residual yellow oil was chromatographed on 50 g. of alumina. This led to 90 mg. of IVa, m.p. and m.m.p. 145-146’ on crystallization from petroleum ether, and 14 mg. of IIa, 1n.p. and m.1n.p. 150-152’ on crystallization from the same solvent.
[COSTRIBUTION FROM THE S O Y E S CHEXICAL
A similar reduction of 210 mg. of Ib with 837 mg. 0: hydride yielded 58 mg. of IVb, m.p. and m.m.p. 144-146 on crystallization from petroleum ether. T h e infrared and p.m.r. spectral properties of all products were identical mith those of samples described above.
LABORATORY, USIVERSITY
O F ILLISOIS, URBANA, ILL.]
Stereochemistry of the Formation and Decomposition of 1-Pyrazolines’ BY THONAS V. T ‘ m - I U K E N ? ~ AXD KENXETHL. RINEHART, JR.?~’ RECEIVED APRIL 7, 1962 Thermal decomposition of 3-carbometlioxy-cis-3,1-dimeth~l-l-pyrazoline (7) proceeds with loss of geometry t o give, in addition to unsaturated products, both 1-carbomethoxy-cis 1,2-dimethylcyclopropane (14) and l-carbomethosy-trans1,Z-dimethylcyclopropane( 13). Light-induced decomposition of the same 1-pyrazoline results in stereospecific formation ( 14), together with some methyl tiglate Formation of the in high yield of l-carbomethoxy-cis-l,2-dimethylcyclopropane latter compound arises from a formal reversal of the addition of diazomethane to an unsaturated ester. 3-Carbomethoxytrans-3,4-dimethyl-l-pyrazoline (6) behaves analogously to pyrazoline (7).
Addition of diazoniethane to double bonds acti- decompose with retention of geometry, as reported vated by a suitable electron-withdrawing group, by von Auwers and KOnig.l5 However, major followed by thermal decomposition of the resulting errors in the analytical results of von Auwers and pyrazolines, is an established route to cyclopro- Konig in other cases have been demonstrated,st9 panes,”-” although the synthetic utility of the so re-investigation of their results with presently method is hampered by extensive formation of un- available analytical tools probably is advisable. saturated compounds in the pyrolysis ~ t e p . ~ - l ~Stereochemistry of 1-Pyrazoline Formation.von Xuwers and Konig studied the stereochemistry Formation of 1-pyrazolinesby the addition of diazoof the preparation of cyclopropanes by this method, methane to double bonds “activated” by electronand concluded that when the intermediate pyrazo- withdrawing groups is often described as a cis addilines are 1-pyrazolines, the cyclopropanes formed ti or^,^-^ but only one study of this point has been retain the geometry of the initial 0 1 e f i n s . ’ ~ ~made.14 ~~ In this study the stereochemistry of the Recent studies have focused on the more complex reaction was examined by the addition of diazoproblem of the stereochemistry of cyclopropane methane to pairs of isomeric a,p-unsaturated formation in cases where the intermediate pyrazo- esters. The first pair, dimethyl citraconate and line is a conjugated 2-pyrazoline.16-15 The explan- dimethyl mesaconate, on treatment with diazoation advanced for the results of these studies is methane gave two liquid 1-pyrazolines, presum&-3,4-dicarbomethoxy-3-methyl-1-pyrazobased on the assumption that 1-pyrazolines indeed ably line ( l a ) and trans-3,4-dicarbomethoxy-3-methyl-l(1) (a) Presented in p a r t a t t h e 138th Aleeting of t h e American pyrazoline (2a), respectively. These pyrazolines Chemical Society, S e w York, S.Y., Sept. 11-16, 1960; ri. Sbstracts had identical physical constant^,'^ but they were of Papers, p . YB P. (bj Portions of t h e present work dealinR with t h e reported to give different products on pyrolysis.16 formation and photolysis of pyrazolines have appeared as a brief communication [K. I,. Rinehart, Jr., and T. V. Van h u k e n . J . Ant 3,4-Dicarbomethoxy-4-methyl-2-pyrazoline (3) was C h ~ m S. O L .82, , A231 (lY6011. (c) T h e earliest brief descriptiun of t h e obtained from both e ~ t e r s . 