Electrochemical reduction of 1,3-diketones in hydroorganic medium. Preparation of 1,2-cyclopropanediols

JOSEPH ARMAND AND LINE BOULARES Laboratoire de Pl~ysicochirnie des Solrltiot~s, UtliversitP Paris VI, 8, Rue Cuvier 75230 Paris CPdex 05, France

Received July 21, 1975

JOSEPH ARMAND and LINE BOULARES. Can. J. Chem. 54, 1197 (1976). The electrochemical reduction of 1,3-diketones C6H5-CO-CRIR2-CO-R3 (R1 = H,

CH3; RZ = CH3, CH2C6H5; R3 = CH3, C6H5) in an hydroorganic medium corresponds to a bielectronic process and leads to I,?-cyclopropanediols which, in most cases, are obtained in good yields. The polarographic results are presented and the mechanisms are discussed,

JOSEPH ARMAND et LINE BOULARES. Can. J. Chem. 54, 1197 (1976). La r6duction 6lectrochimique des dicetones-1,3, C6H5-CO-CRIR2-CO-R3 (R1 = H,

CH3; R2 = CH,, CH2C6H5 ; et R3 = CH,, C6H5), dans un milieu hydroorganique correspond k' un processus bi6Lectronique et conduit aux cyclopropanediols-l,2 qui sont obtenus dans la plupart des cas avec de bons rendements. On prisente les risultats polarographiques et on discute des micanismes.

[Traduit par le journal]

Introduction

In a preceeding paper (I), we described the polarographic behaviour of 1,3-diphenyl-1,3- propanediones with a n halogeno, acetoxy, or amino group on the 2-position. This led us to investigate the electrochemical reduction in hydroorganic medium of p-diketones such as RICOC(R2)(R3)COR4 (R,, R2, R3, R4 = alkyl or aryl).

Polarography and electrolysis of 1,3-diphenyl-1,3- propanediones and 1-phenyl-1,3-butanediones

2,2- Ditnetlzyl-1,3-cIi~~he11yl-l,3-~~ro~~aneclione, 3. and 2-Methyl-1,3-cliplzenyl-l,3-l~ropa1ze- cliorze, 2

The electrochemical reduction of 1 has been reported in several papers (2-5). In a water- ethanol medium the polarograms of 1 show one, two, or three waves according to the p H (4). The first monoelectronic wave corresponds to the dimerization in eq. 1, while the second wave is

assigned to the reduction of the dimer 1' into a cyclic tetrol, as in eq. 2. In solution, compound 1

is in an enolic form lE (6) and most probably it is this enolic species which is reduced at the electrode, as the formation of 1' by preparative electrolysis shows that the behaviour of 1 is analogous to that of benzalacetophenone C6H~CH=CH-CO-C6H5 (2).

As unenolizable 1,3-diphenyl-1,3-propanedi- ones had never been investigated, we became interested in the behaviour of 2,2-dimethyl-1,3- diphenyl-l,3-propanediones, 3.1

In the p H range where it is stable ( p H 1-10) 3 presents a 2e cathodic wave (by reference to benzil a t p H 1); this wave is distorted a t p H higher than 4.5; its E,,, varies with the p H as shown in Fig. 1. Electrolysis in dilute solu- tions (C = M, CH30H 50%) consumes about 2 electrons per molecule a t p H 3.7 ( E =

'In DMSO, it was shown that the electrochemical reduction of 3 gives a radical anion which slowly de- composes into several products amongst which is isobu- tyrophenone (8).

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CAN. 1. CHEM. VOL. 54. 1976

-0.9 - as .IJI -ID -10 -10 -1.1 -1.2 -1.3

FIG. 1. Polarograms of 3, GH5-CO-C(CH3)2-CO-C& ( C H 3 0 H 50:';, C = lo-' M).

- 1.25 V) as well as at pH 7.15 (E = - 1.50 V); [41 C ~ H S - C O - C H ( C H I ) - C O - C ~ H ~ + 2e- + 2Hf

the electrolyzed solutions show a 2e anodic wave 2

(Ell, = -0.15 V at pH 7.15). Preparative elec- C6H5 C6Hs trolysis carried out with 600 mg of 3 at pH 3.7 . gives the cis-3,3-dimethyl-l,2-diphenyl-l,2-cyclo- propanediol, 4, in 8OY0 yield. Compound 4 CH3 shows the same anodic wave which was observed 5 during the coulometries of 1. This wave tor- l-P/~enyl-l,3-butunedione utld some 2-Subsrirured responds to the oxidation of 4 into 3, and the Derivutives reduction scheme is shown in eq. 3.

