Carbenes INDEX

S CONTENTS Introduction to the Series An Editor s Foreword, Albert Padwa. Preface, Dennis P. Curran. Intramolecular 1,3-Dipolar Cycloaddition Chemistry, Albert Padwa and Allen M. Schoffstall. Stereochemical and Synthetic Studies of the Intramolecular Diels-Alder Reaction, William R. Roush. Thermal Reaction of Cyclopropenone Ketals, Key Mechanistic Features, Scope and Application of the Cycloaddition Reactions of Cyclopropenone Ketals and p - Delocalized Singlet Vinyl Carbenes Three Carbon 1,1-/1,3-Dipoles, Dale L. Boger and Christine E. Brotherton-Pleiss. Index. 

Current IUPAC and Chemical Abstracts nomenclature has been employed in this index with the former given preference. Substitutive nomenclature has been given preference over radicofunc-tional, additive, subtractive, conjunctive or replacement nomenclature, except where this becomes unwieldy. With many bicyclic and polycyclic compounds bearing heteroatoms, standard bicyclic or polycyclic oxa, aza, and thia replacement nomenclature has often been used. With certain functional groups, where the names are rather complex and probably not familiar to most organic chemists, such as ylides, those compounds have simply been named as sulfur, tellurium and arsonic ylides. Metal carbenes have been treated similarly. With more complex functionality and many heterocycles, the Beilstein Commander Crossfire nomenclature system has been used with certain modifications. 

The correlation between the carbcnc selectivity and its substitution has been disclosed In Moss s classical work (ll- He defined a selectivity index mexY of a carbene as the slope of the linear correlations obtained by plotting [log(fc/Ao)] c fK versus [log(/fMo)lcc/2 corresponds to the cyclo-... 

The relative reactivity of alkenes toward various carbenes and carbenoids has been compiled Recently, a selectivity index, mcxv which can be estimated from the dual... 

The electrophilicity index also accounts for the electrophilic activation/deactivation effects promoted by EW and electron-releasing substituents even beyond the case of cycloaddition processes. These effects are assessed as responses at the active site of the molecules. The empirical Hammett-like relationships found between the global and local electrophilicity indexes and the reaction rate coefficients correctly account for the substrate selectivity in Friedel-Crafts reactions, the reactivity of carbenium ions, the hydrolysis of esters, the reactivity at the carbon-carbon double bonds in conjugated Michael additions, the philicity pattern of carbenes and the superelectrophilicity of nitronium, oxonium and carboxonium ions. This last application is a very promising area of application. The enhanced electrophilicity pattern in these series results from... 

Dibromocarbene is one of the most reactive (the least selective) carbenes (Houben-Weyl, Vol. E19b, p 1598). Its selectivity index 0.65, if generated from bromoform and potassium... 

Benzyloxy(cyano)carbene would be expected to be electrophilic by virtue of the calculated selectivity index, Wp -HjOccN 111- This has not yet been experimentally proved as 3-bcnzyloxy-3-cyano-3//-diazirine is rather labile and cannot be isolated if it is synthesized by the substitution of chlorine by a cyano group in 3-benzyloxy-3-chloro-3if-diazirine consequently, this substitution reaction is carried out in the presence of an alkene, hence, preparing 1-benzyloxy-cyclopropane-l-carbonitrile derivatives. However, the cyanide ion present in the system induces the polymerization of electrophilic alkenes, such as acrylonitrile or methyl acrylate. 

See Sections 4.1, 4,2, 4,3 and 4.3.3 for definitions alternatively, look in the index for relevant page numbers. The main types of reactions of carbanions and carbenes are listed in Section 4.3.3. 

To further characterize the selectivity of carbene CXY, we can compare its discrimination between the olefins of the standard set with that of CCI2, which we designate the standard carbene. We plot the logarithms of the relative reactivities for CXY against analogous data for CCI2 (with the relative reactivities all adjusted to the standard alkene, isobutene, = 1.00), and then determine the slope of the correlation line, Wcxy- We call m xy the carbene selectivity index, defined as the least-squares slope of log (V o)cxy s. log (kJk QQX. [8,9,16,17] The m xv values for the carbenes of Table 1, determined in this manner, are m p = 1.48 mcci, 1-00 (by definition), and m Br, 0-65. 

The results with dimethoxyearbene highlight an inherent deficiency of Eq. 4 it is an empirical correlation of parameters normalized to the electrophilic car-bene, CCI2. Its electrophilic heritage means that although the equation can predict values for highly resonance stabilized, nucleophilic carbenes such as (MeO)2C or Me2NCOMe, these are virtual selectivity indexes. The nucleophilic carbenes simply do not add to the aUcenes of the standard set. However, the equation helps us define the Wcxy regions in which electrophilic and nucleophilic carbenes reside. The electrophilic species, which react appropriately with the standard alkenes of Table 1, exhibit w xy values between 0.29 (BrCCOOEt) and... 

Our empirical analysis of selectivity in the carbene/alkene cyclopropanation reaction has now furnished both a quantitative index of selectivity and examples... 

Schoeller and Brinker applied single electron perturbation theory to carbene/ alkene additions and elaborated a construct that was almost indentical to our FMO analysis. [74] Schoeller also focused on estimating LUMO(carbene)/ HOMO(alkene) and LUMO(alkene)/HOMO(carbene) differential energies, and derived a selectivity index , S, which roughly paralleled and predicted the electrophilicity of the dihalocarbenes and the nucelophilicity of (e.g.), C(NH2)2, C(0H)2, and C(SMe)2. [74]... 

Flowever, PhCOMe has m icalcd) = 1.34. According to our empirical analysis of carbenic selectivity (Section 1.2), it should be an electrophile because its WcxY selectivity index lies between 0.29 and 1.48. What s wrong FMO... 

The electrophilic, ambiphilic and nucleophilic characters of a range of singlet carbenes have been compared to their intrinsic reactivity index This quantification is supposed to evaluate the nucleophilic and electrophilic properties of compounds and has been previously assessed for a range of organic compounds but appears unadapted to singlet carbene and presents no advantages compared to frontier molecular orbital and empirical evaluations. 

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