Electronic effects cyclopropyl groups

The products obtained in the reaction of A -cyclopropyl-4,5-difluoroanthranilic acid hydrazides 429 with triphosgene were dependent on the steric hindrance imposed by substituent R at position 3, and not the electronic effect of this group. While the unsubstituted compound 429 (R = H) gave exclusively the 4-hydrazono-3,l-benzoxazin-2-one-type product 430, the similar reactions of the chloro-, methyl-, and methoxy-substituted analogs 429 (R = Cl, Me, OMe) resulted in formation of the corresponding quinazoline-2,4-diones 431 as the sole products. For the fluoro-substituted compound 429 (R = F), a 20 80 mixture of the products 430 and 431 was obtained (Equation 46) <2005JHC669>. 

In consideration of these results" de Meijere concluded" the cyclopropyl group has an inductive electron-attracting effect in this case and destabilizes the intermediate carbenium ion . However, the destabilization referred to is for spiro cyclopropyl relative to a tert-butyl... 

The relative rates of dichlorocarbene addition to cyclopropylalkenes showed some significant differences (Table 23) that were attributed to the combined influence of steric and electronic factors It was concluded that unique effects due to the cyclopropyl groups did not occur in this concerted cycloaddition. ... 

This latter assumption is not necessary when the reaction is analyzed by ESR spectroscopy since one is observing the radical directly. Table 13 lists the structures of the thermodynamically (ESR) or chemically more favored cyclopropyl radicals. There are a number of factors which will influence the position of the equilibrium. Among them are steric effects and electronic effects. As can be seen in Table 13, entries 5, 6 and 13-21 are examples in which the position of the equilibrium is influenced by steric interactions. Entry 5 shows that the (t orbital containing the odd electron prefers to be cis to the phenyl group... 

The cyclopropane chemical reactivity, which closely resembles that of an olefinic double bond, stems from the electronic properties of this three-membered carbocycle Effectively, cyclopropyl and olefinic groups interact with neighbouring 7c-electron systems and p-electron centres they both add acids, halogens and ozone, undergo catalytic hydrogenation and cycloaddition, form metal complexes, etc. 

The cyclopropyl rest is less bulky than the isopropyl group for a maximal electron-donor effect. This electroiuc effect is involved when the cyclopropyl group of efavirenz, a nonnucleoside reverse transcriptase inhibitor, interacts with the aromatic ring of tyrlSl via a 7r-aryl interaction which is presumably favorable to binding. ... 

It is not necessary to go through the whole exercise of setting up the molecular orbitals of cyclobutanes, which show many of the same features as cyclopropanes, only less so. Cyclobutanes also show enhanced reactivity over simple alkanes, but they are less reactive towards electrophiles, and cyclobutyl groups are less effective as stabilising substituents on electron-deficient centres than cyclopropyl groups. 

Isomerization of diastereomeric alkylzirconiums formed from reaction of (jj -Cp)2ZrHCl and a-pinene is implied in one instance , but such epimerizations are not confirmed in other systems . A vicinal cyclopropyl group influences the stereoiselec-tivity of hydrozirconation by intramolecular electronic effects (Eq. e). 

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