The polarographic behaviour of 1-phenyl-1,3- [31 C ~ H J - C O - C ( C H ~ ) ~ - C O - C ~ H ~ + 2e- + 2 H + butanedione, 6 , has been investigated in a

3 water-ethanol medium by Zuman and co-

H:$$

6,s workers (7). Between p H 1 and 5, 6 gives a 2e

(......r. wave il; at pH higher than 5, il decreases at the expense of wave i2 with a more negative El!,; i2 in its turn is replaced by a more negative

CH3 4

wave i3. The sum of the wave heights il + i2 + i3 remains close to 2e to pH 10. In the 3-8 p H

Between pH 1 and 10 a2e wave is seen for 2which range, preparative electrolysis gives the 4- is p H dependent (Fig. 2). Coulometry at pH 3.72 hydroxy-4-phenyl-2-butanone C6H5-CHOH- (C = 2 X M, CH30H 50%, E = - 1.25 V) CH2-CO-CH3 7 with a 'good' undetermined indicates the consumption of 2e per molecule yield. Compound 7 is obtained as an oil after and the resulting solution gives a 2e anodic wave evaporation of the electrolyzed solution, etheral (Ell2 = 0.00 V at pH 3.7, Ell, = - 0.27 V at extraction, washing of the etheral solution with pH 7.0) (Fig. 3). Preparative electrolysis with 1 g a dilute sodium hydroxide solution, and evapora- of 2 at pH3.7 gives 80% of one of the three tion of ether. The purpose of washing of the isomers (one of the two meso or the dll) of 113- etheral extracts with sodium hydroxide solutions diphenyl-2-methyl-1.2-cyclopropanediol 5. Spec- is to separate 6 from 7. The authors point out tral data allow us to assign the structure of that between pH 6 and 9, during the electrolysis r-l-methyl-r-2,r-3-diphenyl-c-2,c-3-cyclopropane- of dilute solutions, an anodic wave can be diol to 5. Compound 5 shows the same anodic observed (Ell, = -0.15 V at pH6.9, E1/2 = wave which was observed in the course of dilute -0.34 V at pH9.3). On the contrary the oil electrolysis of 2: this wave is related to the isolated from preparative electrolysis does not oxidation of 5 to 2. Thus, the reduction scheme show an anodic wave. The compound responsible is as described in eq. 4. for the anodic wave is ignored in the discussion;

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-0.7 ' - 0 6 -0.9 -0.9 -1.0 -10 -1.0 -11 -1.3

I FIG. 2. Polarograrns of 2, C6H5-CO-CH(CH,)-CO-C6H5 (CH30H 50%, C = lo-' M).

the three waves il, i2, and i3 are all assigned to the overall reduction scheme in eq. 5. The

1 [5] C6H5COCH2COCH3 + 2e- + 2H+ +

I C6H5CHOHCH2COCH3

reduced species are different for the three waves: il corresponds to the reduction of a biprotonated form, iZ to that of a monoprotonated form, and i3 to the reduction of the neutral n~olecule. Without detailing their arguments further, the authors state that the diketo form is reduced and not the en01 form. The enolic tautomer, which accounts for about 40% of the product in the medium used, would be transformed into diketone as this last species is reduced. This last point seems quite plausible because, as we have

FIG. 3. Electrolysis of C6H5-CO-CH(CH3)--CO- I C6H5, 2 (pH = 3.72, 50% CH30H, C = 2 X M , I

V = 200 ml, E = - 1.25 V) (a) before electrolysis, (6) at the end of the electrolysis.

already seen in the case of 1, if the enolic form was reduced, 6 should behave as benzalaceto- phenone C6H5 CH=CHCOCH3. Benzalaceto- phenone (2) is known to show a one electron wave leading to the reduction into an e-diketone (eq. 6). The presence of an anodic wave during

the electrolysis of dilute solutions of 6 in addi- tion to the preceding results ( I ) suggest at least a partial yield of a 1,2-cyclopropanediol. There- fore the investigation of compounds of the type C6H5-CO-C(RI)(R2&CO-CH3 was under- taken.

