A-Cyclopropyl substituted

A Ru-Josiphos catalyst was highly selective for the hydrogenation of an intermediate for an anthrax lethal factor inhibitor with a tetra-substituted C=C bond, as depicted in Figure 37.8 (Merck [44]). Rh-Josiphos (Lonza [42]) and Rh-Bo-Phoz (Eastman [45]) catalysts were effective for the hydrogenation of an exocy-clic and a cyclopropyl-substituted C=C bond. 

Further reduction in R leads to the point Rc (Figure 3) at which the bond is fully formed and normal cyclopropyl substituent interactions occur. Homoconjugation ceases to be a relevant chemical factor at point Rc and the molecule can be adequately described in terms of a cyclopropyl substituted system. 

Of special interest for the present review is the study of the solvolysis of the a-cyclopropyl-substituted cyclopropylidenemethyl bromide This system, which... 

Another interesting alkene synthesis starts from a cyclopropyl-substituted alcohol, which, on reaction with magnesium halides, is converted to a haloalkene MesSiX has also been used in this type of reaction (Scheme 22). ... 

Similarly, in the intramolecular version, bicyclic cyclobutanones can be formed. If the carbene unit bears a cyclopropyl substituent, a cyclopropyl-substituted cyclobutanone was obtained, e.g. formation of 9. °... 

Photochemical conversion of an amino(cyclopropyl)carbene (obtained from cyclopro-pyl(methoxy)carbene with optically pure D,i.-erythro amino alcohols) gave a cyclopropyl-substituted lactone, e.g. formation of 13, which upon hydrogenolysis gave a chiral cyclopropyl-glycine system.The reaction proceeds via a ketene complex. 

The (cyclopropylamino)carbene complex 15 reacted with diphenylalkyne to give a nitrogen ylide, which was converted via thermal A -cyclopropyl to C-cyclopropyl rearrangement and decomplexation to a cyclopropyl-substituted lactam. 

Pentacarbonyl[cyclopropylethynyl(ethoxy)carbene]chromium complex 19 reacted with cyclo-penta-1,3-diene to give a cyclopropyl-substituted carbene complex of norbornadiene 22, which was converted to the corresponding carboxylic acid 23 upon oxidation or to a 1,4-quinone-type derivative 24 after Dotz-type cyclization with phenylethyne. ... 

Alkylidenecyclopropanes bearing a carbanion center in the side chain of the alkylidene group react with iodobenzene in the presence of catalytic amounts of a palladium(0) complex to give various compounds depending on the chain length between the carbanion center and the alkylidene group. With a one-carbon chain vinylcyclopropanes are formed via intramolecular carbanion attack of an intermediate allyl system, with two- and four-carbon chains cyclohexenes or vinylcyclohexanes are formed, while with a three-carbon chain a cyclopropyl-substituted cyclopentane ring is obtained. 

Klaer A, Saak W, Haase D, Muller T (2008) Molecular structure of a cyclopropyl substituted vinyl cation. J Am Chem Soc 130 14956... 

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 ... 

Reaction of the cyclopropyl-substituted pivalate (25) with dimethyl benzylidenema-lonate in the presence of a palladium catalyst gave a mixture of alkylidenecyclo-propane (26) and vinylcyclopropane (27). The ratio of these two adducts is found to be quite sensitive to the choice of ligand and solvent. While triisopropyl phosphite favors the formation of the methylenecyclopropane (26), this selectivity is completely reversed with the use of the bidentate phosphite ligand dptp (12). Interestingly there was no evidence for any products that would have derived from the ring opening of the cyclopropyl-TMM intermediate (Scheme 2.8) [18]. 

We have previously seen (p. 437) that this is the reason nucleophilic substitutions are not feasible at a cyclopropyl substrate. The reaction is often used to convert... 

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]. 

Besides the carbocations mentioned above, numerous highly stable carboca-tions have been isolated as the salts of inorganic anions. Azulene analogues of triphenylmethylium ion [ll ]-[20 ], [21 j, [22 " ] and [23 j trisubsti-tuted cyclopropenylium ions [l" ] and [24 ]-p6 ] cyclopropyl-substituted tropylium ions [27 ]-[30 ] tropylium ions annelated with bicyclic frameworks [31 ]-[36 ] and [37 ]-[39 ] fulvene-substituted cyclopropenylium [40 ] and tropylium [41 ] ions a tropylium ion condensed with acenaphthylene [42 ] and a cation containing a 147t periphery [43 ] have... 

