TAVARES, DORSKY, AND EASTER
2434 J. Org. Chem., Vol. 36, No. 17, 1971 subjected to desulfurization with deactivated Raney nickel (two level teaspoonfuls)1b in acetone solution (100 ml) as described above. Purification of 15 through short-path distillation at 2.5 mm, bath tem erature 105O, gave analytically pure product (187 rn%& Y$~I' 2940, 2880, 1520, 1500, 1400, and 1380 cm-1; aTun 0.87 (s, CHs), 0.85 (d, J = 5 Hz, isopropyl), - _ " and 0.82 (s, CHI) ppm. Natural Valerane from I-Valeranone.-This Droduct was nrepared from natural valeranone (120 mg) essentially as descn'bed by Hikino, ~t aZ.,lf and the identity of the product, prepared in our laboratories was established by comparison of infrared and nmr spectra of material prepared in Japan.Ie
Registry No.-3, 29969-74-2; 5 , 29863-73-8; 6 , 29863-74-9; 7, 29863-75-0; 8, 29862-76-1 ; 9, 2986377-2 ; 10,29863-78-3 ; 11, 29863-79-4 ; 12, 29863-80-7 ; 12 2,4-DNP, 29863-81-8; 13, 29863-82-9; 14, 3000894-7; 14 2,4-DNP129863-83-0; 15, 29863-84-1.
Acknowledgment. -We sincerely thank Dr. H. Hikino for helping us with natural valeranone and for providing us with the copies of his infrared and nmr spectra of valerane, Professor Edward Piers for providing us with his experimental details for the preparation of 3 from 4, Dr. David H. Buss for gas chromatograms, Mr. Nelvin C. Seffel for infrared spectra, and Rlr. David B. Holland for technical assistance. The interest and encouragement of Dr. Leonard R. Axelrod are gratefully acknowledged. This investigation was supported in part by a research grant from the Southwest Foundation for Research and Education for preparing compounds of medicinal value, and Grant A-03270-12 from the Sational Institute of Arthritis and Metabolic Diseases, National Institutes of Health, Bethesda, Rfd.
Acetylation of Pinane ROBERTF. TAVARES,* JULIAN DORSICY, AND WILLIAM nf. EASTER Givaudan Corporation, Clifton, Nezv Jersey O?'Ol4 Received September 11, 1969 When pinane was treated with acetyl chloride and aluminum chloride under Friedel-Crafts conditions, an unstable product, 2-acetyl-l-chloro-4-isopropyl-l-methylcyclohexanelwas formed. This product was transformed to a mixture of acetyl-4-isopropyl-I-methylcyclohexenesby loss of HC1. The stereochemistry of the products and its bearing on the mechanism of the Kondakov reaction is discussed.
Although the chemistry of the pinenes has been extensively studied,l relatively little has been learned about the saturated hydrocarbon, pinane. The pinane molecule is quite stable and its potentially labile cyclobutane ring is resistant to most oxidizing agents and mineral acids. It reacts only slowly with hydrogen bromide at 230" . z Whereas free-radical type reactions of pinane have been r e p ~ r t e d , ~reactions -~ of pinane by ionic mechanisms have not. However, the acetylation of saturated hydrocarbons with acetyl chloride in the presence - ~ l offers a feasible of aluminum chloride is k n ~ w n ~ and route toward functionalizing pinane. We have investigated this reaction and present here the results of our work. When an ethylene dichloride solution of the complex formed between acetyl chloride and aluminum chloride was added to pinane (1)) a mixture of chloro ketones 5 was produced. The chloro ketones lost HC1 slowly on standing. Upon heating, HCl was evolved more rapidly and the product formed was the alp-unsaturated (1) (a) B.D.Sully, Chem. Ind. (London),263 (1964). (b)D.V. Banthorpe and D. Whittaker, Chem. Rev., 66, 643 (1966); Quart. Rev. Chem. Soc., 373 (1966). (0) C. Bordenoa, Amer. Perfum. Cosmet., 80, (7), 19 (1965). (2) B. T. Brooks, "The Chemistry of the Nonbenaenoid Hydrocarbons," 2nd ed, Reinhold, New York, N . Y., 1950, p 533. (3) (a) G. Bonnet, Bull. Inst. Pin., 217, 241 (1038); 1 (1939). (h) A. Gandini, G a m Chzm. Ital., 70,254 (1940), 71, 722 (1941). (4) (a) C. Fillatre and R.Lalande, Bull. SOC.Chzm. Fr., 4141 (1968); (b) G. 8. Fisher, J. S. Stinson, and I,. A. Goldblatt, J . Amer. Chem. SOC., 76, 3675 (1953). (5) E.Muller and G. Fiedler, Chem. Ber., 98, 3483 (1966). (6) G. A. Schmidt and G. 8. Fisher, J . Amer. Chem. Soc., 76, 5426 (1954). (7) G. A. Schmidt and G. S. Fisher, ibzd., 81,445 (1959). (8) C. Fillatre and R. Lalande, Bull. SOC. Chim. Fr., 1575 (1966). (9) G. A. Olah, ed., "Friedel-Crafts and Related Rertctions," Vol. I , Interscience, New York, N . Y., 1964, p 135; Vol. 111, pp 1069-1077. (10) I. Tahushi, K. Fujita, and R. Oda, Tetrahedron Lett., 4247 (1968); 5455 (1968). (11) G.Baddeley, B. G. Heaton, and J. W. Rasburn, J . Chem. Soc., 4713 (1960).