1 I ~ n the case of the present results including pyrolyses is t h a t uf 13. Wedegaertner, Uniother ester pair, treatment of dimethyl dimethylI ersity uf Illinois Organic Seminar Abstract?, Summer Session [June maleate with diazomethane gave a low-melting 12 3 , 1960. p. 1. 12) (a) I.ubrizo1 Fellow, 1959-1960; Sational Science Foundation pyrazoline, supposedly cis-3,4-dicarbomethoxy-3,4Predoctoral Fellorv, lY60-19B1. (1,) Alfred P. S l o m Fnundation dimethyl-1-pyrazoline (4), while dimethyl dimethylFellow. fumarate and diazomethane yielded a liquid 1( 3 ) T. L. Jacobs, in R . Elderfield, ed.. “Heteracyclic Compounds,” Vol. 5 , John Wiley and Sons. Inc., Sew York, X, Y., 1957, p . 45 ff. pyrazoline reported to be tvans-3,4-dicarbomethoxy(4) B. Eistert, in “Seuere Xethoden der Praparativen Organischen 3,4-dimethyl-l-pyrazoline ( 5 ) . Steric structures Chemie,” Zweite Vlnverandertc Autlage, Verlag Chemie, Berlin, 1045, were not determined experimentally ; cis addition pp. 388-392. was assumed because stereospecific trans addition ( 5 ) A. N. Kost and V. V . Ershov. U s p e k h i Khim., 27, 431 (IS5S). could not be envisioned. No examination of the (6) D. E . .4ppleqnist and I f . E . hlcGreer. J . A m Chem S o r . , 82, 1966 11960). degree of stereospecificity was made. Similarly, (7) K.-D. Grundmann and R. Thomas, B e y . , 93, 883 (1960,. addition of diphenyldiazomethane t o dimethyl RlcGreer, .I Oey. Chem.. 25, 852 11960). citraconatelg and to dimethyl i n e s a ~ o n a t e ~ ~ ~ ~ ~ hlcGreer, 1%‘. TVai and G Carrnichael, C’niz. J . Chenn., 38, 2410 (1960). has also been reported t o produce different pyrazo(10) G. Xomin6 and D. Bertin, B d l . S O L . chin?. Prance, ,520 (1960). lines ( l b and 2b). (11) R . F. Rekker, J. P. Bromhacher and W,T h . N a u t a , Rec. 2rao. In the present work addition of diazomethane chim., 73, 417 (1954). to methyl angelate and to methyl tiglate produced (1) H. L. Slntes and S . I, U’endler, J . .4m. Chem. Soc., 8 1 , 5472 (l9,iY) 3-carbomethoxy-trans-3,4-dimethyl-l-pyrazoline (6) (13) E. K . Trachtenberg and G. Odian, ibid., 80, 4015 (19.58). and 3-carbomethoxy-cis-3,4-dimethyl-l -pyrazolinp (14) K . van Auwers and F. Konig, A n n . , 496, 27 (1932). (7), respectively. These were shown to be dif(15) K. van Buwers and F. Kdnig, ihid., 496, 2.52 (1932). ferent by their n.m.r. spectra (Fig. l ) , and by (16) U’. M. Jones, J . A m . Chem. Soc., 80, 6687 (1958). !17) W.31.Jones, ibid.. 81, 5133 (19.59). (18) \V. hl. Jones, ihin‘., 82, 31:V.i (1960).
(19) W. ll, Jones and \V,-T. T a i , J . O i s . C h n n , 27, 1030 11$162) ( 2 0 ) J. V ~ I IAlghen, R c r . li’nz, r h i m , 62, 3:U il!M‘?).
FORMATIOX . w n DECOMPOSITION OF I -PYRAZOLINES
C k t . 5 . 1962 H.
3737 J
.CH3
=65-
J.72n
C
-
+B=
A
6 5-
1 1
r
b, X=CeH,
552
I 1
-8
-
3-
jED7
c
3
rmrm
2a, X = H
dA
’
6 6 2 630
m1
&a
9‘1 o
~~447
loo
Fig 1 -N m r. spectra of 3-carbomethoxy-cis-3,4-dimethvl-1-pyrazoline (7) (top) and 3-carbomethoxy-trans3,4-dimethyl-l-pyrazoline ( 6 ) (bottom) in carbon tetrachloride a t 60 Mc.
