Cyclopropyl system

Write out the ehitrge density diagTiiiiis for the positive ion. free radical, and negative ion of the cyclopropyl system. 

Fonnation of allylic products is characteristic of solvolytic reactions of other cyclopropyl halides and sulfonates. Similarly, diazotization of cyclopropylamine in aqueous solution gives allyl alcohol. The ring opening of a cyclopropyl cation is an electrocyclic process of the 4 + 2 type, where n equals zero. It should therefore be a disrotatory process. There is another facet to the stereochemistry in substituted cyclopropyl systems. Note that for a cri-2,3-dimethylcyclopropyl cation, for example, two different disrotatory modes are possible, leading to conformationally distinct allyl cations ... 

Moriwaki et al. studied the photochemical behavior of various substituted homonaphthoquinones under PET conditions using amine and arene compounds as electron donors. Thereby, the main reaction path found was the opening of the cyclopropyl system, following dimerization [18]. 

The electrochemical rednction at GC electrodes in ACN of a nnmber of organic bromides (mainly with cyclopropyl systems), nsed as radical clocks in reactions of the... 

Explain the rate ratio for compounds 3 and 4 estimated for limiting SN1 solvolysis by correcting the cyclopropyl system for anchimeric assistance which occurs when the ring opens. 

The placement of the methyl group between the two carbons (so to speak) produces a cyclopropyl system. The simplest example is 2-phenylcyclopropyl-amine, a drug with the generic name of tranylcypromine and the trade name Parnate. It is a mono-amine oxidase inhibitor and has been marketed as an antidepressant,... 

This band often appears as a doublet probably resulting from the accidental degeneracy of an overtone of another low-lying vibration mode (Fermi resonance). 7a, 6 8) The C—H stretching vibrations also undergo a high-frequency shift and appear at 3050 cm-1, a position generally characteristic of the methylene stretch in cyclopropyl systems.67)... 

On the other hand, solvolysis of the tosyl derivative of 1-cyclopropyl-cyclopropanol (112) in aqueous ethanol does not lead to ring enlarged products. 91 Apparently, the incipient cyclopropyl cation is better stabilized by conjugative interactions with another cyclopropyl system than with a vinyl group. 

The proposed mechanism involves silver-catalyzed attack by the imine function on the cyclopropyl system. This is followed by conjugate addition of the intermediate silver species on the tropone ring system and subsequent isomerization to afford 171. 

Overall, a-, / - and -functionalization is possible with the various silyl substrates reported in this section. In a formal sense, the relevant reactions discussed correspond to an umpolung of reactivity of the enolic or cyclopropyl systems, as depicted schematically below [22] ... 

In small, fused cyclopropyl systems, only the disrotatory mode that moves the bridgehead hydrogens outward is geometrically feasible. This means that the... 

An intriguing combination of two cyclopropyl systems allows cyclobutanone formation according to equation 105 base-induced fragmentation of an intermediate cyclobutanol stereoselectively forms a functionalized olefin . 

Brown and coworkers have published several papers concerning solvolyses of 1-aryl-1-cyclopropyl 3,5-dinitrobenzoates in 80 % aqueous acetone. A plot of log k versus <7 revealed, by its non-linearity, a change in mechanism as electron demand at the cationic center increases. The more electron-releasing substituents give more unrearranged cyclopropyl product. Thus the cyclopropanol to allyl alcohol ratios were p-MeO, 87 13 p-MeS, 70 30 and p-Me, 5 95. Extrapolation of the tertiary data to the parent cyclopropyl system indicates that solvolysis of the latter must be enhanced by concerted ring-opening by a factor of 10. ... 

An exception to the tetra-substitution requirement is exhibited by cyclopropyl systems which carry a r-Bu group geminate to the reactive C-H group (equation 10) . In this... 

Total loss of optical activity of the cyclopropyl radical was also reported recently by Walborsky et al. [22] for a chiral aliphatic cyclopropyl system. When optically pure (S)-( -1- )-l-bromo-l-methylspiro[2.5]octane 19 was reduced under homogeneous conditions with lithium naphthalenide in tetrahydrofuran (THF) at room temperature the resulting acid 22, isolated after carbonation. was completely racemic (Scheme 5). 

As may be readily appreciated from the foregoing examples, substitution reactions on cyclopropyl systems and their derivatives may take some unexpected routes and lead to a variety of interesting products. Which pathway will actually be followed, or more realistically, what will be the spread of products, may be only determined by performing the experiment and identifying the products. The value of the mechanistic approach is that it will... 

On the other hand, isolable transition-metal-bound cyclopropyl systems can also be used in coupling reactions. Thus bis(cyclopentadienyl)bis(cyclopropyl)titanium reacted, in a Tebbe-type transformation, with carbonyl compounds to give methylenecyclopropanes 3 and with alkynes to form vinylcyclopropanes 4 via carbonyl olefination. ... 

When a second activating function such as phenyl or benzoyl was introduced into the cyclopropyl system, sodium was capable of cleaving the cyclic C-C bond. ... 

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