ketone 8. When submitted to glc analysis, HC1 was again lost but the products eluted were the P,y-unsaturated ketones 6 and 7 plus a small amount of 8. That the chloro ketones formed are 2-acetyl-1-chloro4-isopropyl-1-methylcyclohexanes (5) was supported by the fact that the same products were formed by adding acetyl chloride to 1-p-menthene. Also, the unsaturated ketones eluted from the glc were identical with those prepared by the acetylation of 1-p-menthene with acetic anhydride. The nmr spectra of crude and distilled fractions of the p-chloro ketone 5 revealed that it was a mixture of a t least two priiicipal isomers 5a and 5b. One isomer (which dominated the earlier fractions of the distilled crude) showed a broad multiplet at r 6.83 (ca. 12-HZ wide, >CHCOCH,), sharp singlets at r 7.52 (CH3CO) and 8.35 [>C(Cl)CH,], and a doublet at r 9.22 ( J = 6.5 Hz, -< CH'). The nmr of later fractions showed CH3 additional peaks a t r 7.30 (ca. 1 7 - H ~wide, >CHCOCH,), a sharp singlet at r 7.77 (CH,CO), and a doublet assigned to a second a t r 9.26 J = 5.5 Hz, --< CH3) CH3 isomer. The signals for the methine protons cr t o the carbonyl indicated that this proton mas equatorial in the lower boiling isomer 5a (less broad and further downfield from TRIS) and was axial in the higher boiling isomer 5b (signal at higher field and broader due to diaxial coupling).l 2 I n accord with the above, it was found that 5a deoomposed on glc to a p,y-unsaturated ketone 6 in which the acetyl group is quasiaxial while isomer 5b decomposed to a P,y-unsaturated ketone 7 in which the acetyl
(
(12) L. M. Jackman, "Application of Piuclear Magnetic Resonance Spectrosropy t o Organic Chemistry," Pergamon Press, Elmsford, N . Y., 1959 p 116.
ACETYLATION OF PINANE
J. Org. Chem., Vol. 36, No. 17, 2971
2435
SCHEME I
L
3 P-H
0
II
CH,CCI
t I I L
0
5a
[pJCH
I J
4
5b
glc,
-HCI
4
I
V
l H /
8
dCH3 COCH,
7
group is quasiequatorial plus an a$-unsaturated ketone 8. The structures of the @,-punsaturatedketones were based on the observation that the proton a to the carbonyl in isomer 6 gave an nmr signal which was only half as broad as the corresponding proton of isomer 7 indicating that the former was quasiequatorial and the latter quasiaxial. l3 Recent evidence on the ir spectra of 4-alkyl-1-methylcyclohexyl chlorides14indicates that those compounds in which the chlorine is axial have carbon-chlorine stretching bands a t 560 & 20 cm-l and those in which the chlorine is equatorial have bands at 650 f 20 cm-l. The presence of a strong band at 540 cm-l (and no evidence of any in the 650-cm-1 region) for both 5a and 5b clearly suggest that the chlorine is axial in both isomers as indicated in Scheme I. It is not surprising, therefore, that the higher boiling fractions decompose more rapidly since they are enriched in 5b which can decompose to 8 via a trans diaxial elimination. Scheme I suggests a mechanism to explain the products formed. The acetyl chloride-aluminum chloride complex can abstract a hydride ion from cis-pinane to (13) (a) F. Camps, 3. Call, and J . Psscual, J . Org. Chem., 32, 2563 (1967). (b) A possible anomaly appears in t h a t the equatorial methine proton of 6 ( T 6.94) appear8 at higher, not lower, field than the axial proton of 7 (7 6.82). This reversal could be due t o the shielding effects of the carbonyl in much the same manner as occurs in cyclohexanone. See K. M . Wellman and F. G. Bordwell, Tetrahedron Lett., 1073 (1963). (14) C. Altona, H. J. Hageman, and E. Havinga, Bel. Trau. Chim. PaysBas, 87, 353 (1968); C. Altona, Tetrahedron Lett., 2325 (1968).
