Cyclopropane moieties

An example, where two C-C-bonds are formed and one C-C-bond is broken is the synthesis of the tricycle 3-285, which has some similarity with the eudesmane framework 3-286, developed by Kilburn and coworkers (Scheme 3.72) [113]. Thus, exposure of the easily accessible methylenecyclopropyl-cyclohexanone 3-281 to samarium(II) iodide led to the generation of ketyl radical 3-282, which builds up a six-membered ring system with simultaneous opening of the cyclopropane moiety. Subsequent capture of the formed radical 3-283 by the adjacent alkyne group afforded the tricycle 3-285 via 3-284 as a single diastereoisomer in up to 60% yield. It should be noted that in this case the usual necessary addition of HMPA could be omitted. 

Nenajdenko et al. described the first example of addition of a 1,2-dication to C-C mutiple bonds. The only S-S dication found to participate in this reaction was the highly strained dication 115 derived from 1,4-dithiane. The reaction with alkenes 119 proceeded under mild conditions and led to derivatives of dithioniabicyclo[2.2.2]octane 120 as shown in Equation (33) and Table 21 <1998JOC2168>. This reaction was sensitive to steric factors and proceeded only with mono and 1,2-disubstituted ethylenes. Only alkenes conjugated with aromatic or cyclopropane moieties underwent this reaction. For the 1,2-disubstituted alkenes used in this study, the relative configuration of substitutents at the double bond was preserved and only one diastereomer was formed (see entries 2 and 3). 

Reaction with alkenes is sensitive to steric factors - in the case of dication 49, only reaction with mono- and 1,2-disubstituted ethylenes afforded identifiable reaction products. Only alkenes conjugated with aromatic or cyclopropane moiety undergo this reaction. In the case of 1,2-disubstituted alkenes, the relative configuration of substitutents at the double bond is preserved and only one diastereomer is formed. 

A special case is met when the substituent is the cyclopropyl group, because of the presence of high-lying almost 7r-type cr-orbitals. These orbitals, Wa and Ws, shown schematically in diagram 36, have been introduced by Walsh180 to explain the properties of molecules containing the cyclopropane moiety. 

In addition to siloxy- and alkoxy-substituted VCPs, alkyl- and H-substituted VCPs are also effective in the intermolecular [5 + 2]-cycloaddition reaction (Scheme 11). In general, an increase in the steric bulk of the cyclopropane substituent (H vs. Me vs. Pr1) leads to increased reaction rates, putatively through preferential population of the more reactive as-oid arrangement of the vinyl and cyclopropane moieties.43... 

Because the chiral cyclopropane subunit is present in a wide range of natural and synthetic products showing important biological properties, asymmetric construction of the cyclopropane moiety via asymmetric cyclopropanation is of commercial interest. Many chiral catalysts and chiral ligands have been pre-... 

Applying only a few simple operations, the dibenzylaminocyclopropanes 133-R, prepared as described above from N,N-dibenzyl-a-benzyloxyacetamide in 33—48% yield (see Scheme 11.16 and Table 11.9), have been transformed into N-Boc-protected methyl esters of amino acids 138-R containing a cyclopropane moiety (Scheme 11.35) [109,110], Several such analogues of natural amino acids, also referred to as methanoamino acids, exhibit important biological activities [128],... 

Clear downfield 8-SCSs (+ 1.3 to + 2.9) were also observed in 4-substituted tricyclenes 122, although they have no syn-axial orientation of X and the 8-carbon atom (154). Possibly, the transmission of the 8-SCS is modulated by the intervening cyclopropane moiety (154). 

This wide range of transformations includes many reactions which are one way or another connected with cyclopropane derivatives. The cyclopropane moieties can be part of the structure of both the linear dienes or of annulated polycyclic unsaturated systems as well as being part of a spiro compound. 

Photolytic. Photolysis of permethrin in aqueous solutions containing various solvents (acetone, hexane, and methanol) under UV light (1 >290 nm) or on soil in natural sunlight initially resulted in the isomerization of the cyclopropane moiety and ester cleavage. Photolysis products identified were 3-phenoxybenzyldimethyl acrylate, 3-phenoxybenzaldehyde, 3-phenoxybenzoic acid, mono-chlorovinyl acids, cis- and fra/is-dichlorovinyl acids, benzoic acid, 3-hydroxybenzoic acid, 3-hydroxybenzyl alcohol, benzyl alcohol, benzaldehyde, 3-hydroxybenzaldehyde, and 3-hydroxybenzoic acid (Holmstead et ah, 1978). 

The cyclopropane moiety is a fundamental class of functional group present in both natural products and numerous therapeutic agents. It has provided the impetus for significant breakthroughs in the use of metal carbenoids [151] and organocatalytic ylide intermediates [152, 153] such that rehable methods exist for most disconnective strategies on this ring system. 

This transformation of alkyl 2-chloro-2-cyclopropylideneacetates has been applied for the preparation of compounds of type 83 containing a czs-configurated disubstituted cyclopropane moiety [25] with potential liquid crystalline properties [52]. In the first approach to such compounds, 2-chloro-2-cyclopropylide-neacetic acids 2b-H, 2i-H were coupled with the linear diaryl components 81 fol-... 

