O. M. NEFEDOV, N. N. NOVITSKAYA, and Corresponding Member of the Academy of Sciences of the USSR A. D. PETROV

PREPARATION OF CYCLOPROPANE HYDROCARBONS BY REDUCTION OF ADDUCTS OF DIHALOCARBENES TO OLEFINS

It is known \((^{1})\) that dihalocarbenes, and especially dichlorocarbene, are the most accessible of the carbenes. At the same time, \(\mathrm{CCl_2}\) and \(\mathrm{CBr_2}\) possess very high reactivity and, simultaneously (in contrast, for example, to \(\mathrm{CH_2}\)), selectivity in electrophilic addition reactions to multiple bonds \((^{2})\). Consequently, provided the latter are sufficiently nucleophilic, the corresponding gem-dihalocyclopropane (or cyclopropene) compounds are essentially the sole reaction products (under optimum conditions the yields are 70–90% of theory) \((^{3-5})\). However, effective general methods for reducing these gem-dihalo derivatives to hydrocarbons of the cyclopropane series had not yet been found. Attempts at reduction, for example, of 7,7-dichloronorcarane (I) with hydrogen at the moment of its liberation (abs. \(\mathrm{C_2H_5OH + Na}\)) at \(\sim 80^\circ\) \((^{6})\), or with molecular hydrogen over Raney Ni at \(\sim 20^\circ\) in the presence of \(\mathrm{C_2H_5ONa}\) \((^{6})\), or KOH \((^{7})\), proved unsuccessful. Under these conditions reduction of I either did not occur at all, or was accompanied by hydrogenolysis of the cyclopropane ring with formation of methylcyclohexane (yield 30–40%). Somewhat more readily, but likewise quite incompletely and nonselectively, 7,7-dibromonorcarane was reduced under similar conditions (aq. \(\mathrm{CH_3OH + Na}\))—the yield of norcarane was \(\sim 20\%\) of theory \((^{7})\). Only 1-phenyl-7,7-dibromonorcarane and 1-phenyl-2,2-dichlorocyclopropane could be converted by the action of sodium in alcohol, in yields of 70–80%, respectively into 1-phenylnorcarane \((^{6})\) and phenylcyclopropane \((^{5})\). Good results were also obtained in the reduction of tetrachlorobicyclopropyl with excess lithium and tert.-\(\mathrm{C_4H_9OH}\) in diglyme \((^{8})\), and of gem-dibromotetramethylcyclopropane with tri-n-butyltin hydride in pentane \((^{9})\). However, both of these methods required considerable time (up to 3 days and more) and, moreover, had been tested only on isolated examples.

Continuing the search for optimum conditions for converting gem-dihalocyclopropane compounds into hydrocarbons of the cyclopropane (norcarane) series, in the present study we investigated the reduction, by various methods, of 7,7-dichloronorcarane (I) and a number of other gem-dihalocyclopropane compounds obtained in 80–90% yields by addition of dihalocarbenes (from \(\mathrm{HCX_3}\) and tert.-\(\mathrm{C_4H_9OK}\)) to olefins:

\[ \begin{array}{c} \begin{array}{ccc} & & \\ \end{array} \end{array} \qquad \begin{aligned} &\text{olefin} + :\mathrm{CX_2} \;\longrightarrow\; \text{gem-dihalocyclopropane} \;\longrightarrow\; \text{cyclopropane hydrocarbon}, \end{aligned} \qquad \text{where } X=\mathrm{Cl}\ \text{or}\ \mathrm{Br}. \]

Initially undertaken attempts to reduce I with an excess of \(\mathrm{LiAlH_4}\) in ether in the temperature range from \(-65\) to \(+40^\circ\) (7 hr) proved fruitless (conversion of I not more than 5%), although under similar conditions di- and polychloromethanes, as is known \((^{10})\), are converted to methane in 36–81%. The reduction of I and its 1-methyl- and 1-phenyl-substituted homologs with a 5-fold (relative to the stoichiometric ratio) excess of sodium in boiling \(\mathrm{CH_3OH}\) was also unsuccessful—the yields of the corresponding norcaranes amounted to 1–7% of theory. Increasing the sodium excess to 10-fold (3–9 hr boiling in \(\mathrm{CH_3OH}\) or \(\mathrm{C_2H_5OH}\)) makes it possible to increase the conver-

of the initial I (up to 70–75%). However, the content of norcarane in the reduction products in this case does not exceed 50–60%. In contrast to the dichlorides, 7,7-dibromonorcarane was reduced with a 5- to 6-fold excess of sodium in methanol even at −40 to −50° (conversion ∼50%), but the products formed also contained considerable amounts of methylcyclohexane. It is interesting to note that, in the reduction of I with sodium in 95% \( \mathrm{C_2H_5OH} \) or with lithium aluminum hydride in boiling \( (\mathrm{C_2H_5})_2\mathrm{O} \), along with hydrocarbons there is formed 7-chloronorcarane—the product of incomplete reduction of the starting dichloride (yield 2–3%). This apparently indicates the stepwise character of the reduction of gem-dihalocyclopropanes, which is consistent with the data of \((^9)\).

