routes. Our recommended bond separation reactions are demonstrated by determining the enthalpies of formation (at 298 K) of 1,3,5-hexatriyne (163.7 +/- 0.4 kcal mol(-1)), 1,3,5,7-octatetrayne (217.5 +/- 0.6 kcal mol(-1)), the larger polyynes C(10)H(2) through C(26)H(2), and an infinite acetylenic carbon chain.

/pdf/a-hierarchy-of-homodesmotic-reactions-for-thermochemistry-1gi2izjizw.pdf

A hierarchy of homodesmotic reactions for thermochemistry.

Regioselective syntheses of substituted furans

Copper-Catalyzed Diels−Alder Reactions

Synthesis of Spiro-β-Methylene-γ-Butyrolactones

Gil Valdo Jose da Silva * , Vladimir Constantino Gomes Heleno and Mauricio Gomes Consta n tinoDepartamento de Quimica, Faculdade de Filosofia, Ciencias e Letras de Ribeirao Preto, Universidade deSao Paulo, Av. Bandeirantes 3900, 14040-901 – Ribeirao Preto – SP, BrazilTel: +55/16 602 3699, Fax: +55/16 633 8151, E-mail: gvjdsilv@usp.brReceived: 18 February 2000 / Accepted: 20 June 2000 / Published: 27 June 2000Abstract: Goyazensolide, a biologically active natural product classified as a furo-heliangolide, was transformed in a phthalimide derivative that showed an enhanced biologicalactivity against Tripanosoma cruzi . The complex natural product was also reduced with highstereoselectivity by hydrogen/Wilkinson’s catalyst; an epimer of this product was obtained inthe reduction with hydrogen/Pd-C.Keywords: Furo-heliangolides, Goyazensolide, Reduction, Phthalimide derivative, Wilkin-son’s catalyst.IntroductionGoyazensolide is a natural product isolated from a Brazilian plant, Eremanthus goyazensis (Comp o-sitae, tribe Vernoniae), collected in Minas Gerais State [1,2]. It is a furo-heliangolide possessing schi s-tosomicidal and cytotoxic properties and can usually be isolated in larger amounts than many other bi o-logically active products of similar structure found on the same plant or in other plants of the same sp e-cies. Seeking methods for the preparation of the more scarce natural products or biologically active d e-rivatives from the relatively abundant goyazensolide, we have recently carried out some chemicaltransformations of this product. To this extent we have succeeded in preparing a phthalimide derivative2 with enhanced biological activity against Tripanosoma cruzi and in reducing 1 with high stereosele c-tivity by H

https://www.mdpi.com/1420-3049/5/6/908/pdf

Reduction and Preparation of a Phthalimide Derivative from a Furo-heliangolide

Synthesis of (±)-1-(2,6,6-trimethyl-4-hydroxycyclohexenyl)-1,3-butanedione (1), a marine natural product

In this paper we describe three computer programs in Basic language about the Fourier transform (FFT) which are available in the Internet site http://artemis.ffclrp.usp.br/SoftwareE.htm (in English) or http://artemis.ffclrp.usp.br/softwareP.htm (in Portuguese) since October 1998. Those are addresses to the Web Page of our Laboratory of Organic Synthesis. The programs can be downloaded and used by anyone who is interested on the subject. The texts, menus and captions in the programs are written in English.

/pdf/a-transformada-de-fourier-em-basic-28tny7ii8z.pdf

A transformada de Fourier em basic

Synthesis of Substituted γ-Butyrolactones: β-Hydroxymethyl-, β-Methylene and Cyclopropane Derivatives

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Mauricio Gomes Constantino

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