Other systems studied include the spiroheptadiene system (13) in which the cyclopropane moiety lies in the nodal plane of the butadiene HOMO [1 2,9 10]bis-methano[2.2]paracyclophane (15), in which two cyclopropane moieties are joined with two benzene rings in such a way that tertiary-tertiary cyclopropane bonds lie parallel to the aromatic n system 7-methylenequadricyclane radical cation (16 ), in which a pair of cyclopropane groups lie orthogonal to an olefinic moiety and the 7-spirocyclopropanenorbomadiene radical cation (18 ), in which a pair of nonconjugated ethene groups and a cyclopropane moiety are joined. 

While the nuclei of the aromatic segments show the identical signal directions, the cyclopropane protons show characteristic differences. This suggests significantly different spin-density distributions for the cyclopropane moieties of the two species and, thus, different structures. Like the norcaradiene HOMO, the styrene HOMO is antisymmetric at the positions of attachment, suggesting preferred interaction with the antisymmetric cyclopropane HOMO. In the norcaradiene system, the natural structure ( Aj) of the cyclopropane radical cation is altered by the interaction with the diolefin entity. 

In the case of spiroheptadiene (13), the cyclopropane moiety lies in the nodal plane of the butadiene HOMO, causing the interaction with either cyclopropane HOMO to be negligible. On the other hand, the dibenzo derivative of 13, spirofcy-... 

In another study involving C78, a pure sample of the C2v isomer was prepared using the cyclopropanation-retro-cyclopropanation reaction sequence [44, 64]. This reaction scheme consists of a controlled potential electrolytic (CPE) reduction of a previously synthesized cyclopropane derivative of the isomer, leading to removal of the cyclopropane moiety (s), (see Sect. 6.1.5). A pure sample of the D3 isomer was obtained by high performance Kquid chromatography (HPLC) as previously described [49, 65]. The redox behavior of both isomers, in DCM at room temperature, reveals that their cathodic electrochemistry is indeed very similar (although not identical) in this solvent [44]. The first two reductions are easier for the D3 isomer by 60 and 100 mV, respectively, while the third and fourth reductions are nearly identical for the two... 

Analogous treatment of 22 furnished (l/ ,2S)-23, i.e., the enantiomeric cyclopropane moiety, with equally high yield and stereoselectivity. 

For radical cations of norcaradiene and derivatives, the interaction of the cyclopropane in-plane e orbitals with the butadiene frontier MO favors the type B structure. The assignments are based on ab-initio calculations, CIDNP results, and the ET photochemistry. The norcaradiene radical cation (lla ) has a electronic ground state (Cj symmetry). The Cl—C6 bond is shortened on ionization (—3.4 pm) while the lateral bonds are lengthened (+2.8 pm). The delocalization of spin density to C7 (py = 0.246 py 5 = 0.359) and the hyperfine coupling constants of the cyclopropane moiety a e = 1.36 mT oysyn = —0.057 mT flvanti = —0.063 mT) support a type B structure. 

However, 2-bromotetradeca-l,13-dien-7-ynes such as 96 n = 1), which were set up to furnish decahydrophenan-threne skeletons (6-6-6-tricycles), gave the interesting tetracyclic compounds 97 (n=l) with a cyclopropane moiety bridging the A- and B-ring junction (Scheme 27). " " ... 

Skatteb0l rearrangements in more complex dibromo-vinylcyclopropanes have also been reported. Thus, either a system consisting formally of two double bonds and one dibromocyclopropane unit or an educt containing two dibromo-cyclopropane moieties and one double bond undergo several carbene-carbene isomerizations upon treatment with methyllithium. In both cases, complex product mixtures arise. 

The same authors have demonstrated that 1,3-diynes behave in predictable yet distinctive manners compared to simple enynes under electrophilic transition metal-mediated reaction conditions. This characteristic behaviour of 1,3-diynes is presumably caused by the slightly electron-withdrawing nature of the alkynyl substituent, which not only renders preferentially the formation of 5-exotype alkylidenes but also allows for the subsequent [l,3]-metallotropic shift. Several salient features of reactions with this functionality include the following (a) an acetate is more reactive than the tethered alkene as an initiator, generating [l,2]-acetate migrated alkylidene intermediate, whereas an alkene is a better terminator than an acetate/bromide to generate the cyclopropane moiety (b) allene products are not formed at all under current reaction conditions (c) 5-exo/6-endo-type alkylidene formation depends on the heteroatom substituent in the tether (d) facile metallotropic [1,3]-shift of the intermediate alkylidenes occurred whenever possible. 

The [10 11] methano[3 2]paracyclophane system (108) [229] appears less strained than 107 yet more restricted than diphenylcyclopropane. The CIDNP effects observed are closer to that of ds-diphenylcyclopropane than to that of 107. Obviously, a large fraction of the strain inherent in 107 is relieved by substituting a trimethylene bridge for one of the cyclopropane moieties [229],... 

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