I-Phenyl-1,3-butarzedione 6 Electrolysis of dilute solutions of 6 were per-

formed to measure the height of the anodic wave described by ref. 7. These electrolyses were carried out under argon: (a) at p H 3.80 (C =

2 X M, CH30H 20%, E = - 1.25 V), an anodic wave is observed at the end of the elec- trolysis = -0.10 V) and its height reaches about 20% of the initial wave of 6; (b) at pH 7.23 (C = 2 X lop3 M, CH30H 50%, E = - 1.60 V) the anodic wave = - 0.08 V) reaches about 30% of the sum of the waves il + i2 + i3 of 6; (c) at pH6.58 (C = 2 X lop3 M, CH3OH 20%, E = - 1.60 V) the height of the anodic wave (El/, = -0.05 V) is about 50% of the total height of waves il + i2 of 6 (Fig. 4). The uv spectrum at completion of the electrolysis

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1200 CAN. J. CHEM. VOL. 54. 1976

FIG. 4. Electrolysis of CsHS-CO-CH2-CO-CH3, 6 ( p H = 6.58, 20th CH30H, C = 2 X 10-3 M, V = 200 ml, E = - 1.60 V) (a) before electrolysis, (b) end of the electrolysis.

shows the complete disappearance of the absorp- tion of the C6H5CO- and C6H5--C(OH)= CH- groups. As in the case of ref. 7, 2e are consumed per nlolecule in our electrolysis. The results obtained in addition to those discussed above suggest a yield of about 50% of 12 - cyclopropanediol in dilute solutions at pH 6.58. Thus, cyclopropanediol is not isolated from preparative electrolysis either because it is oxi- dized into 6 and washed away with sodium hydroxide or because it is transformed during the treatment of the etheral extracts with sodium hydroxide and eliminated with the aqueous layer (a transformation cyclopropanediol 4 C6H5- CHOHCH2COCH3 does not seem very likely).

l-Phenyl-2-methyl-l,3-butanedione, 8 Between pH 1 and 8, compound 8, C6H5-

CO-CH(CH3)-CO-CH3, shows a pH de- pendent 2e wave (C = M, 50y0 CH30H).

Coulometry at pH7.4 (C = 2 X lop3 M, CH30H 507'(',, E = - 1.50 V) consumes about 2e per mol and at the end, the solution presents an anodic wave (El/, = -0.12 V) the height of which is about 75y0 of that of the wave of 8. At pH 3.74 electrolysis in dilute solution (C = 2 X lop3 M, CH30H 50y0, E = - 1.30 V) also gives a com- pound with an anodic wave. By changing the pH of the electrolyzed solution from 3.74 to 7.4

an anodic wave is observed (El l2 = -0.12 V); its height is about 70% of the height of the wave of 8 at pH 7.4.

I-Phenyl-2,2-dirnethyl-l,3-butatledione, 9 Between pH 1 and 8 C6H5-CO-C(CH3)2-

CO-CH3, 9, presents a pH dependent 2e wave (C = M, 50% CH30H). Coulometry at

pH7.95 (C = 2 X lop3 M, CH30H 50%, E =

- 1.55 V) consumes 2e per In01 and the elec- trolyzed solution shows an anodic wave =

-0.08 V), the height of which is about 65y0 of the height of the wave of 9. At pH 3.82 electrolysis (C = 2 x lo-3 M, C,H 3 0 H 5070, E = - 1.25 V) also gives a compound with an anodic wave: by changing the pH to 7.9 an anodic wave with El/, = -0.08 V is observed, the height of which is about 60% of the height of the wave of 9. Preparative electrolysis carried out with 1 g at pH3.7 gives SOYO of a 50:50 mixture of the two isomers of 1,1,2-trin1ethyl-3-phenyl-2,3-cyclo- propanediol, 10 [7].

CHI I

[71 C&-CO-C-CO-CHI + 2e- + 2 ~ + I

CHI

C ~ H S 5H3

C H ~ 10

1 - Phenyl-2-benzyl-2-~hyl-1,3-butanedione, 11 At pH3.7, 9 gives a 2e wave with ElI2 =

- 1.16 V. Electrolysis in dilute solution at this pH (C = 1.5 X lop3 M, CH30H 5070, E =

- 1.30V) consumes 2e per mol and the resulting solution shows an anodic wave (Ell2 = -0.05 V at pH7) the height of which is, at pH = 7. about 30y0 of the height of the wave of 11. Preparative electrolysis carried out at pH 3.7 with 400 mg of 11 gives an oil. The nmr spectrum and the easy oxidation into 11 indicate a mixture of the isoluers of 1,3-dimethyl-2-phenyl-3-benzyl- 1,2-cyclopropanediol 12 [8].