produce a carbonium ion 2 which can rearrange and abstract a hydride ion to form 1-p-menthene (4). The source of the hydride ion could be 1 or some other hydrocarbon species in the m e d i ~ m . An ~ alternative mechanism involving a-pinene, formed by the loss of a proton from 2, is not likely since a-pinene produced only residue under these reaction conditions while 4 produced the p-chloro ketones 5a and 5b. That only axial chloro compounds were detected can be rationalized from either kinetic or thermodynamic considerations. A four-membered transition state such as 10a can be considered in which the oxygen sta-
10a
10b
9
bilizes the carbonium ion and requires that the chlorine attack from the least hindered side leading to 5a. Such a four-centered transition state was first proposed by Cope.ls More recently they have been considered by (15) .4.C.Cope, T. A. Liss. and D. S.Smith, J . Amer. Chem. Soc., 79,240 (1957).
2436
TAVARES, DORSKY, AND EASTER
J . Org. Chem., Vol. 36, No. 17, 1971 TABLE I
Experimental Section18 ---8nalysis
Fraction
Bp,
O C
m t , 43
n2oD
by glca--%I % S
% 6
1 40-80 63.0 1.4572 0.0 2 92 25.0 1.4764 56.6 3 97 22.0 1.4775 68.9 4 97 27.5 1.4785 64.2 27.0 1,4792 53.2 5 97 20.0 1.4802 4 1 . 3 6 107 7 107 6 . 5 1.4802 38.5 8 107 3 . 5 1.4805 35.3 Residue 101.0 a glc shows only decomposition products of 5 .
0.0 4.3 7.4 14.6 14,*5 17.3 21.3 24.3
0.0 5.6 5.9 7.2 18.8 34.0 32.9 33.1
2-Acetyl-l-chloro-4-isopropyl-l-methylcyclohexane ( 5 ) . A,To a mixture of 200 g (1.5 mol) of AlCll in 450 ml of ethylene dichloride was added 235 g (3.0 mol) of acetyl chloride while maintaining a temperature of 15". After the dark brown solution was stirred for an addilional 20 min, it was added over a 2-hr period to a solution of 276 g (2.0 mol) of pinane (90% cis) and 100 ml of ethylene dichloride at -5'. Stirring was continued for an addit,ional 1 hr at -5' and then the reaction mixture was poured onto 2.5 1. of ice and water and the layers were allowed to separate. The aqueous layer was extracted with 200 ml of ethylene dichloride. The organic layers were combined and washed twice with 200-ml portions of HCI, twice with 200-ml
TABLE I1 SPECTRAL DATA
----___
--
COCHs
____ Ir, cm-l->=0
Compd
1710 1710 1685 1715 1715
6
7 8 5a
5b
0
I
CCHs
/ A
7.81 7.88 7.77 7.82 7.77
8.34 8.40 8.13
6.83 7.30
o t h e r ~ ~as ? ' ~the initially formed species to explain acylation results which led to the vinyl ether 9 from cis decalin and to a mixture of 6-, y-, and 8-chlorocyclohexyl methyl ketones from cyclohexene. The formation of 5b could result either from epimerization of 5a or from lob. However, since both 5a and 5b are tertiary chlorides, it is not unreasonable that a process involving epimerization via chloride exchange could conceivably occur under the reaction conditions as illustrated below.
&
COCH3
-
A
4.33 4.33
8.35 8.35
-