In further selecting conditions for the reduction of gem-dihalides of the cyclopropane series, we decided to use for this purpose a solution of sodium in liquid ammonia. With this reagent, G. and L. Closs \((^{11})\) have recently successfully carried out the reduction to cyclopropanes (yields 82–87%) of a series of their monochloro derivatives, formed in 25–50% yields by the reaction of \(\mathrm{CHCl}\) (from \(\mathrm{CH_2Cl_2}\) and AlkLi) with olefins. These same conditions (a solution of a 1.1–2.5-fold excess, relative to stoichiometry, of Na in \(\mathrm{NH_3}\), temperature from −60 to −70°) proved optimal also for the reduction to cyclopropanes of various gem-dichloro- and dibromocyclopropanes (norcaranes). As is evident from the data of Table 1, the conversion of these dihalides into hydrocarbons

Table 1

\(^{1}\) According to \((^{13})\), b.p. 116.5°, \(n_D^{25}\) 1.4546.
\(^{2}\) Yield from 7,7-dibromonorcarane 87% of theory.
\(^{3}\) Yield from 1-methyl-7,7-dibromonorcarane 86% of theory.
\(^{4}\) According to \((^9)\), b.p. 82° (2.5 mm), \(n_D^{20}\) 1.5400, \(d_4^{20}\) 0.9751.
\(^{5}\) Literature data \((^{12})\): b.p. 91.4–91.5° (52 mm), \(n_D^{20}\) 1.5337, \(d_4^{20}\) 0.9415.
\(^{6}\) According to \((^1)\): b.p. 128–129°, \(n_D^{25}\) 1.4105.

is usually 85–95%, with a cyclopropane content in the latter of 94–100%. Thus, in the case of norcaranes the yields of the readily separable products of hydrogenolysis of the three-membered ring do not exceed 4–6%, while in the case of alkyl-substituted cyclopropanes hydrogenolysis is altogether absent. In particular, in experiments on the reduction of the dichlorocarbene adducts to heptenes-1 and -2 we were unable to detect even traces of possible hydrogenolysis products (\(n\)-octane, 2- and 3-methylheptanes) or any other impurities. Only 1-phenyl-2,2-dichlorocyclopropane formed under these conditions, along with phenylcyclopropane (yield ∼50%), a considerable amount (up to 17%) of \(n\)-propylbenzene, with the complete absence, as well as

as was to be expected \({}^{(12)}\), from isopropylbenzene:

\[ \mathrm{C_6H_5{-}CH(-CCl_2){-}CH_2} \ \xrightarrow[\ -60\div -70^\circ\ ]{\mathrm{Na+NH_3}}\ \mathrm{C_6H_5{-}CH{-}CH_2} \begin{array}{c} \!\!\!\!\!\!\!\!\!\!\diagup\!\!\!\!\!\!\!\!\!\!\diagdown\\[-6pt] \mathrm{CH_2} \end{array} +\mathrm{C_6H_5(CH_2)_2CH_3}. \]

In addition, when a large, for example 2–3-fold, excess of sodium was used, here, as in the case of other aryldihalocyclopropanes and especially naphthyldichloronorcarane (see Table 1), partial hydrogenation of the aromatic ring also occurred.

The reaction of reduction of dihalocyclopropanes with a solution of sodium in ammonia, like the reaction of addition of dihalocarbenes to olefins \({}^{(1-3)}\), has a stereospecific character, which was shown by us on the example of the formation and reduction of the adduct of \(\mathrm{CCl_2}\) to heptene-2.

Thus, the proposed method for obtaining cyclopropane hydrocarbons from olefins via their adducts with dihalocarbenes is very universal, simple, and not time-consuming. Moreover, it is based on extremely accessible reagents and at the same time makes it possible, in high overall yields (65–85% of theory in total over both stages), to obtain very pure cyclopropanes. It should be noted that direct methylenation of olefins with \(\mathrm{CH_2I_2}\) and the zinc–copper couple according to Simmons and Smith \({}^{(13)}\) gives considerably lower yields of cyclopropane hydrocarbons (on average 30–50%) with experiment durations of 48–72 hours.

The structures of the cyclopropane (norcarane) hydrocarbons obtained as a result of the present investigation (for properties see Table 1) were proved by means of NMR and IR spectra and gas–liquid chromatography. In particular, in the proton-resonance spectra of these hydrocarbons, recorded by A. S. Khachaturov on a JNM-3 spectrometer, there are distinct signals of the protons of the trimethylene ring in the region 9.0–9.5 m.d., and there are no signals of protons at a multiple \(\mathrm{C{=}C}\) bond (in the region 3.5–7 m.d.). The absence of \(\mathrm{C{=}C}\) bonds is also indicated by the data of the IR spectra, which were recorded by G. K. Gaivoronskaya on an ISP-51 spectrometer.