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I [8] C6H5-CO-C-CO-CH3 + 2e- + 2 ~ '

[I21 ( - 3 - 7 3 Electrochemical reduction I CH3 THF, Ac20,

C H ~ C ~ H S 0 Nf Bu3EtBF4-

H

"f cH2cbH5 c 3 Electrochemical reduction - 12 THF, A c ~ O , NfBu3EtBF4-

0 Discussion: Reduction Mechanism

Besides the 8-diketones already mentioned, some cyclic 8-diketones have been investigated by electrochemistry. Thus, 2-phenyl-1,3-indane- dione is reduced in hydroorganic medium according to ref. 19 as in eq. 9. The scheme shows

0 I I r HP 1

that this compound behaves as an a-diketone (reduction into an enediol followed by a re- arrangement into an a-ketol). This is not sur- prising as this compound is a vinylogue of a-diketone. In alcoholic medium the schemes shown in eqs. 10 and 11 were demonstrated (20).

H,cc*,

AcO H3C CH3

behaves as an a-ethylenic ketone; the reduction is monoelectronic and gives an e-diketone. When the diketo form is reduced the reduction pro- ceeds, a t least partially, as a simple ketone; a 8-ketol (19, 20) and a pinacol (20) can be isolated. Our results show that 1,2-cyclopropane- diols are obtained in some cases.

Derivatives 2, 3, 9 and 11 do not give alcohol or pinacol; if they had been formed they would have been isolated together with the 1,2-cyclo- propanediol and detected by nmr. In the case of 6, the results of Zuman (7), as well as our own, indicate the simultaneous formation of 1,2-cyclopropanediol and of alcohol.

In an acidic or a neutral protic medium, the overall first step of the reduction mechanism for the compounds investigated is shown in eq. 14.

Two routes are then possible as shown in eqs. 15 and 16. Reaction 15 could be operative when RJ = C6H5 as the group -C-C6H5 is electro-

I I In aprotic medium, the first derivatives of 0

1,2-cyclopropanediols were obtained by electro- reducible but not in the case when R3 = CH3 as chemical reduction (9) as illustrated in eqs. 12 the aliphatic ketones are not electroreducible in and 13. In protic medium the results described hydroorganic medium. Reaction 16 seems more in the literature show that when the 8-diketone likely as it explains the formation of both the is enolizable and when it is reduced as an en01 it alcohol and the 1,2-cyclopropanediol; this last

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1202 CAN. J . CHEM. VOL. 54. 1976

compound would be obtained through a nucleo- philic attack of the carbanion on the P-carbonyl group. The alcohol-cyclopropanediol ratio de- pends on the relative values of reaction rates kl and k2 which, in turn, depend on the nature of R1, R2, and R3.

Conclusion

It is shown that in hydroorganic medium the I

P-diketones such as C~HS-CO-C-CO- show

a 2e polarographic wave which c&responds to a reduction t o a 1,2-cyclopropanediol. Previous t o this investigation, three 1,2-cyclopropanediols had been synthesized: Rausch and Priddy (10) had reduced cyclic p-diketones by alkaline metals in liquid ammonia; these same authors and, simultaneously, Curphey and McCartney (11, 12) had shown that the 1,2-cyclopropanediols were the expected intermediates in the Clem- mensen reduction of p-diketones; finally a cyclo- propanediol was obtained by reduction of a P-diester by sodium in liquid ammonia (13).

The method used in this paper, the electro- chemical reduction in hydroorganic medium, yields cyclopropanediols easily and in fair yields. Thus, it complements the other methods which can be used in a limited number of cases only.

Experimental The techniques and apparatus used have already been

described (14). All the potentials are given by reference to the saturated calomel electrode.

Preparation of Comporrtzds 2, 3, 7, 8, 9, a t ~ d 11 C6H5-CO-C(CH3)2-CO-C6H5, 3, is prepared by a

Friedel-Crafts reaction between the dichloride of 2,2- dimethyl malonic acid and benzene according to ref 15; (CH3)2C(COC1)2 is obtained by reaction of SOC12 with malonic acid according to ref. 16; mp = 96 "C. C17H1602 nmr (CDCI,): 6 protons, CH3 s at 1.67 ppm; 10 protons, C6H5, centered at 7.4 and 7.8 ppm; uv (CH3OH): 248 nm ( E 18 200), 280 nm (e 2200).

The preparation of C6H5-CO-CH(CH3)-CO- C6H5, 2, and its physicochemical properties have been described in a recent paper (1).

