Cyclopropyl magnesium bromide

Chemical shifts and coupling constants have been determined in for example cyclopropyl magnesium bromide and the compounds formed with gallium, silicon, mercury, tin and lead. A complete analysis of the metal satellite spectra of tetracyclop-ropyl lead and tin and dicyclopropyl mercury has been presented ... 

Holm determined the enthalpies of formation of a collection of hydrocarbyhnagnesium bromides by reaction calorimetry with HBr in diethyl ether . He also determined the enthalpies of formation in ethereal solution of the magnesium bromide salts of 20 Bronsted acids, HB, by measuring the enthalpies of reaction of the acid with pentylmag-nesium bromide. For those species that were reported in both studies (hydrocarbyl = phenylethynyl, phenyl, methyl, cyclopropyl, cyclopentyl, cyclohexyl), the enthalpies of formation were identical. The values are listed in Tables 3 and 4. 

The experimental enthalpies of protonation and the formal enthalpies of protonation, RMgBr —RH, are fairly constant for structurally similar species (R = cycloalkyl, primary alkyl) and would be expected to be constant also for the primary cycloalkyhnethyl-magnesium bromides. For the two examples just discussed, the formal enthalpies of protonation that are calculated using the derived enthalpies of formation for the cyclopropyl-and cyclobutylmethyhnagnesium bromides are 262 and 235 kJmoU, respectively. The mean value is thus 248 kJmoU, which is very close to that expected for the formal protonation of other primary R groups. 

Methyl cyclopropyl ketone has been prepared from ethyl aceto-acetate and ethylene bromide,6 and by the action of methyl-magnesium bromide on cyclopropyl cyanide.6-7 The procedure described for its preparation from 5-chloro-2-pentanone is similar to that of Zelinsky and Dengin.8 5-Chloro-2-pentanone has been prepared by a number of methods.9 The procedure given is essentially that of Boon 10 and of Forman.11 A similar procedure has been used for the preparation of the corresponding bromo-and iodoketones.10... 

Fig. 7.24. Yields of products of reactions of magnesium with cyclopropyl bromide (Cplirl in diethyl ether iSII) at 37"C as a function of the initial concentrations of magnesium bromide ( MgBr. a) and cyclo-propyl bromide ( CpBr]n). Symbols as lor Figure 7.2.1. The curves represent the yields when MgBr, (, = 0 and are taken from Figure 7.23 MgBr n =0.18 M. MgBr ](i = 2.6 M. Reprinted lioui (iarst <-/ /. 98. Copyright IW-4. Page No. 370. with permission from Elsevier Science.

The ester Kulinkovich reaction was used to prepare a key allylic bromide 5333 in a synthesis of neolauh-malide and isolaulimalide (Scheme 5.88). The cyclopropanol 5.332 produced by the Kulinkovich reaction of ester 5.331, as its mesylate, was subjected to ring opening with magnesium bromide. This is likely to involve electrocyclic ring opening of the cyclopropyl carbocation, followed by bromide trapping. 

Since the carbon-carbon bonds in strained cyclopropane rings have large s-character, cyclopropyl bromides underwent smooth bromine-magnesium exchange by the action of lithium tributylmagnesate (equation 27)". 

More recently, the authors of the D-model investigated the reaction of bromocyclopropane 133 with magnesium [93e], using again the equations V=l4kJ3(kfD) ]v, A = (D//cJ mentioned earlier to calculate the product distribution, but substituting another composite parameter F for A and using the same values, questioned earlier for 5-hexenyl bromide, now for cyclopropyl... 

Chlorophenvl)cvclopropvl Ketone. Under a dry nitrogen atmosphere, a mixture of 1.6 g (0.066 mole) of magnesium, 7.9 g (0.066 mole) of cyclopropyl bromide, 20 mL of anhydrous diethyl ether and 60 mL of anhydrous tetrahydrofuran was heated at reflux for 2.5 hours. The stirred mixture was cooled to room temperature and a solution of 9.04 g (0.066 mole) of 4-chlorobenzonitrile in 40 mL of anhydrous tetrahydrofuran was added over one hour. After complete addition, the mixture was heated at reflux for two hours, then cooled to room temperature. A 100 mL portion of 2N hydrochloric acid was added slowly to the mixture and stirred for one hour. The mixture was extracted with three 100 mL portions of diethyl ether. The combined extracts were washed with one 25 mL portion of water, dried over anhydrous magnesium sulfate and filtered. The filtrate was concentrated under reduced pressure to give an oil which was distilled to give 3.9 g of product. The NMR was consistent with the proposed structure. 

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