the incompatibility of the n.m.r. spectra with such structures. That neither pyrazoline 6 nor 7 is a 4carbomethoxy - 3,4 - dimethyl - 1- pyrazoline, which would result from the unexpected a-addition2*of diazomethane is also shown by the n.m.r. spectra. a-Addition has been observed in the addition of diphenyldiazomethane to nitroolefins,2 9 , 3 0 and in the addition of diazomethane to vinyl butyl ether.31 5 In the n.m.r. spectrum of either pyrazoline 6 or 7 (Fig. 1) the two four-peak groups, A and B, are due to the C-5 hydrogen atoms, which split one another, and are also split by the C-4 hydrogen atom to give a t y p i ~ a l ~ABX * , ~ spectrum. ~~ The sharp peak C is due to the ester methyl group, while the complex multiplet D results from the C-4 hydrogen atom, which is split by the two C-5 hydrogen atoms and also b y the C-4 methyl group. The sharp singlet E is due to the unsplit C-3 methyl group, and the doublet F is due to the C-4 methyl group, split by the C-4 hydrogen atom. The values observed for the coupling constants between the C-5 their infrared spectra, which had bands a t 1737 hydrogen atom and the C-4 hydrogen atom are reae ~ the ~ ~ assignments made. and 1731 cm.-’, respectively, due to saturated ~ o n a b l for The assignments of geometry to pyrazolines 6 ester carbonyl,21 and a t 154.5 and 1540 cm.-l, respectively, due to K=N.97?-25 The infrared and 7 are based on the n.m.r. spectra, and on the spectra resemble one another in other respects, results of the light-induced decompositions, which but they are clearly due to different compounds.26 are discussed later. The C-4 hydrogen atom of T h a t neither pyrazoline 6 nor 7 is a 2-pyrazoline Soc., 50, 123 (1928)l; (b) C. G . Overberger and J:P, Anselme, ibid., is shown by the lack of X-H stretch in the infrared 8 4 , 869 (1962). ( 2 8 ) T h e term “a-addition” is used t o indicate addition of diazospectra, and by the ultraviolet spectra, which in such a manner t h a t t h e new carbon-carbon bond forms showed Xmax 322 m,u ( E 212) in each case,27and by methane a t t h e a-carbon of t h e unsaturated compound, while 8-addition indicates addition in t h e reverse manner. 6-Addition is usually observed (21) L. J. Bellamy, “ T h e Infra-red Spectra of Complex Molecules.” 2nd ed., John Wiley and Sons, Inc., S e w York, h-.Y . , 1958, p. 179. [see R. J. Landborg, Ph.D. Thesis, S t a t e University of Iowa, 19601. ( 2 2 ) G. P . Mueller a n d B. Riegel, J . A m . Chem. Soc., 76, 3686 (29) W . E. P a r h a m , C. Serres and P . R. O’Connor, J . A m . Chem. (1954). Soc., 80, 588 (1958). (30) W.E. Parham, H. G. Braxton, Jr., and P. R. O’Connor, J . ( 2 3 ) J. A. Moore, J . Org. Chem., 2 0 , 1607 (1955). Org. Chem., 26, 1805 (1961). (24) R. Wiechert and E. Kaspar, Bet’., 93, 1710 (1960). (31) I. A. D’yakonov, Z h f i r . Obshchei Khiiii., 17, 67 (1947); c.f. (25) 5. A. Moore, m‘. F. Holton and E. L. Wittle, J . A m . Chein. Soc., 8 4 , 390 (1962). C.A . , 4 2 , 902h (1948). (32) J. A. Pople, W. G. Schneider a n d H. J. Bernstein, “High( 2 6 ) These spectra m a y be seen in t h e Ph.D. thesis submitted b y Resolution Nuclear Magnetic Resonance,” McGraw-Hill Book Co., T . V. V a n Auken t o t h e University of Illinois, available from University Microfilms. Inc., h-ew York, S.Y . ,1959, p. 132. (33) L. M. Jackman, “Applications of Suclear Magnetic Resonance (27) (a) Ultraviolet spectra of only three other 1-pyrazolines have been reported. These had Xmnl a t 320 mw“ and a t 329 r n p . ~ ~ , ~ i bSpectroscopy in Organic Chemistry,” Pergamon Press, I i e w York, Aznmethnne has Xmsx a1 : N O mi/ [H. C. Ramspergcr, 3 . .41iz. C‘hein. s.Y., 1959; fa) p. 90; (b) p. 85.
3738
THOMAS
v. VAN .!iUKEN
AND
KENNETHL. RINEHART, JR.