C6HS--CO-CH2-CO-CH3 is an analytical E.G.A. product.

C6HS-CO-CH(CH3)-CO-CH3 is prepared by the reaction of the sodium salt of 6 with CH31 according to ref. 17; bp 13C-134 "C/11 torr CI IHIZO~ nmr (CDC13):

I (a) diketone: 2.7 protons, CH,-CH-, d at 1.43 ppm;

I

0.9 protons, CH3-C-H, q at 4.56 ppm, Jcm;-cH = 7

I Hz; 3 protons, CH3-CO, s at 2.17 ppm; 5 protons, C6HS, m centered at 7.7 and 8.1 ppm; (b) en01 : 0.1 protons, -C=-C-CO, s at 16.63 ppm, disappears on the

I I HO CH,

addition of DzO; 0.3 protons, -C=C-CO-, s at 1.9 I I

ppm. This spectrum shows that the en01 accounts for about 10(yo of the product. Ultraviolet (CH30H): 246 nm ( E 10 800), 285 nm ( E 1700).

C6HS-CO-C(CH3)2-CO-CH3, 9, is prepared by the reaction of the sodium salt of C6HS-CO-CH(CH3) -CO-CH3, 8, with CH31 according to ref. 6; bp 84 "C/2 torr. Cl2Hl4O2 nmr (CDCI3): 6 protons, -C(CIf3)2-, sa t 1.47 ppm; 3 protons, -CO-CH3, s at 2.08 ppm; 5 protons, C6HS m 7.35-7.90 ppm; uv (CH30H): 243 nm ( e 9600), 275 nm ( e 1200). C6HS-CO-C(CH3XCH2C6H5)-CO-CH,, 11, is pre-

pared by reaction of the sodium salt of 8 with C6HSCH2Br according to ref. 18; mp 105-106°C. ClsHlaOz nmr (CDCI,): 3 protons, -CO-C(CH3)-CO, s at 1.37 ppm; 3 protons, -CO-CH3, s at 2.10 ppm; 2 protons, -C(CH2--C6H5)-CO-, d at 3.44 ppm; 10 protons, -C6HSr m at 6.85-8.05 ppm.

Prepararive Elecrrolysis Electrolysis of 3, C6HS-CO-C(CH3)2-CO-C6H5:

250 ml of solution are prepared from 125 ml of methanol, 75 ml of a 0.5 M solution of citric acid, 30 ml of a 0.5 M solution of Na2HP04, and water. 200 ml of thls solution and 600 mg of 3 are used to fill the cathodic compartment while the remainder is used in the anodic compartment; p H = 3.70, E = -1.25 V . After consumption of 500 C

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(2e per rnol corresponds to 460 C), the current drops to 2 mA and the solution is filtered and poured into 200 ml of deoxygenated water. The aqueous solution is extracted with 2 X 100 ml of ether; the etheral extracts are dried over Na2S04 and evaporated to give an oil which crystal- lizes into a white solid, 4 ; 480 mg, SO',& yield, mp 132 "C. C17H1802: rnol. wt. 254 by mass spectrometry at 10 eV and 235 by cryometry in C6H6; nmr (CDCI]): 3 protons, -CH3(a), s at 1.07 ppm; 3 protons, -CH3(h), s at 1.37 ppm; 2 protons, --OH, s a t 3.27 ppm which disappear on the addition of D 2 0 ; 10 protons, -C6H5, s at 7.25 ppm. After a few days in the CDCI] solution 4 is reoxidized by air into 3. Ultraviolet (CH30H) shoulder around 235 nm (e 7000). On the basis of these data the formula illustrated is assigned to 4. Indeed, 4 is obtained from 3 by a reduc-

tion involving 2 electrons per molecule and 4 can be entirely reoxidized to 3. The nmr spectrum gives evidence of two nonequivalent -CHI groups. The uv spectrum shows the disappearance of the C6H5C0 group (absence of a strong band at 250 nm) and the absence of conjuga- tion with -C6H5. This assignment also relies on the results published by Reusch and Priddy (10): by reduction (Li + NH]) of a cyclic B-diketone they isolated a 1,2- cyclopropanediol which is easily reoxidized into a 0- diketone. The compound which is obtained is the pure cis derivative, as in nmr the methyl groups give two singlets of three protons each.