Experimental Part

The starting 7,7-dichloronorcaranes were obtained in 70–90% yields by addition of dichlorocarbene, formed from \(\mathrm{HCCl_3}\) under the action of tert-\(\mathrm{C_4H_9OK}\), to the corresponding cyclohexenes (molar ratio \(1:1:2—4\)) at \(-10\div -15^\circ\), and had properties coinciding with those reported earlier \({}^{(4)}\). Similarly, from styrene was prepared 1-phenyl-2,2-dichlorocyclopropane, yield 84%, b.p. \(113^\circ\) (16 mm), \(n_D^{20}\) 1.5522, \(d_4^{20}\) 1.2290 (according to \({}^{(5)}\), b.p. \(114^\circ\) (13 mm), \(n_D^{23}\) 1.5501); from heptene-1 was obtained 1-\(n\)-amyl-2,2-dichlorocyclopropane, yield 69%, b.p. \(76^\circ\) (15 mm), \(n_D^{20}\) 1.4541, \(d_4^{20}\) 1.0360.

\[ \begin{array}{rlrrrrrr} \mathrm{C_8H_{14}Cl_2}. & \text{Found, \%:} & \mathrm{C} & 53.20; & 53.09; & \mathrm{H} & 7.99; & 8.05; & \mathrm{Cl} & 39.11; & 38.99\\ & \text{Calculated, \%:} & \mathrm{C} & 53.02; & & \mathrm{H} & 7.80; & & \mathrm{Cl} & 39.18 \end{array} \]

And from heptene-2 (isomer ratio \(1:5\))—1-methyl-2-\(n\)-butyl-3,3-dichlorocyclopropane of exactly the same isomeric composition, yield 83%, b.p. \(74^\circ\) (15 mm), \(n_D^{20}\) 1.4565, \(d_4^{20}\) 1.0428.

\[ \begin{array}{rlrrrrrr} \mathrm{C_8H_{14}Cl_2}. & \text{Found, \%:} & \mathrm{C} & 53.40; & 53.34; & \mathrm{H} & 8.04; & 8.14; & \mathrm{Cl} & 39.01; & 38.88\\ & \text{Calculated, \%:} & \mathrm{C} & 53.02; & & \mathrm{H} & 7.80; & & \mathrm{Cl} & 39.18 \end{array} \]

Under the same conditions, replacing \(\mathrm{HCCl_3}\) by bromoform, 7,7-dibromonorcarane was obtained from cyclohexene, yield 75%, b.p. \(113–114^\circ\) (17 mm), \(n_D^{20}\) 1.5581, \(d_4^{20}\) 1.7835 (according to data \({}^{(7)}\), b.p. \(100^\circ\) (8 mm), \(n_D^{22}\) 1.5578), and from 1-methylcyclohexene—1-methyl-7,7-dibromonorcarane, yield 79%, b.p. \(68–69^\circ\) (2 mm), \(n_D^{20}\) 1.5520, \(d_4^{20}\) 1.6875.

\[ \begin{array}{rlrrrrrr} \mathrm{C_8H_{12}Br_2}. & \text{Found, \%:} & \mathrm{C} & 36.01; & 36.00; & \mathrm{H} & 4.65; & 4.59; & \mathrm{Br} & 59.76; & 59.65\\ & \text{Calculated, \%:} & \mathrm{C} & 35.85; & & \mathrm{H} & 4.51; & & \mathrm{Br} & 59.64 \end{array} \]

Reduction. To a solution, cooled to \(-60\) to \(-70^\circ\), of 6–12 g (0.25–0.5 g-at.) of sodium in 200–250 ml of liquid \(NH_3\), 0.1 mole of gem-dihalocyclopropane in 50–100 ml of anhydrous ether was added over 15–20 min. The mixture was stirred at the same temperature for 0.5–3 hr, after which 13.5–27 g (0.25–0.5 mole) of \(NH_4Cl\) was added and the excess \(NH_3\) was evaporated. A little water was added to the residue, the organic layer was separated, and, after the usual work-up, distilled on a column. Analysis of the reduction products, as well as monitoring of the purity of the starting and final substances, was carried out by chromatography on a gas–liquid chromatograph with a thermal-conductivity detector (3–4 m columns with 10% triethylene glycol butyrate or 15% tricresyl phosphate on diatomaceous brick; carrier gas—He). The results of the reductions and the properties of the cyclopropane hydrocarbons thus obtained are given in Table 1.

In the reduction of aryldihalocyclopropanes it is desirable to reduce the excess of sodium to 5–15% of the stoichiometric amount.

We express our gratitude to I. L. Safonova and O. V. Bragin for providing standard samples of cyclopropyl- and \(n\)-propylbenzenes, and to V. I. Bogomolov for assistance in carrying out the chromatographic analysis.

Institute of Organic Chemistry
named after N. D. Zelinskii
Academy of Sciences of the USSR

Received
11 VII 1963

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