Cyclopropyl groups

For a review of various descriptions of the bonding in cyclopropane, see A. de Meijer, Angew. Chem. Int. Ed. Engl. 18 809 (1979) K. B. Wiberg, in The Chemistry of the Cyclopropyl Group, Z. Rappoport, ed., John Wiley Sons, New York, Chapter 1, 1987 B. Rozsondai, in The Chemistry of the Cyclopropyl Group, Vol. 2, Z. Rappoport (ed.), John Wiley Sons, New York, Chapter 3, 1995. 

In ion D, in which the phenyl group would be expected to be coplanar with the cationic center to maximize delocalization, the observed angle is 25-30°. This should permit effective benzylic stabilization. The planes of the cyclopropyl groups in both structures are at 85° to file plane of file trigonal carbon, in agreement with expectation for the bisected... 

Solvolysis rate studies also indicate that there is greater stabilization by a cyclopropyl group in a bisected geomeby. In tosylate 1, the cyclopropane ring is locked into an orientation which affords a perpendicular arrangement. It reacts 300 times more slowly than the model compound 2. Tosylate 3, which corresponds to the bisected geomeby, undergoes acetolysis at least 10 times faster than the model 2-adamantyl tosylate 4. ... 

The chemistry of organic selenium and tellurium compounds (2 volumes) The chemistry of the cyclopropyl group... 

Cyclopropylmethyl cations are even more stable than the benzyl type. Compound 7 has been prepared by solution of the corresponding alcohol in 96% H2S04. Compounds 5, 6, and similar ions have been prepared by solution of the alcohols in FSO3H—SO2—SbFf." This special stability, which increases with each additional cyclopropyl group, is a result of... 

In contrast to the stability of cyclopropylmethyl cations (p. 222), the cyclopropyl group exerts only a weak stabilizing effect on an adjacent carbanionic carbon. ... 

In the present case, the Walsh orbital will overlap with the k orbital of the carbonyl group more efficiently than the (3-o orbitals because of agreement of orbital symmetry and the efficient overlapping. This out-of-phase motif (13) is consistent with retardation of syn addition with respect to the cyclopropyl group, that is, anti preference. 

Recently a reverse perturbation effect of a cyclopropyl group on facial selectivities was described in two bicyclic systems, bicyclo[2.2.2]octane 59 and norbomane (bicyclo[2.2.1]heptane) 60 [124]. Bicyclo[2.2.2]octene 59a, annulated with an exo-cyclopropyl group, i.e., exo-tricyclo[3.2.2.0 ]non-6-ene, and 7-methylenenor-bomane 60a, annulated with an exo-cyclopropyl group, i.e., 8-... 

The anti facial preference of the norbomane 60a was previously found in the additions of dichlorocarbene (syn anti = 44 56) [125, 126] and of 9-BBN (symanti = 11 89) [125, 126]. The anti-preference was also observed in the reactions of methylidenebicyclo[2.2.1]heptane (60b) bearing an enrfo-dimethylcyclopropyl group (Rj,R2=C(CH3)2) [125, 126] with dichlorocarbene (symanti = 34 66) and 9-BBN (syn anti = 5 95). Therefore, we can conclude that the anti-preference, induced by a cyclopropyl group, is intrinsic to 7-methylidenenorbomane 60a. The anti preference was also observed in alkyl-substituted 46d (R = Rj = Et), supporting the idea that a cyclopropyl group behaves as an electron-donating substituent [78]. 

This notion is also snpported by the following experimental observations. Because substitution of a cyano gronp on the cyclopropane ring lowers the energy of the Walsh orbital of the cyclopropyl group, the resultant attennation of the interaction of the olefin orbital with the Walsh orbital, if this interaction is indispensable, would reduce the facial selectivity. However, substitution of a cyano gronp on the cyclopropyl group, as in ejco-cyano 59c and endo-cymo 59d, essentially does not modify the syn-preference in dihydroxylation and epoxidation, but even increases the syn preference (59c (98 2) and 59d (>99 <1)) in the case of dihydroxylation. 

Figure 9 Structure of the immunogen hapten used to generate antibodies for a type I pyrethroid class-selective assay. Pyrethroids lacking an a-cyano group are generally termed type I. This hapten exposed the features most common to type I pyrethroids, the phenoxybenzyl group, the cyclopropyl group and the lack of a cyano group, resulting in antibodies that recognized permethrin, phenothrin, resmethrin and bioresmethrin, but not cypermethrin...

Researchers at the Vrije Universiteit of Amsterdam in collaboration with others [141] have investigated conformationally restricted forms of histamine. For example, constraining the side chain with a cyclopropyl group (67)... 

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