Cyclopropanes conjugation with double

The pairs of p-nitrobenzoates, (299)/(300)243 and (30J)j(302)244 confirm electron release to the carbocation by conjugation with double bonds and cyclopropane rings, respectively. The comparison of (303) with (304)242> and (J05)245 demonstrates the analogous effect of double bond and cyclopropane participation in... 

In similar reactions, (12) with carbon—carbon double bonds that are conjugated with carbonyl groups gives cyclopropane derivatives (eq. 24) (48) ... 

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). 

Some remarks concerning the scope of the cobalt chelate catalysts 207 seem appropriate. Terminal double bonds in conjugation with vinyl, aryl and alkoxy-carbonyl groups are cyclopropanated selectively. No such reaction occurs with alkyl-substituted and cyclic olefins, cyclic and sterically hindered acyclic 1,3-dienes, vinyl ethers, allenes and phenylacetylene95). The cyclopropanation of electron-poor alkenes such as acrylonitrile and ethyl acrylate (optical yield in the presence of 207a r 33%) with ethyl diazoacetate deserve notice, as these components usually... 

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. 

Reduction of unsaturated aromatic aldehydes to unsaturated hydrocarbons poses a serious problem, especially if the double bond is conjugated with the benzene ring or the carbonyl or both. In Clemmensen reduction the a,)8-unsaturated double bond is usually reduced [160], and in Wolff-Kizhner reduction a cyclopropane derivative may be formed as a result of decomposition of pyrazolines formed by intramolecular addition of the intermediate hydrazones across the double bonds [280]. The only way of converting unsaturated aromatic aldehydes to unsaturated hydrocarbons is the reaction of... 

Reaction 15a is exothermic by (154.8 1.5) kJ moT1, and reaction 15b is exothermic by [157.1 ( >1.0)] kJ mol 1. From this, we conclude that vinylcyclopropane is stabilized relative to ethylcyclopropane by 157.1 - 154.8 = [2.3 ( >1.8)] kJ mol"1. In all three cases, we conclude that there is stabilization associated with vinylcyclopropane of some [3 ( >2)] kJ mol 1. Even with optimistic use of error bars (i.e. with the + sign), this stabilization value seems rather small. Yet, an altogether different documentation of the smallness of the double-bond cyclopropane conjugation is shown by the less than 1 kJ mol 1 difference in the enthalpies of formation of the isomeric bicyclo[4.1.0]hept-2-ene (35a) and bicy-clo[4.1,0]hept-3-ene (35b)51. 

Allen estimated that conjugation of a cyclopropane with an attached substituent was about 70% as effective as conjugation with a double bond45. This estimate is consistent with the 60% figure derived by Pete on the basis of an analysis of the UV spectra of cyclopropyl-containing systems53. 

This distortion is obviously caused by conjugation of the cyclopropane ring with the C=C double bond. This leads to a maximum interaction (orbital overlap) [50] in the bisected conformation which is apparent in the crystal structure of 3. 

Epoxylathyrol contains an extended conjugated system in which a cyclopropane ring is conjugated with the ix)8-unsaturated ketone. On photolysis the double bond undergoes a cis-trans isomerization followed by fragmentation... 

Bis(camphorquinone-a-dioximato)cobalt(II) (10) has been developed as a catalyst for enan-tioselective cyclopropanation reactions. It allows selective carbene transfer from diazoacetic esters to terminal C-C double bonds which are in conjugation with vinyl, aryl, alkoxycarbonyl or cyano groups, but not to alkyl-substituted alkenes, cycloalkenes, 1,3-dienes and al-lenes. The unusual chemoselectivity and some other experimental observations make the two mechanistic pathways proposed vide supra) questionable for these special carbene-transfer reactions. In contrast, the cobalt(II) complex 11 allows not only the cyclopropanation of styrene but also of oct-l-ene, a nonactivated alkene (ethyl diazoacetate, 35 °C, 3mol% of catalyst yield 50-60%). ... 

When isomerization of the double bond of the intermediate cyclopropene into the exo methylene position is energetically unfavored, double elimination followed by double addition of base can occur. Thus, reaction of (cu/tra i )-l,l-dichloro-2-methyl-3-vinylcyclopropane (9) with potassium terf-butoxide plus methoxide in dimethyl sulfoxide gave a mixture of cis- and trans-, -dimethoxy-2-methyl-3-vinylcyclopropane (10). Both double bonds formed via elimination appear to be conjugated with the vinyl group and do not migrate to the exo position. The similar reaction of l,l-dichloro-2-[( )-propenyl]cyclopropane (11) gave a small amount of 1-/ert-butoxy-2-(prop-2-enylidene)cyclopropane (13) in addition to products of double addition. Without added methoxide, 13 was the only product isolated. ... 

Cycloadditions to vinylcyclopropanes have been thoroughly reviewed. There are two reaction modes [27t- -27i] addition to the double bond and [27i-I-2bond conjugated with the 7t-bond. 

This paper deals with the polymerization of several purely hydro-carbonated and gem-dihalocyclopropanic monomers. The influence of conjugation between a cyclopropane and one double bond, and the influence of the conjugation between two cyclopropanic groups is shown for several monomers, such as spiropentane, vinyl gem-dihalocyclopro-pane, and bicyclononene. 

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