Vol. 84
pyrazoline 7 appears a t lower field than does that of pyrazoline 6 because of the unshielding effects of the adjacent cis-carbomethosy group. The methyl angelate used to prepare pyrazoline 6 was found by gas chromatography to contain 3-4% of methyl tiglate. If addition of diazomethane were a nearly stereospecific process, then pyrazoline 6 would contain about 3y0 of pyrazoline 7. The infrared spectrum of pyrazoline 7 shows a band a t 1125 cm.-' having E 10.5. (For comparison, the ester carboxyl band of pyrazoline 7 a t 1737 cm.-' has E 34.3.) This band is not present in the infrared spectrum of pyrazoline 6. Calculations indicate that 5y0of pyrazoline 7 in pyrazoline 6 should be detectable by means of this band, but since it does not appear a t all in the spectrum of pyrazoline 6, no more than 2% of pyrazoline 7 could have 10 11 been formed by addition of diazomethane t o A methyl angelate. Thus the reaction must be a t 4+ 95% 5% least 98y0stereospecific. It is probably completely A so. This is in better agreement with the molecular 5 --f very small amount main product mechanism proposed by Huisgen, Stangl, Sturm and UTagenhofer for this reaction,34than with an Thermal decomposition of cis-pyrazoline 1b ionic mechani~m.*.3~ has been r e p ~ r t e d ' ~to, ~ ~ produce tvans-cycloThermal Decomposition of 1-Pyrazo1ines.-The propane gb, while trans-pyrazoline 2b has been formation of cyclopropanes by the thermal decom- reported?O to form the same compound. The position of 1-pyrazolines has been generally ac- structure of compound 9b was estzbkhed by a cepted as a stereospecific reaction proceeding with negative bromine test, a negative permanganate retention of g e ~ m e t r y , ~ ~ * + and ' ~ - ' ~has been test,20 and failure of the corresponding acid to mentioned as having. "been clearly shown to occur crystallize, l 9 even when seeded with the crystalline stereospecifically."18 Nevertheless, like the forma- acid corresponding to cyclopropane 8b.I9 tion of l-pyrazolines, the stereochemistry of this I n the present study the mixture formed by reaction has been examined in only one study.I5 thermal decomposition of 3-carbomethoxy-transvon Auwers and Konig reported that on thermal 3,4-dimethyl-1-pyrazoline (6) has been shown by decomposition trans-3,4-dicarbomethoxy-3-methyl-gas chromatography to consist of four products1-pyrazoline (2a) gave tmns-l,2-dicarbomethoxy-methyl 2,3-dimethyl-3-butenoate (12), l-carbo1-methylcyclopropane (8a) as the main product, methoxy-trans-l,2-dimethylcyclopropane( 13), 1along with a very small amount of dimethyl p- carbomethoxy - cis - 1,2- dimethylcyclopropane (14) methylita~onate.'~Similarly, the isomeric cis- and methyl 5,3 - dimethyl - 2 - butenoate (15)--in 3,4-dicarbomethoxy-3-niethyl-l-pyrazoline (1a) was the ratio 0.15: 1.22: 1.00: 1.16. Thermal decomreported to produce mainly cis-I ,2-dicarbomethoxy- position of the cis-pyrazoline 7 formed the same 1-methylcyclopropane (sa) and a small amount of compounds in the ratio 0.24:0.70:1.00:3.73. Pydimethyl dimethylmaleate. The results described rolysis of these pyrazolines, then, in contrast to the for the 3,4-dicarbomethoxy-3,4-dimethyl-l-pyrazoresults of von Auwers and Konig, proceeds with lines (4 and 5 ) were comparable.'6 Thermal de- loss of geometry, although there is a slight degree composition of the trans-pyrazoline 5 was reported of stereoselectivity: 1.22: 1.00 in favor of the to give trans - 1 , 2 - dicarbomethoxy - 1 , 2 -dimethyl- trans-cyclopropane 13 from the trans-pyrazoline 6, cycloprcpane (10) as the main product, along with and 1.00:0.70 in favor of the cis-cyclopropane 14 a small amount of cis-l,2-dicarbomethoxy-l,2-from the cis-pyrazoline 7. Esters 12, 13, 14 and dimethylcyclopropane (11). In the case of the 15 were shown to be stable under the reaction concis-pyrazoline 4 the amounts were reversed, 570 pf ditions. the trans-cyclopropane 10 and 95yo of the cisThe structures of the unsaturated esters 12 and cyclopropane 11 being von Auwers 15 were established by their infrared and n.m.r and Konig also reported that 3-carbomethoxy- spectra, and by comparison with authentic samples. cis - 3,4 - dimethyl - 1 - pyrazoline (7) on pyrolysis Ester 12 showed absorption a t 1737 (unconjugated formed a mixture consisting of 77% methyl 2,3- ester), 1645 (double bond) and 898 c m - ' (CH-). dimethyl-2-butenoate (15) and 23% l-carbometh- The n.m.r. spectrum of this compound showed oxy-cis-l,2-dimethylcyclopropane (14) .I5 The geom- peaks a t r3' 5.21, 6.42, 6.94 (quartet, J = 7 c.P.s.), etry of cyclopropane 14 was assigned only by 8 28 and 8.78 (doublet, J = 7 c.P.s.) due, respectively, to the terminal methylene group, the ester analogy with the results just mentioned. methyl group, the a-hydrogen atom (split by the (34) R. Huisgen, 1%. Stanpl, H. J. Sturm and H. Wagenhofer, A w e w . 2-methyl group), the %methyl group and the 2Chem., 7 3 , 170 ( 1 9 6 1 ) . methyl group (split by the a-hydrogen atonl). (35) \V, G. Young, L. J. Andrews, S. I.. Tindenhaurn and S. J. Cristol, J . A m . Chem. Sac., 6 6 , 810 ( l n 4 4 ) . Ester 15 showed infrared absorption a t 1710 (con(36) Preliminary results by t h e present authors tend t o substantiate jugated ester) and 1635 ern.-', and Xmax 221 rnp
+
+
the results reported by von Auwers and Konigls for t h e pyrolysis of the 3,4-~lirnrhomethox~.-3,~-dimethyl-l-pyrazol~nes.
