Of cyclopropane derivatives

The growing importance of cyclopropane derivatives (A. de Meijere, 1979), as synthetic intermediates originates in the unique, olefin-like properties of this carbocycle. Cyclopropane derivatives with one or two activating groups are easily opened (see. p. 69f.). Some of these reactions are highly regio- and stereoselective (E. Wenkert, 1970 A, B E. J. Corey, 1956 A, B, 1975 see p. 70). Many appropriately substituted cyclopropane derivatives yield 1,4-difunctional compounds under mild nucleophilic or reductive reaction conditions. Such compounds are especially useful in syntheses of cyclopentenone derivatives and of heterocycles (see also sections 1.13.3 and 4.6.4). 

In other cases, sulfenic acid elimination can involve y-hydrogen atoms with the formation of cyclopropane derivatives. y-Klimination is favored when DMSO is the reaction solvent. An example involving l-methylsulfinyl-2-ethyl-3-phenyl propane [14198-15-3] is shown in equation 13 (45) ... 

While these rearrangements are used most often to prepare large rings, it should be noted that the expansion of cyclopropane derivatives to azetidines is also practical (Scheme 6 Section 5.09.3.3.3.a). 

The preparation of cyclopropane derivatives has been greatly facilitated by the development of carbene-type intermediates (see Chapter 13) and their ready reaction with olefins. The preparation of phenylcyclopropane from styrene and the methylene iodide-zinc reagent proceeds in only modest yield, however, and the classical preparation of cyclopropane derivatives by the decomposition of pyrazolines (first employed by Buchner in 1890) is therefore presented in the procedure as a convenient alternative. 

During preparation of cyclopropane derivatives, it is important to add the diiodomethane slowly to a solution of diethylzinc in the alkene. Addition of diethylzinc to an alkene-diiodomethane mixture may be explosively violent. 

A variety of cyclopropane derivatives has been prepared by generating dichlorocarbene in the presence of alknenes. 

The photoelimination of nitrogen from 1-pyrazolines is one of the most thoroughly investigated photoreactions and it has been used extensively in the synthesis of cyclopropane derivatives.334 Both stereospecific and non-stereospedfic processes have been observed and these are believed, at least in simple 1-pyrazolines, to correspond to singlet and triplet excited states, respectively. Two reaction pathways have been proposed in the azoalkane 405335 direct excitation via a thermally activated S, state affords the C6H6 isomers 406 to 409, whereas triplet-sensitized excitation results in a tem-... 

However, the generation of cyclopropane derivatives was also shown to implicate an alternate route not requiring a metallocyclobutane transition state (14). In addition, a metathesis catalyst successfully converted certain cyclopropanes to metathesis-related olefins by way of a carbene elimination process (15-17), according to Eq. (3). 

His research interests deal with the chemistry of cyclopropane derivatives, 1,3-dipolar cycloadditions, synthesis of natural compounds and biologically active analogues. Recently, the research activity is also dedicated to synthetic studies for the production of new materials light-harvesting antenna systems and functionalized organogelators. 

Scheme 77. Synthetic sequence to obtain a combinatorial library of cyclopropane derivatives ...

Table 1. Electron Transfer Induced Reactions of Cyclopropane Derivatives... 

Sulfur ylides are among the most interesting carbon nucleophiles and their synthetic importance has been recently reviewed.One especially interesting use of these ylides is their application to the synthesis of cyclopropane derivatives using unsaturated oxazolones. For example, stabilized sulfur yhdes react with unsaturated oxazolones 629 via a Michael reaction to give oxazolone spirocyclopropanes 630 as shown in Scheme 7.202 and Table 7.46 (Fig. 7.57), whereas the less stabilized sulfur ylides give ring-opened products 631 as the major compounds (Scheme 7.202). ... 

Since (Z)- and ( )-stereoisomers of unsaturated oxazolones can be obtained using appropriate isomerization procedures, cis and trans isomers of cyclopropane derivatives can be obtained in a stereoselective manner, although special care must be taken with experimental conditions to obtain the best stereoselectivity. Both racemic cis- and fraui-l-amino-2-phenylcyclopropanecarboxylic acid 641 and 644 have been obtained from the corresponding (Z)- or ( )-4-benzylidene-2-phenyl-5(4//)-oxazolone 621 and 642 using diazomethane. Care was taken to affect the... 

A large number of cyclopropanated derivatives of Cgo in which the bridging atom is an electron rich transition metal (see Fig. 16) such as Pt, Pd, Ni, Ir, W, Mo, and Rh has been reported. Their electrochemical properties have been reviewed [83, 141, 142] and, in general, reductions are Cgo centered and negatively shifted with respect to those of pure Cgo, while oxidations are metal centered. In most cases, however, the first reduction is accompanied by breakage of the carbon-metal bonds and recovery of the pristine [60] fullerene. In multiadduct derivatives, the breakage occurs in a stepwise manner. 

Scheme 29 Formation of cyclopropane derivatives catalyzed by RCIg.

Starting from optically active 1-chlorovinyl p-tolyl sulfoxide derived from 2-cyclohex-enone, the asymmetric synthesis of cyclopropane derivative (85) was realized (equation 23) . Addition reaction of lithium enolate of tert-butyl acetate to 83 gave the adduct (84) in 96% yield with over 99% ee. Treatment of the latter with i-PrMgCl in a similar way as described above afforded optically pure (15,6/ )-bicyclo[4.1.0]hept-2-ene (85) in 90% yield. 

Since then, not only has the scope of the reaction been widely studied, but also structural variations of the reagents and the reaction conditions in order to further increase its synthetic utility. The following sections will present the latest, state-of-the-art methodologies for the generation of cyclopropane derivatives using zinc carbenoid reagents. 

This method is generally applicable to the stereospecific synthesis of cyclopropane derivatives from a large variety of substituted olefins.4... 

Particularly interesting applications of isopropylidenediphenylsulfuran [459, 464] have been reported. Improvements in its preparation and use led [465] to a claimed industrially viable stereoselective synthesis of Deltamethrin, the most potent commercially available insecticide, as well as to other stereoselective syntheses of cyclopropane derivatives [466]. 

About a hundred new structures containing a three-membered carbocyclic ring are added to the CSD in a year. The wealth and diversity of the relevant material render a thorough and systematic treatment of all classes of cyclopropane derivatives impossible. I have selected mainly simple molecules and systems of some structural interest, and have resorted to earlier studies in some cases in order to include some basic molecules. Fused... 

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