Other Reactions Involving Cyclopropane Rings

Other Reactions Involving Cyclopropane Rings. 2.2.1 SET Induced Reactions The radical cation of phenylcyclopropane can be obtained by irradiation in the presence of chloranil as the electron accepting sensitizer. ... 

Other reactions involving a-sulfonyl carbanions which afford cyclopropane derivatives or aromatic rings can be seen in the examples comprising Scheme 8392 400. 

The catalytic cycle proposed for the rhodium-porphyrin-based catalyst is shown in Fig. 7.18. In the presence of alkene the rhodium-porphyrin precatalyst is converted to 7.69. Formations of 7.70 and 7.71 are inferred on the basis of NMR and other spectroscopic data. Reaction of alkene with 7.71 gives the cyclopropanated product and regenerates 7.69. As in metathesis reactions, the last step probably involves a metallocyclobutane intermediate that collapses to give the cyclopropane ring and free rhodium-porphyrin complex. This is assumed to be the case for all metal-catalyzed diazo compound-based cyclo-propanation reactions. 

The reaction involving 0-hydroxyalkyl selenones is by far the less attractive route to qroxides among those cited above due to the difficulties usually encountered in the oxidation step and the easy rearrangement of the p-hydroxyalkyl selenones to carixmyl compounds (Scheme 184, b and c). This method is, however, particulariy useful for the synthesis of oxaspnopentanes (especially for those bearing a fully alkyl-substituted epoxide ring) ftom l-seleno-l-(r-hydroxyalkyl)cyclopropanes (Scheme 163, e Scheme 18S), which caruiot be obtained under other conditions. ... 

A number of cyclopropanes can be obtained by replacing one or several groups attached to a cyclopropane ring with other atoms or substituents. Many of these substitution reactions are two-step or multistep processes, which may involve base-induced generation of cyclopropyl anions that are quenched by an electrophile, formation under basic conditions of cyclopropenes which are trapped by a nucleophile, or generation of a cyclopropyl radical that undergoes subsequent reactions under neutral conditions. Formal substitution also takes place when cyclopropanes are converted to cyclopropylidenes which suffer l,n insertion, n > 3. Substitution reactions therefore cover a variety of compounds and a wide range of reaction conditions. 

Formation of a C-C bond to a cyclopropane ring at the expense of a C-Si bond is also achieved by acetylation of trimethylsilylcyclopropanes. Cyclopropyltrimethylsilane was converted to acetylcyclopropane (5) in 60% yield when treated with a mixture of acetyl chloride and aluminum(III) chloride in dichloromethane. "- Other compounds subjected to the same reaction conditions involve various (n- -3)-trimethylsilylbicyclo[n.l.0]alkanes. Some of these compounds undergo ring opening and give no cyclopropane whereas others afford complex reaction mixtures. Thus, when cxo-6-trimethylsilylbicyclo[3.1.0]hexane was acetylated as outlined above a 55 35 6 4 mixture of 6-acetylbicyclo[3.1.0]hexane (6), l-(2-chlorocyclopen-tyl)-propan-2-one (7), 2-acetyl-l-chlorocyclohexane (8), and l-(cyclopent-l-enyl)propan-2-one (9), respectively, was isolated in 94% total yield. 

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