(37) C V. D. Tiers, J. P h y s . Chenz., 62, 1 1 5 1 (19.58).
Oct. 5, 1962
3739
FORMATION AND DECOMPOSITION OF ~-PYRAZOLINES
13
L
j” I 14
,CH3
CH3,
5
I 6.41
I 8.79 9.76 10.0
IC =c‘CO,CH3 CH3
TMS
15 (E 8350), which is characteristic of a trisubstituted a,@-unsaturated e ~ t e r . ~The ~ , n.m.r. ~~ spectrum showed only three peaks a t r 6.37, 8.00 and 8.19, the last two having an area ratio of 1:2. The peak a t r 6.37 is due to the ester methyl group, while the peak a t T 8.00 results from the 3-methyl group cis to the carbomethoxy group. The large peak at r 8.19 is due to the 2-methyl group and the 3methyl group trans to the carbomethoxy group combined.40 Authentic samples of esters 12 and 15,prepared by the Reformatsky reaction of methyl a-bromopropionate with acetone followed by dehydration of the resulting hydroxy ester with phosphorus oxychloride and pyridine, showed identical gas chromatographic retention times, and identical spectral properties with the unsaturated esters obtained from thermal decomposition of pyrazolines 6 and 7. Cyclopropanes 13 and 14 were identified by their infrared, ultraviolet and n.m.r. spectra. I n the infrared these compounds had carbonyl absorption a t 1720 cm.-l, but no double bond in the 1700-1600 cm.-’ region. In the ultraviolet they had only end absorption. No absorption due to vinyl hydrogen atoms appeared in the n.m.r. spectra (Fig. 2), but in the region of r 8.7 to 9.8 appeared cyclopropane hydrogen atoms split into a complex pattern and partly obscured b y absorption due to methyl groups. That these compounds are different is clearly shown by their different infrared2%and n.m.r. spectra, and by their different gas chromatographic retention times. Geometric assignments were made on the basis of competitive saponifications in which the less hindered carbomethoxy group of ester 14 was consumed more rapidly than that of ester 13.44 (38) E. A. Braude and E. A. Evans, J . Chem. Soc., 3331 (1955). (39) A. T. Sielsen, J . Oug. Chem., 22, 1539 (1957). (40) This assignment is preferred rather t h a n t h e alternative assignment of t h e r 8.00 peak t o t h e 2-methyl group, and t h e r 8.19 peak t o both t h e 3-methyl groups because t h e vinyl methyl groups of 3-methyl-2-butenoate appear a t r 7.92 a n d 8.16,“and those of methyl angelate appear a t T 8.02 and S,il,41-43 while those of methyl tiglate appear a t T 8.18 and 8.22.4*-‘a (41) L. M. Jackman and R. H. Wiley, J . Chem. Sac., 2886 (1960). (42) R. R. Frazer. Can. J . Chem., 38, 549 (1960). (43) K. L. Rinehart, Jr., and T. V. Van Auken, unpublished results. (44) T h e geometries of cis-lrans-acid pairs have been established by their relative rates of esterihcation.‘s.4~
6.38
8.76
10.0
Fig. 2.--N.m.r. spectra of l-carbomethoxy-cis-l,2-dimethylcyclopropane ( 14) (top) and l-carbomethoxy-tvans1,2-dimethglcyclopropane (13) (bottom) in carbon tetmchloride at 60 Mc.
In light of our discovery that 1-pyrazolines undergo pyrolysis without stereospecificity, i t is perhaps appropriate to examine evidence relating to pyrolyses of 2-pyrazolines and the rule proposed by Jones16-18 that “the geometrical configuration of the primary cyclopropane resulting from the decomposition of a 2-pyrazoline is determined by the relative thermodynamic stabilities of the intermediate 1-pyrazolines.” In propounding this rule and in using i t to make configurational assignments for cyclopropanes, it was assumed from the work of von Auwers and KOnigl6that 1-pyrazolines decompose stereospecifically t o cyclopropanes. As the present results demonstrate that pyrolysis of 1-pyrazolines may proceed with loss of geometry, the rule cannot be considered to have general validity. The geometry of the predominant cyclopropane formed may be determined in the transition of the 2-pyrazoline t o an intermediate 1pyrazoline, but i t may also be determined in the decomposition of the intermediate 1-pyrazoline. Individual cases thus warrant closer inspection. (45) J. J. Sudborough and L. L. Lloyd, J . Chem. Sac., 73, 81 (18eratilres has not p r r i v r d reproducilile.
(,il>A . XVettstein, H e k . Chirii Acla, 27, 1803 (1944). ( 5 2 ) A. Sandoval, C . Rosenkranz and C. Djerassi, J .
.4717.
C'I!rIl?.
Soc., 73, 2383 (1961). (53) D. E. McGreer, P h . D . Thesis, Univ. of Illinois, 193!1, P 22. (Tr4) W. I. An-ad, S. hl. Xhdel, R . O m r a n a n d 11,Solllly, .I. OK%'. Ch??>z,,26, 4128 (1981).
