Electrophilic cyclopropanes

The similarity between the reactions of alkenes and cyclopropanes is further demonstrated by the reactions of electrophilic cyclopropanes and cyclopropenes with enamines. Cyclopropylcyanoester74, when treated with the pyrrolidine enamine of cyclohexanone, undergoes what would be a 1,2 cycloaddition in the analogous alkene case, but is actually a 1,3 cycloaddition here, to form adduct 75 (90). A similar reaction between the... 

While a large number of studies have been reported for conjugate addition and Sn2 alkylation reactions, the mechanisms of many important organocopper-promoted reactions have not been discussed. These include substitution on sp carbons, acylation with acyl halides [168], additions to carbonyl compounds, oxidative couplings [169], nucleophilic opening of electrophilic cyclopropanes [170], and the Kocienski reaction [171]. The chemistry of organocopper(II) species has rarely been studied experimentally [172-174], nor theoretically, save for some trapping experiments on the reaction of alkyl radicals with Cu(I) species in aqueous solution [175]. 

In a similar manner, A-Cbz-a-Lys-OMe reacted with an electrophilic cyclopropane derivative, and a mixture of diastereomeric y-lactams was isolated. The reaction is postulated to proceed by an attack of the amino group on the methylene group with subsequent cyclization (Scheme 4) (85JOC3631). 

Perfluoroalkyl)methyl-substituted electrophilic cyclopropanes are synthesized in excellent yields by a chromium (III) chloride/iron powder-promoted reaction of perfluoroalkyl iodides with allylamalonic ester and its analogues (equation 51)67. Oxidative coupling of... 

Metal catalysed decomposition of diazocarbonyl compounds in the presence of alkenes provides a facile and powerful means of constructing electrophilic cyclopropanes. The cyclopropanation process can proceed intermolecularly or intramolecularly. Early work on the topic of intramolecular cyclopropanation (mainly using diazoketones as precursors) has been surveyed31. With the discovery of powerful group VIII metal catalysts, in particular the rhodium(II) derivatives, metal catalysed cyclopropanation of diazocarbonyls is currently the most fertile area in cyclopropyl chemistry. In this section, we will review the efficiency and versatility of the various catalysts employed in the cyclopropanation of diazocarbonyls. Cyclopropanations have been organized according to the types of diazocarbonyl precursors. Emphasis is placed on recent examples. 

Tazuke reported the carboxylation of the radical anions of aromatic hydrocarbons that are generated by photoinduced electron- transfer from the tertiary amines to the excited singlet aromatic hydrocarbons (Scheme 36) [119]. Toki and his coworkers reported the photofixation of COj with styrene using tertiary amines as electron donors [120]. Tomioka reported the photoaddition of tertiary amines to electrophilic cyclopropanes [115]. 

From our previous discussion about electrophilic cyclopropanes (see Problem 15), it should be remembered that a marked reduction of electron density in the three-membered ring occurs when strong electron withdrawing groups are substituted either directly or in conjugation with the trimethylene ring and... 

Very often protic acids are used to cleave electrophilic cyclopropanes. Some typical examples are given in equations 44-46 " 100-102... 

B. Reaction of Electrophilic Cyclopropanes with Nucleophiles and Bases. 519... 

Reaction of electrophilic cyclopropanes with oxygen nucleophiles and bases. 519... 

Reaction of electrophilic cyclopropanes with sulphur and selenium nucleophiles 526... 

C. Electrophile-initiated Ring Transformations of Electrophilic Cyclopropanes 549... 

Although the first electrophilic cyclopropane, diethyl cyclopropane-1,1-dicarboxylate (EWG = COOEt = H), was prepared a century ago in 1885 by... 

This chapter will deal mainly with the synthesis and reactivity of electrophilic cyclopropanes and only these procedures and reactions will be investigated which give rise to cyclopropanes geminally substituted with two EWGs. Nevertheless, the preparation of monoactivated cyclopropanes will be mentioned to some extent because a number of procedures for the synthesis of electrophilic cyclopropanes have been developed for cyclopropanes bearing one EWG. Therefore, the synthesis and reactivity of the latter compounds cannot be excluded, due to the close relationship and the numerous studies concerning reaction mechanisms for these compounds. 

Also functional group transformations of electrophilic cyclopropanes yielding other electrophilic cyclopropanes will not be the subject of this chapter. 

This review covers the literature on electrophilic cyclopropanes up to the end of 1984. 

In this chapter the general methods leading to these electrophilic cyclopropanes will be described and the procedures are classified according to the reaction type and not to the substrates and/or reagents. Some mechanistic interpretations of the results will be treated in some important cases. 

The electrophilic cyclopropane 59 is prepared according to a reaction scheme which involved the photolysis of ethyl diazoethylidenecyanoacetate (56) to give the cyclopropene (57) derivative which in turn on addition of diphenyldiazomethane afforded the bicyclic pyrazoline (58). Thermolysis of 58 produced bicyclo[ 1.1.0]butane derivative 59 (equation 9). ... 

Chiral electrophilic cyclopropanes (63) are prepared in high enantiomeric excess starting from butadiene-iron tricarbonyl complexes (60) containing a non-complexed double bond. Reaction with diazomethane and decomposition of the resulting pyrazolines (61) in the presence of Ce" gave the corresponding chiral cyclopropanes (62). Breakdown of the dienic substituent of electrophilic cyclopropane (62) by means of ozonization resulted in the formation of formyl-substituted electrophilic cyclopropane (63) still carrying the asymmetric centre (equation 10) " . ... 

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