Electrolysis of 2, C6H5-CO-CH(CH3)-CO-C6H5 A solution is prepared as in the case of 3. Compound

2 ( 1 g) is reduced in 200 rnl of this solution; pH = 3.70 at E = -1.25 V. After consumption of 750 C (2e per rnol correspond to 800 C) the current decreases to 1 m4 . The solution is worked up as in the case of 3 to give a white solid which is dried over P2O5 and washed with de- oxygenated CCI,. A yield of 800 mg of 5 is obtained (80%); mp 122 "C (dec.). C16H1602 mol. wt. 240 by mass spectrometry at 10 eV and 220 by cryometry in benzene; imr ( cDc~~) : 3 protons, -CH-CH], d -at 1.26 ppm; 1 proton, -CH-CHI, q at 2.03 pprn, Jc.11-(.211 = 6.5 Hz; 2 protons, -OH, s at 3.17 pprn which disappears on the addition of D 2 0 ; 10 protons, -C6H5, s at 7.1 pprn; uv (CH3OH): shoulder around 230 nm (E 8000). These results agree with the formula of one of the three isomers of 1,2-diphenyl-3-metl~yl-1,2-cyclopropanediol; its physi- cochemical properties are similar to those of 4. Only one of the three possible isomers is obtained (one of the two meso or the d,l) as a single quadruplet is observed for CH-CH3 and a single doublet for the methyl. In fact, this isomer is one of the two tneso isomers as these signals are not split when the nmr spectrum is recorded in the presence of the chiral complex tris[(2,2,2-trifluoro-1- hydroxyetIlylidene)3-(1-camphorato]europium. The chem- ical shift of the methyl group (6 = 1.26 ppm) is lower (A6 = -0.1 l ppm) than the chemical shift of -CH3(b) of 4 and higher (A6 = +0.19 pprn) than the chemical shift of -CH3(a) of 4. Moreover, the substitution of

methyl by H in the I,]-dimethylcyclopropane (22) leads to a decrease of the chemical shift (A6 = -0.09 ppm) of the remaining methyl: 6cHl(CDCIl) = 1.04 ppm for the l,l-dirnethylcyclopropane and 60,1(CDC1~) = 0.95 pprn for the methylcyclopropane prepared according to ref. 21. These results lead to the conclusion that the methyl of 5 has the same position as the CHl(h) of 4 ; thus 5 is the r- l-methyl-t-2,t-3-dipI~e1~yI-c-2,c-3-cyc1opropa1~ediol.

Electrolysis of C6H5-CO-C(CHl)z-CO-CH3, 9 Compound 9 (1 g) is dissolved in 200 ml of a solution

prepared as in the case of 3; pH = 3.74, E = - 1.25 V. After 950 C (i = 1 mA) (2e per rnol corresponds to 1065 C) the solution is worked up as described before to give an oil (500 mg, yield 50cj{)), the properties of which are in agreement with those of a mixture of the two isomers of 2,3,3-trimethyl- I-phenyl- l,2-cyclopropanediol (cis and tratls diols). The nmr spectrum (CDCI,): 3 protons, -CH3(u), s at 0.93 ppm, -CH3(b), (s) at 1.00 pprn; 3 protons, -CH3(c,rf), s at 1.23 ppm; 3 protons, -CH3(e), s at 1.33 ppm and -CH,(f), s at 1.55 ppm; 5 protons,

CHI ( c . 4

-C6H5, s at 7.20 and 7.28 ppm. The cl~loroformic solu- tion is entirely reoxidized by air after three days to give 9.

Electrolysis of C6HS-CO-C(CHl)(CH2C6H5)-CO- CHI, I 1

Compound 11 (420 mg) is electrolyzed in 200 ml of the usual solution; p H = 3.70, E = - 1.30 V. After 290 C (i = I mA) (2e per rnol corresponds to 310 C ) the solution is worked up as usual to glve 200 mg (48% yield) of an oil, the properties of which show that it is a mixture of the four pairs of stereoisomers of 1-methyl-2-phenyl-3-benzyl- 3-methyl-l,2-cyclopropanediol. The nmr spectrum (CDCI,): 6 protoils, -CH3, 8 s at 0.73, 0.80, 1.17, 1.23, 1.43, 1.53, 1.63, and 1.73 ppm; 4 protons, -CHI and -OH, multiplets between 2.6 and 3.2 pprn; 10 protons, -C6H5, m 7.0-7.8 ppm. The chloroform solution of the cyclopropa~lediols is reoxidized by air into 11 in 4 days.

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1204 CAN. 1. CHEM. VOL. 54. 1976

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