Oct. 5, 196-3
FORMATION AND DECO?vIPOSITION OF
1-PYRAZOLINES
3741
changed slightly. Rotation about the former C-3; C-4 bond must take place in either intermediate 18 or 19 before cyclopropane is f ~ r m e d . ~ ” The possibility that the pyrazolines themselves isomerize is excluded, since the infrared spectrum of pyrazoline 7, after partial pyrolysis, showed no bands attributable to pyrazoline 6. The zwitterion 19 is a resonance form of the singlet diradical 20, and analogs of both forms lead to the expectation cv clopropanes c H ~ L H, C that this species should cyclize immediately. H CO-CHI X primary carbonium ion would react vigorously 20 with a carbanion, and geminate radial p a i r P are known t o couple very rapidly.57 Thus, it does r i g 3 --Possible ionic mechanism of thermal decomposition. not seem likely that loss of geometry would take If the diradical species 20 were in the triplet place in step c alone,js although rotation in a state, it would not be a resonance form of zwitterion singlet diradical species has been suggested to 19. Intermediates of this type have been sugexplain the thermal isomerization of cyclopropane- gested to account for the lack of stereospecificity d2.59 Loss of geometry could take place prior to observed in the addition of methylene to olefins the formation of species 19, however, by rotation in both the vapor phase,63 and in solution.64 of the diazonium ion 18. Step b involves the -4 diradical species analogous to the diazonium ion formation of a primary carbonium ion from the cor- 18 might also be considered as a possible intermeresponding diazonium ion. This has been esti- diate in the thermal decomposition of I-pyrazolines, matedfioto have an energy of activation of 3-5 but this is unlikely since in azo compounds apkcal./niole. If the negative charge in the diazo- parently both carbon-nitrogen bonds break simulnium species 18 is delocalized into the ester group taneously.65 so that C-3 is essentially planar, then rotation Vi-hen larger groups are present, any of these about the C-3:C-4 bond might compete with loss routes would predict an increase in stereoselectivity of nitrogen. This rotation involves consecutive as a result of more hindered rotation This was eclipsed interactions of methyl-carbomethoxy and observed by von Auwers and Konig Similarly, methylenediazonium-methyl. The barrier to ro- stereoselectivity should be reduced or lost when tation through these conformations should be the pyrazoline is modified in such a may as to greater than the 4.4-6.1 kcal./mole estimated61,62 increase the stability, and hence the life-time, for the eclipsed methyl-methyl interaction in of the intermediates involved. This could explain butane. Thus loss of nitrogen should be slightly the loss of stereoselectivity 27b in favored over rotation, and some degree of stereo- 2-pyrazolines having phenyl groups in the 3- and selectivity would be expected. Step d offers the 5-positions, if geometry is being lost in the depossibility of an N type displacement of the di- composition of the l-pyrazoline rather than conazonium group by backside attack of the C-3 version of the 2-pyrazoline to the 1-pyrazoline carbanion. This should involve a lower energy It is of some interest to examine the possible of activation than step b, but a considerably higher routes of thermal decomposition in view of the entropy factor, since exact orientation about the much greater stereospecificity of photolytic decomposition. Photolysis would be expected to C-4:C-5 bond is required. lead to a higher energy intermediate than pyrolysis, so that an excited singlet might be formed by (,55) Unsaturated ester formation is not discussed since t h e principal the former, and a ground-state singlet might be point under study is t h e retention or loss of geometry in the cyclopropanes. Unsaturated ester formation b y either a n ionic route (proton formed by the latter (but not the reverse) Howo r hydride transfer) or b y a radical mechanism doe4 not contrihute ever, the stereochemistry observed is contrary t o this point. to this supposition. An attractive alternative (56) G. S. Hammond, C.-H. S.W u , 0. D. Trapp, J. IVarkentin and route for the photolysis of 1-pyrazolines involves a R. T. Keys, J . Am. Chem. Soc., 82, 5394 (1980). (57) C. Walling, “Free Radicals in Solution,” John Wiley and molecular mechanism with a transition state such Sons, I n c . , New York, N.Y . ,1957, p. 76ff. as 21 Stereospecific regeneration of methyl (58) If rotation took place partially in species 18. so t h a t 19 were tiglate and methvl angelate could then be exformed in a conformation such as 19a, from which ring closure is not possible without further rotation, then completion of loss of geometry might take place in t h e zwitterion 19.
Y
CHs
19a (59) (a) B. S.Rabinovitch and D. W. Setser, J. A m . Chem. SOC., 83, 750 (1961); (b) E. W. Schlag and B. S. Rabinovitch, ibid., 82, 5996 (1960). (60) A. Streitwieser and W. D. Schaeffer, ibid., 79, 2888 (1957). (61) K . Ito, ibid.,7 6 , 2430 (1953). (02) K . S. I’itzer, C h e v ? , RpamY., 27, 39 (1940).
