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Cyclopropanes alkyl-substituted—

The pattern of bond cleavage in the hydrogenolysis of aziridines generally follows that observed with cyclopropanes. Alkyl substituted aziridines are cleaved at the most accessible C-N bond. This provides a good route to the production of molecules having a primary amine group on a tertiary carbon (Eqn. 20.48). ... [Pg.533]

Danishefsky and co-workers have continued their investigations on the nucleophilic cleavage of activated cyclopropanes. Alkyl-substituted cyclopropane diesters (210) show a preferance for cleavage of the C-1—C-2 bond, with the alkyl... [Pg.52]

Asymmetric versions of the cyclopropanation reaction of electron-deficient olefins using chirally modified Fischer carbene complexes, prepared by exchange of CO ligands with chiral bisphosphites [21a] or phosphines [21b], have been tested. However, the asymmetric inductions are rather modest [21a] or not quantified (only the observation that the cyclopropane is optically active is reported) [21b]. Much better facial selectivities are reached in the cyclopropanation of enantiopure alkenyl oxazolines with aryl- or alkyl-substituted alkoxy-carbene complexes of chromium [22] (Scheme 5). [Pg.65]

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... [Pg.165]

In 1998, Saigo et al. [150] discovered the Rh(I)-catalyzed allenic version of the vinylcyclopropane rearrangement. With a subsituent on the cyclopropane ring two different isomers can be formed depending on which of the different allylic C-C bonds in the three-membered ring is broken. Depending on R2, different regioselec-tivites were obtained with 250. Alkyl-substituted substrates lead to 251 and aryl-substituted substrates to 252 (Scheme 15.79) [150]. [Pg.916]

Anodic oxidation of alkyl substituted cyclopropanes and spiroalkanes in methanol/TEATos (tetraethyl ammonium tosylate) affords monomethoxy and dimethoxy products in yields ranging from 6 to 86% [30, 31]. The products result from the cleavage of the most highly substituted C,C bond. In contrast to the anodic cleavage the acid-catalyzed cleavage occurs selectively at the less substituted carbon. The cleavage of hetero-substituted cyclopropanes is reported in Ref [32-35]. [Pg.132]

The structural isomerization of a number of alkyl substituted cyclopropanes has been investigated. In all cases the reaction is probably unimolecular. In general several olefins are formed. The results obtained are shown in Table 2. It is to be expected (especially if a diradical is an... [Pg.152]

In cyclopropanations with electrophilic carbene complexes, yields of cyclopropanes tend to improve with increasing electron density of the alkene. As illustrated by the examples in Table 3.5, cyclopropanations of enol ethers with aryldiazomethanes often proceed in high yields. Simple alkyl-substituted olefins are, however, more difficult to cyclopropanate with diazoalkanes. A few examples of the cyclopropanation of enamines with diazoalkanes have been reported [650]. [Pg.115]

The carbenoid from Et2Zn/CH2I2 [17], particularly when generated in the presence of oxygen [18], is more reactive than the conventional Simmons-Smith reagents. The milder conditions required are suitable for the preparation of 1-[16, 19] or 2-alkoxy-l-siloxycyclopropanes [20], which are generally more sensitive than the parent alkyl substituted siloxycyclopropanes (Table 2). Cyclopropanation of silyl ketene acetals is not completely stereospecific, since isomerization of the double bond in the starting material competes with the cyclopropanation [19]. [Pg.6]

Relatively few studies of the hydrogenation of substituted cyclopropanes are extant. From the studies which have been reported [26,248, 258], it would appear that, with alkyl-substituted cyclopropanes, ring cleavage occurs by rupture of the bond opposite the carbon atom carrying the greatest number of substituent groups. Thus in the platinum on... [Pg.102]

Deprotonation of (alkylcyclopropylidenemethyl)cyclopropanes (alkyl = methyl, cyclopropyl) with BuLi and subsequent reactions with various electrophiles afforded the corresponding ring-substituted methylenecyclopropanes (equation 295)365. When the lithiated compounds are treated with C02, carboxylic acids are obtained, together with isomeric lactones. These can be regarded as formal 3+2 adducts of the methylenecyclopropanes with C02 (equation 295)366. [Pg.620]

It was demonstrated in Section 3 that spiroannulation of cyclopropane to four- and higher-membered rings does not cause an increase in the strain energy of the molecule. It is not surprising, then, that the chemistry of these compounds does not differ from that of simple alkyl substituted cyclopropanes. Since exciting reviews on the chemistry of cyclopropanes are available42, the authors of this chapter will limit the description of properties of SPC of these types to some of their interesting applications. [Pg.869]

We said that the formation of cyclopropanes by addition of substituted carbenes to alkenes was rare—in fact, alkyl-substituted carbenes undergo very few intermolecular reactions at all because they decompose very rapidly. When primary alkyl halides are treated with base, alkenes are formed by elimination. Having read Chapter 19, you should expect the mechanism of this elimination to be E2 and, if you started with a deuterated compound like this, the alkene product would be labelled with two deuterium atoms at its terminus. [Pg.1069]

Cyclopropanation. Irradiation (350 nm.) of CH2I2 in the presence of alkenes yields the corresponding cyclopropane adducts with complete retention of stereochemistry. The reaction is facilitated by increasing alkyl substitution in contrast to the Simmons-Smith reagent, this reaction is not sensitive to steric factors. Presumably methylene ( CH2) is the reactive species. ... [Pg.90]

So far there is no evidence that simple alkyl substituted cyclopropanes undergo scrambling and exchange when opened with acid. On the contrary Deno 3D showed that opening of methylcyclopropane [30) with DCl leads exclusively to unrearranged product (Eq. (27)). [Pg.83]

Bridgehead carbons of adamantane [86], pinane [87], and fused norbornanes [85a, 88] undergo selective hydroxylation under similar reaction conditions. Alkyl-substituted cyclopropane is oxidized selectively at the a-position to cyclopropane ring (Eq. 3.54) [89]. The methyl group of toluene can be converted into the corresponding carboxylic acids (Eq. 3.55) [91]. [Pg.69]

More recently, Dinnocenzo and colleagues showed that a 2,3-dimethyl derivative (30, R = CH3) and several 1-phenyl- and l,l-diphenyl-2-alkyl-substituted cyclopropanes are captured with complete inversion of configuration [154, 155]. The observed stereochemistry requires an intermediate radical cation, 30, with the unperturbed stereochemistry of the parent molecule. This result unambiguously rules out a ring-opened cyclopropane radical cation in solution. [Pg.761]


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2-Substituted alkyl 3-

Alkyl cyclopropanes

Alkyl substitute

Cyclopropanes substituted

Cyclopropanes substitution

Substitution 1,2,3-substituted cyclopropane

Substitution alkylation

Substitution cyclopropanation

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