With Cyclopropyl Halides

Dimethyl ditellurium reacted with trichlorocyclopropenium salts and with tetrabromocy-clopropene to produce tris[methyltelluro]cyclopropenium salts. 

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The scope of transition metal-catalysed cross-coupling reactions involving N-tosylhydrazones has been broadened. While IV-tosylhydrazones cross-couple with trialkylsilylethynes to form C -C s bonds under Cu(I) catalysis,i° Pd(0) catalysis has been used to induce (i) their oxidative cross-coupling reactions with allylic alcoholsi and (ii) their cross-coupling with cyclopropyl halides, giving rise to... 

The key cyclization in Step B-2 was followed by a sequence of steps that effected a ring expansion via a carbene addition and cyclopropyl halide solvolysis. The products of Steps E and F are interesting in that the tricyclic structures are largely converted to tetracyclic derivatives by intramolecular aldol reactions. The extraneous bond was broken in Step G. First a diol was formed by NaBH4 reduction and this was converted via the lithium alkoxide to a monomesylate. The resulting (3-hydroxy mesylate is capable of a concerted fragmentation, which occurred on treatment with potassium f-butoxide. 

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>. 

A recent report has shown that tricyclopropylbismuth can be utilized in the cross-coupling reaction with aryl halides and triflates [57]. Representative examples are shown in Scheme 38. Addition of a base activator and excess of the bismuth reagents are necessary to obtain the coupling products in good yields, although more than one cyclopropyl group was transferred when 0.5 equivalents of... 

The cycloalkyl halides, except for cyclopropyl halides, have physical and chemical properties that are similar to those of the open-chain secondary halides and can be prepared by the same types of reactions (Table 14-5). All the cycloalkyl halides undergo SN2 reactions rather slowly and, with nucleophiles that are reasonably basic ( OH, OC2Hs, C=N, etc.), E2 reactions... 

The equilibria between the allyl and the cyclopropyl cations and the corresponding equilibria of the anions, are not seen as such, but they are found in disguise. Thus the cationic reaction is seen when cyclopropyl halides are heated or treated with silver ions. The cyclopropyl cation itself is not an intermediate, because the ring opening (4.23, arrows) takes place at... 

The unsymmetrical halonium ions such as 165-Br are found in equilibrium with open-chain [3-bromocarbenium ion. Many of the above-mentioned halonium ions have been prepared by the protonation of the appropriate cyclopropyl halides in superacids.390... 

Even cyclopropyl halides are reducible by LiAlH4. Thus treatment of 7,7-dibromo-bicyclor4.1.01heptane (3) with LiAlH4 in ether for 18 hr. gives the anti- and syn-monobromo derivatives (4) and (5) together with the parent hydrocarbon (6) in the... 

Extrusion of carbon dioxide to give cyclopropyl ketones has been observed in the treatment of 2-acylbutanolides with a halide salt in DM SO or DMF (equation 8). 4-Aryl-or 4-alkenylbutenolides also expel CO2 photochemically. Irradiation of cyclobuta-nones with UV light often gives cyclopropanes by loss of carbon monoxide . In this... 

Reactions of phenylthiocyclopropyl lithium with alkyl halides and epoxides have also been reported to deliver products opened to a variety of carbonyl derivatives jS-(l-Phenylthio)cyclopropyl enones have been prepared by using lithium salts of a-hydroxymethylene ketones as electrophiles and dehydrating with acid (equation 110). Rearrangement to cyclobutanones occurs with trifluoroacetic acid, whereas thermal vinylcyclopropane-cyclopentene expansion sometimes gives mixtures of regioisomers . 

The reduction of tertiary cyclopropyl halides with alkali metal naphthalenides leads to a similar situation. After treatment of a 78 22 and a 25 75 mixture, respectively, of r-1-bromo-l-methyl-c-2-methyl-r-2-phenylcyclopropane (110) and its isomer (111) with LiN in THE at 20°C, protonation with methanol led to identical 45 55 mixtures of r-l-phenyl-l,c-2-dimethyl- and r-1-phenyl-l,r-2-dimethylcyclopropanes (112 and 113). 

Thus, the results in solution with the cyclopropyl halides mentioned lead to the following conclusions ... 

Table 18 summarizes the net retentions of configuration of the cyclopropane 49 observed in the reactions of the optically active cyclopropyl halides 5(1-52 with alkali metal naphthalenides MN as the halide X, the gegenion M and the concentrations are varied. The effect of inverse versus normal addition is demonstrated in Table 19. The influence of the solvent is given in Table 20. Dicyclohexyl-18-crown-6 also affects the. amount of retention of cyclopropane 49 (Table 21).

What is the reason for the alternative pathways in the reactions of the cyclopropyl halides 106,107,110, 111, 114 Hal, 115-Haland 50-1,51-Br, 52-CI, 118-Hal with alkali metal naphthalenides ... 

Undoubtedly, in the case of the cyclopropyl halides 106, 107, 110, 111, 114-Hal and 115-Hal the normal mechanism with the cyclopropyl radical participating in the productdetermining step is observed. The cyclopropyl halides 5(1-52 and 118-Hal, however, seem to react in such a way that cyclopropyl halide radical anions CprX M anri or cyclopropyl radical complexes Cpr X M" are kinetically significant. The question whether species of this type indeed exist is an important issue ... 

Symons critically discussed the results of Garst and coworkers. He points out that although it is very unlikely that an ion paired halide radical anion R-X exists in the case of R = 5-hexenyl, R X complexes possessing weak residual charge-transfer interactions would also be expected to differ kinetically from each other as the halide is varied. Of special significance for the interpretation of the results obtained with the cyclopropyl halides 50-52 and 118-Hal are the following conclusions of Symons ... 

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