21 (63) (a) F. A. L. .4net, R . F. TA’ Bader and A.-hI. Vander Auwera. J . A m . Chem. SOC.,82, 3217 (1960); (b) R . XI. Etter, H. S. Skovronek and P. S Skell, ibid.,81, 1008 (19.59); (c) H. RI. Frey, ibid., 82, 5947 (1960); (d) D . B. Richardson, 41. C. Simmons and I. Dvoretzky, ibid., 82, 5001 (1960). (64) K . R . Kopecky, G. S. Hammond and P. A. Leermakers, ibid., 83, 2397 (1961). 16.5) (a) S. G. Cohen and C. H. Wang. ibid , 77, 3628 (19:s); (b) C. G. Overberger a n d A. V. DiGiulio, ibid., 81, 2154 (1959); ( c ) S. Seltzer, ibid., 83, 2625 (1901).
3742
THOMAS v. V A N
AUKEN AND
KENNETH L. RINEHART, JR.
Vol. 84
plained through a similar transition state (22). The possibility that these unsaturated esters were forined by loss of the eleiiients of diazoniethane as nitrogen and methylene in two steps was also considered. A photolysis of pyrazoline 7 in cyclohexene, designed t o trap any methylene formed, gave no bicyclo [2.1.0]heptane, but this is not regarded as definitive. From the present data and from earlier results of others, no definitive choice can be made among these mechanistic possibilities.
1.4482 (lit.71n Z o1.4463), ~ in 500 g. of dry benzene was added during 1.5 hours to 38 g. (0.58 mole) of zinc in 550 ml. of dry benzene heated n t reflux. IIeating and stirring were continued for 3 hours. The mixture was cooled, and then stirred for 1 hour with 750 ml. of 12 N sulfuric acid. The layers were separated and the aqueous layer was extracted twice with benzene. The original organic layer was washed successively with water, saturated sodium bicarbonate solution, and water, and then dried over magnesium sulfate. Solvent was removed under vacuum. Distillation of the residue through a 3-ft. Podbielniak column72 gave 30 g. (3470) of the hydroxy ester, n p 51.4260, ~ which showed infrared bands a t 3520 (OH), and 1735 and 1718 c ~ n . - l (carbonyl of hydroxy ester's), and gave only one peak on gas chromatography (4-ft. didecyl phthalate and 4-ft. Experimental66 silicone grease columns). 3-Carbomethoxy-trans-3,4-dimethyl-l-pyrazoline( 6 ) . T o a solution of 28.6 g. (0.198 mole) of the hydroxy ester A solution of 11 g. (0.26 mole) of diazomethanees and 3.3 g. in 710 g. of pyridine, cooled to so, 155 g. of phosphorus (0.029 mole) of meth\-l angelate [prepared by the method of oxychloride was added. The mixture stood for 10 hours, Dreiding and PrattGg; b.p. 124-127", n a s 1.4294 ~ (lit.e9 and then was heated on the steam-bath for 4 hours. After b.p. 124.2', nZ5D1.4303), which was shown by gas chroma- cooling the solution was poured into ice and water. The tography (4-ft. didecyl phthalate column, 110') to contain resulting mixture was extracted with hexane, and the 37, methyl tiglate] in 400 ml. of ether was allowed to hexane extracts were washed with 2 N hydrochloric acid stand for 4 days. Excess diazomethane was destroyed by and water, and dried over magnesium sulfate. Removal addition of formic acid. Then the solution was washed of solvent under vacuum left a residue of 20.2 g., which was with saturated bicarbonate solution and water, and dried shown by gas chromatography (4-ft. didecyl phthalate over magnesium sulfate. Removal of solvent under vacuum column) to contain 3.2 g. (13% yield) of methyl 2,3-digave 3.6 g . of crude pyrazoline. Fractionation of this methyl-3-butenoate (12) and 11.5 g. (46% yield) of methyl gave 2.0 g. (47%) 2,3-dimethyl-2-butenoate through a Holzman semi-micr~column~~ ( 15). Analytical samples were of 3-carbomethoxy-lrans-3,4-dimethyl-l-pyrazoline ( 6 ) , b.p. obtained by gas chromatography. Methyl 2,3-dimethq-I-354-55' (0.5 mm.), n% 1.4509; ,A, 235 r n M (E 72), 233 butenoate (12) showed infrared absorption a t 1737 (satumM (E 213). The compound showed infrared absorption at rated ester), 1645 (double bond) and 898 cm.-l (CHz=), 1737 (unconj. ester) and 1545 cm.-l (N=N), while no and n.m.r. absorption a t 737 5.21, 6.42, 6.94 (quartet, absorption appeared in the 3600-3100 and 1700-1600 cm.