Of cyclopropyl halides

Several studies of the electrochemical reduction of cyclopropyl halides have been reported in the literature 20,26,27,55) t it appears that reduction occurs without complete loss of stereochemical integrity. The predominent stereochemical pattern involves reduction with overall (partial) retention of configuration. The following examples are representative ... 

The partial loss of configuration often observed during reduction of cyclopropyl halides may actually occur via the corresponding cyclopropyl radicals, which lose configuration rapidly °>. In that event, their behavior would resemble that of vinyl halides, as exemplified by the 3-iodo-3-hexenes 16>. Occasional cases of partial inversion could be associated with shielding of the cyclopropyl carbanion by the electrode surface, with concomitant protonation on the other face of the carbanion S8>. 

As was indicated previously, several other parameters can affect the stereochemistry of reduction of cyclopropyl halides 20>. For example the optical purity of 59 produced from the electrochemical reduction of 58 in acetonitrile... 

B. Electron Transfer to a Bonds of Cyclopropyl Halides 1. Surface reactions. ... 

SCHEME 13. Alkali metal naphthalenide reductions of cyclopropyl halides... 

The formation of cyclopropyl halide radical anion pairs as intermediates is also invoked in Sr I type substitution reactions by Rossi and Meijs . It seems that the photostimulated reaction of cyclopropyl bromides like 7-bromonorcarane (120) with Ph2P M to give 121 involves a radical chain, and halogen-containing radical anions as chain carrier. 

The electrochemical reduction of cyclopropyl halides has been widely investigated mainly in relation to its stereochemistry. No ring-opened products have been reported yet but substitution of the halogen by a hydrogen usually proceeds in high yields. Both monohalocyclopropanes, mostly bromide derivatives, and gem-dihalocyclopropanes were investigated. Several groups have studied the stereochemistry of the electroreduction... 

Scheme 4.17 Reduction of cyclopropyl halides with calcium reagents in different forms...

The course of this reaction is similar to those ol Grignard reactions of cyclopropyl halides, with the large amounts of c and s again precluding a value of k (D model) that could account for the... 

The products are consistent with mechanisms similar to those that are viable for reactions of cyclopropyl halides (Section 7.2.9). If the D model describes the non-getninate pan of ptithway R, then the values of 6 and t must be similar to those for typical alkyl and cyclopropyl radicals (Sections 7.2.8-7 2.9). 

Formation of allylic products is characteristic of solvolysis reactions of cyclopropyl halides and arenesulfonates. Similarly, diazotization of cyclopropylamine in aqueous media gives only allyl alcohol. In a few instances, products containing an intact cyclopropyl ring have been reported, but these are special cases in which either the cyclopropyl cation is especially stabilized or the ring-opened allyl cation especially destabilized. Apart from these, the ring-opening of cyclopropyl cations to... 

Elimination reactions of cyclopropyl halides can provide a simple route to cyclopropenes, since the former are readily available by semi-reduction of the dihalogeno-carbene adducts of olefins. An example is shown in Scheme 15. ... 

The selection rules for electrocyclic ring-openings can also explain rate differences in the solvolysis of cyclopropyl halides as a function of stereochemistry. For example, shown in... 

Solvolysis of cyclopropyl halide to give acyclic carbocation can also be explained by PMO-method. Here backside attack of opening o-bond electrons on C—X bond takes place in transition state which is aromatic, therefore, reaction is thermally allowed. This process is illustrated below ... 

A review of the stereochemical consequences of electrochemical reduction including dehalogenation of cyclopropyl halides has been published. " Polaro-graphic reduction proved to be the most convenient method of introducing hydrogen (or its isotopes) into (305). ... 

It was reported last year that the stereospecificity of tri(n-butyl)tin hydride reduction of cyclopropyl halides is dependent upon the other substituent present at the reaction site, i.e. the ability of the substituent to stabilize the radical or affect its geometry. Norcarane derivatives (618) have been made by standard methods and reduced with HSnBu3 under a variety of experimental... 

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