Cleavage of cyclopropanes

Tl(III) < Pb(IV), and this conclusion has been confirmed recently with reference to the oxythallation of olefins 124) and the cleavage of cyclopropanes 127). It is also predictable that oxidations of unsaturated systems by Tl(III) will exhibit characteristics commonly associated with analogous oxidations by Hg(II) and Pb(IV). There is, however, one important difference between Pb(IV) and Tl(III) redox reactions, namely that in the latter case reduction of the metal ion is believed to proceed only by a direct two-electron transfer mechanism (70). Thallium(II) has been detected by y-irradiation 10), pulse radiolysis 17, 107), and flash photolysis 144a) studies, butis completely unstable with respect to Tl(III) and T1(I) the rate constant for the process 2T1(II) Tl(III) + T1(I), 2.3 x 10 liter mole sec , is in fact close to diffusion control of the reaction 17). 

Oxidative cleavage of cyclopropanes has been studied mostly with lead(IV), thaIlium(III) and chromium(Vl) reagents. - The oxidative cleavage of cyclobutanols has been explored mainly with chro mium(VI) reagents, although other oxidants have been studied. ... 

Due to these restrictions mechanistic investigation of the cleavage of cyclopropanes as well as preparation of cyclopropane derivatives (see Chapter 7) will not be discussed here. Obviously the author s personal view regarding synthetic utility could not entirely be excluded and may have influenced the choice of examples presented. 

Cyclopropyl radicals, anion radicals and anions 2. Reductive cleavage of cyclopropanes... 

Reductive cleavage of cyclopropane rings. Cyclopropanes can be seductively cleaved by solutions of an alkali metal in liquid ammonia if a carbonyl group (example I),1 a carboxylate group (example II),2 or a phenyl group (example III)3 is attached to the cyclopropyl ring. 

Cleavage of cyclopropanes. In the absence of a solvent, cyclopropanes are reductively cleaved by diborane. Thus norcarane heated with diborane at 100 for 1-2 hrs. gives the alkylborane (2), identified by peroxide cleavage to cyclohexyl-methanol (3). No reaction occurred in tetrahydrofurane. 

Cleavage of cyclopropanes. Ouellette found that thallium triacetate cleaves phenylcyclopropane to give essentially a single product, 1-phenyl-1,3-diacetoxy-propane (6). Analysis (v.p.c.) showed the presence of only a trace of trans-cvsmamyX... 

Other examples of C-C bond cleavage of cyclopropane derivatives like cyclo-propene, benzocyclopropane, bicyclo [1.1.0] butane, bicyclo [2.1.0] pentane, meth-ylenecyclopropane, and vinylcyclopropane have been reviewed comprehensively [19-23]. 

Metallacyclic complexes play an important role as reactive intermediates in catalytic cycles initiated by homogeneous transition-metal complexes. Thus, metallacyclobutanes are discussed as intermediates in alkene metathesis, isomerization of strained cyclopropane compounds and many other reactions. On the other hand, numerous examples of isolable me-tallacyclobutane complexes have been reported. These can be formed by different routes such as carbon-carbon bond cleavage of cyclopropane compounds (A), cyclometallation via C — H bond cleavage (B), nucleophilic addition to allyl complexes (C), rearrangement of metallacyc-lopentanes (D) or transmetalation of 1,3-dimetallalated carbon chains (E). ... 

Lithium is the preferred metal for the reductive cleavage of cyclopropane bonds in cyclopropyl ketones. Sodium is less suited for this reaction because it tends to reduce the carbonyl group rather than open the three-membered ring. With sodium the cyclopropane ring in methyl-substituted benzoylcyclopropanes 1 was retained and the benzoyl group reduced to benzyl contrary to lithium which gave rise to the formation of cleavage products. ... 

The acid-catalysed cleavage of cyclopropanes has been extended by use of mercuric acetate as an alternative electrophilic reagent. 3(x,5a-Cyclocholestane... 

Cleavage of cyclopropanes. Trost et al. have disclosed a new method for synthesis of the acyclic C7 side chain characteristic of steroids and some other natural products. The key step involves cleavage of a cyclopropane ring with dimethylcopperlithium, (1) (2). Tlie paper cites some relevant references to cleavage of cyclopropane rings with organocuprates. 

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