Replacement of the ethanolamine head group is also well tolerated. Substitution with a cyclopropyl (243) [37], allyl (244) or propargyl group (245) [164] all led to an increase in binding affinity compared to AEA. Replacement of the head group with aromatics is also allowed. The phenyl derivative (246) retains affinity at the CBi receptor [37], whereas the 2-substituted A-methyl pyrrole (247) has a 2-fold improved affinity compared to AEA [167]. Interestingly, the 3-substituted furan derivative (23) that has micromolar affinity for the AEA transporter (see above) does not bind to the CBi receptor, but has good affinity for the CB2 receptor [167]. These results are summarised in Table 6.20. 

Cu(II) EPR signal in nitriles as solvent as well as by polarographic measurements 144>. Similarly, the EPR signal disappeared when Cu(OTf)2 was used for catalytic cyclo-propanation of olefins with diazoesters 64). In these cases, no evidence for radical-chain reactions has been reported, however. The Cu(acac)2- or Cu(hfacac)2-eatalyzed decomposition of N2CHCOOEt, N2C(COOEt)2, MeCOC(N2)COOEt and N2CHCOCOOEt in the presence of cyclopropyl-substituted ethylenes did not furnish any products derived from a cyclopropylcarbinyl - butenyl rearrangement128. These results rule out the possible participation of electron-transfer processes and radical intermediates which would arise from interaction between the olefin and a radical species derived from the diazocarbonyl compound. 

The allene 149 gave by reaction with maleic anhydride (entry 1) and N-phenylmaleimide (entry 2) the [2 + 2] adducts 155a, b as mixtures of two diastereoisomers [36], Nevertheless, their chemical yield was very low and competitive reactions, mostly [4 + 2] cycloadditions on a rearranged al-lylidenecyclopropane and on a primary 1 1 adduct derived from an ene reaction (see Sect. 2.1.2), prevailed. Allenes 149 and 563 cycloadded to tetracyano- and l,l-bistrifluoromethyl-2,2-dicyanoethylene (Table 45, entries 3-6) also selectively at the cyclopropyl substituted double bond in order to remove most of the ring strain [149a],... 

Surprising is the absence of evidence for additional stability of 85 over 83. Electron donation from the electron-rich a bonds of the cyclopropyl ring to the carbene s vacant p orbital is widely believed to stabilize cyclopropylcarbenes.4 One would therefore expect 85, with an additional cyclopropyl substituent, to react more slowly than either parent carbene 83 or dimethylcarbene, but all three lifetimes are comparable. The lifetimes of 83-85 need to be redetermined in inert (fluorocarbon) solvents in order to reveal their innate differences. Note, however, that the effect of cyclopropyl substitution is apparent upon comparison of 83 (r 24 ns) to MeCH (r < 0.5 ns).89110... 

More recently, the bis-cyclopropanation of dienyne 325 has also been investigated by Fensterbank, Malacria, and Marco-Contelles to construct highly strained cyclopropyl-substituted diquinane frameworks 327 in a completely diastereoselective manner (Scheme 84). 3 It is noteworthy that the formal metathesis product was also observed in these reactions, albeit as a minor product, and that a simple introduction of a methyl group to one of the two ene moieties substantially affects the reaction. 

The -conformation 13 is lower in energy than the Z-isomer 14. These are the smallest cyclopropyl substituted carbocations which can be investigated in solution by high resolution NMR. The corresponding primary cyclopropylmethyl cation 15 cannot directly be observed by high resolution NMR in solution because it is energetically less favorable than the bicyclobutonium ion 16 and thus only a minor isomer in the fast dynamic equilibrium of the cations 15 and 16. 13C- and H... 

A-cyclopropyl- and N- Xhy -N-(substituted phenyl)aminomethylene-malonates were cyclized in polyphosphoric acid [89EUP332033, 89JAP(K)83068], in ethyl polyphosphate (89USP479490), and in phospho-ryl chloride (89EUP304158). 

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