Aryl cyclopropanes

TABLE 3. Structural parameters of vinylcyclopropane (37) and trans-1,2-di vinylcyclopropane (38)  

FIGURE 7. Sections of the dynamic filtered deformation electron-density distribution of vinylcyclopropane (37). (a) The Cl—C4=C5 plane, (b) and (c) the plane normal to and through the midpoint of (b) the C1 C4 bond, and (c) the C4 C5 bond. Contours are at 0.05 e A 3 intervals, dashed lines represent negative areas. Reproduced by permission of the International Union of Crystallography from Reference 23b 

The chloro derivative 39, which has been studied by ED and molecular mechanics (MM) calculations82, exhibits the perpendicular conformation. The torsional angle is 91(3)° from ED the barrier to rotation at the ap position is 21(16) kJmol1. Structural data were obtained with large uncertainties the mean ring bond length is 1.518 (11) A. 

The double bond is longer than in ethene, 1.313 A from XD84, and rg 1.337 (2) A from ED85, and in 37, and the C—C(=) single bonds are also longer than in 37 (Table 3). The cyclopropyl groups are rotated by 66.5° from the syn bisected form, which would be 

FIGURE 8. Tetrakis(l-methylcyclopropyl)-ethene (40) molecule viewed along an axis of approximate two-fold symmetry. Drawn after Reference 83 

The double bond is longer than in ethene. 1.313 A from XD and Tj 

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A more interesting example is the aryl-cyclopropane 47. Removing the carbene we must put back the HC1 lost in the a-elimination to reveal 48. An example is with the benzylic chloride 49 that gives the bicyclic compound 47 in good yield and with high diastereoselectivity (10 1) in favour of the endo isomer shown. The strong and very hindered base 50 is used.11... 

The length of the bond connecting the cyclopropyl group and the Ph substituent can be compared with a mean of 1.490 (15) A over a sample of = 90 observations (sample standard deviation in parentheses) for aryl cyclopropanes ... 

With respect to the arylcarbenes, however, the carbene addition is not stereospecific the aryl-cyclopropanes are generally formed as mixtures of diastereomers. In almost all cases reported, the sj -isomer predominates, and this is the case even when the corresponding uw/z-isomer is far less sterically crowded. Thus, when 1-naphthylcarbene reacted with cyclopentene, the corresponding cyclopropane 6-(l-naphthyl)bicyclo[3.1.0]hexane (4) was obtained in 62% yield with endojexo ratio of 84 16. ... 

A marked solvent effect has been noted in the Lewis-acid-catalysed ring-opening of aryl cyclopropanes. Rearrangement of (404) with stannic chloride proceeds by two routes from the intermediate (405), giving a 90% combined yield of (406) and (407). The ratio of these products was 20 80 when benzene was used as solvent, but 80 20... 

In 2013, Babu et al. [39] and Charette et al. [40] disclosed the direct arylation of cyclopropanes employing the aminoquinolamide and picolinamide auxiliaries, respectively. Thus, the Babu group showed that the methylene C-H bond of cyclopropyl substrate 63 can be functionalized with excess aryl iodide in the presence of catalytic Pd(OAc)2 and stoichiometric AgOAc (Scheme 17) [39]. 2-Methylthioanilide 67 could also be employed as auxiliary however the arylated cyclopropanes 68 and 69 were obtained in lower yields. Monoarylated cyclopropanes 64-66 and 68-69 were obtained as the cis-diastereomer moreover, cis-diarylated cyclopropanes can be obtained when excess (8 equiv.) aryl iodide is employed. It is also possible to access mixed triarylated cyclopropylcarboxamides... 

SCHEME 10.39 Reaction of aryl cyclopropanes with aldehydes. 

TABLE 10.12 Reaction of Aryl Cyclopropanes with Aldehydes... 

Recently, extensive efforts have been devoted to the synthesis of cycHc peroxides since the discovery of artemisinin and related antimalarial l,2,4-trioxanes. > As described previously, PET oxygenation is a unique but effective method for the preparion of cycHc peroxides, which is also appHcable to the synthesis of the peroxide structures from arylated cyclopropanes, aziridines, and olefins. - ... 

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