-' J = 6.9 c.P.s.), 8.28 and 8.75 (doublet, J = 0.9 c.11.s.) regions. The n.m.r. spectrum is shown in Fig. 1. (assignments in discussion). Anal. Calcd. for C7H12N202: C, 53.82; H, 7.74; N, Anal. Calcd. for C7H1202: C, 65.58; H, 9.44. Found: 17.93. Found: C, 53.89; H, 7.77; N, 17.92. C, 65.59; H, 9.43. 3-Carbomethoxy-cis-3,4-dimethyl-l-pyrazoline(77.Methyl 2,3-dimethyl-2-butenoate ( 12) had 11% 1.4439,14 A solution of 16.8 g. (0.4 mole) of diazomethanees and 14.8 A,, 221 mp ( e 8350), infrared absorption at 1710 (coi?j. g. (0.148 mole) of tiglic acid in 700 ml. of ether was allowed ester) and 1638 crn.-l (double bond), and n.1n.r. absorption to stand for 5 days. The reaction mixture was worked up at T 6.40,8.02 and 8.21 (assignments in text). in the same manner as for pyrazoline 6 , leaving 22 g. of Anal. Found: C, 65.33; H , 9.49. crude pyrazoline. Distillation through a Holznian semiB. From Pyrazoline Decompositions.-Methyl 2,sm i c r o c o l ~ m n gave ~~ 14.4 g. (62%) of 3-carbomethoxycis-3,4-dimethyl-l-pyrazoline(7), b.p. 72-73' (1.5 mm.), dimethyl-2-butenoate (15), formed in the pyrazoline decompositions described later, was isolated by gas chronian Z s ~1.4561 [lit.14 b.p. 80-82' (2 mm.)]. Redistillation tographic collection (4-ft. didecyl phthalate column). through the same column gave a n analytical sample, b.p. 98-101" (I1 mm.), n% 1.4546, A,, 323 m# ( e 212). The I t showed infrared, ultraviolet and n.m.r. spectra, and gas infrared spectrum showed absorption at 1734 (unconj. chromatographic retention time identical with those of the ester) and 1540 cm.-' (N=N), with no absorption in the authentic sample just described. Methyl 2,3-dimethyl-3-butenoate ( 12), also formed iri 3600-3100 and 1700-1600 cm.? regions. The n.m.r. the pyrazoline decompositions described later, was isolated spectrum is shown in Fig. 1. by gas chromatographic collection (8-ft. silicone grease Anal. Found: C,54.03; H,7.89; Pi, 17.73. column). It was identified by an infrared spectrum, and Methyl 2,3-Dimethyl-3-butenoate(12) and Methyl 2,3- by a gas chromatographic retention time identical with Dimethyl-2-butenoate (15). A . From the Reformatsky the authentic sample decribed previously, and by an Reaction.-A solution of 150 g. (2.58 moles) of acetone those of spectrum of a mixture of methyl 2,3-dimethyl-3and 95 g. (0.58 mole) of methyl 0-bromopropionate, w Z 5 ~ n.m.r. butenoate ( 12) and l-carbomethoxy-trans-2,3-dirneth~lcyclopropane ( 13) obtained by gas chromatographic col( 6 6 ) Gas chromatographic analyses were carried out on a n F and 3!I lection (4-ft. didecyl phthalate column). The ultraviolet Gas Chriimatograph, model 202, and o n a Perkin-Elmer vapor fracspectrum of this mixture showed only end absorption. tometer, model 154b, using helium a s t h e carrier gas, and firebrick a s Identification of l-Carbornethoxy-trans-1,Z-dimethylthe liquid phase support. Ultraviolet spectra were measured in 95% cyclopropane (13) and 1-Carbomethoxy-cis-1 &dimethylethanol on a Cary recording spectrophotometer, model 14h.l. Infrared cyclopropane ( 14). A . Isolation.-1-Carbomethoxy-czsspectra were determined in carbon tetrachloride on a Perkin-Elmer 1,2dimethylcyclopropane (14), obtained from the pyrazospectriiphutometer. model 2 1 B , with sodium chloride optics. N . m r. line decomposition mixtures by gas chromatographic colspectra were measured in carbon tetrachloride with a Varian highlection (8-ft.silicone grease column, 4-ft. didecyl phthalate resolution spectrometer (model V4300B with super stabilizer) a t 60 Mc, column), had n% 1.4289. It showed infrared absorntion using tetramethylsilane as an internal standard. Refractive indices at 1720 cm. (saturated ester) with no bands in the 1700are corrected57 t o 2 5 O . We are indebted t o Mr. J. Xemeth, Mrs. A. 1600 region, and showed only end absorption in tllc Bay, Mrs. E . J. Carey and Miss J. Liu for t h e microanalyses, t o Mr. ultraviolet. The n.m.r. spectrum is shown in Fig. 2. J. Chiu and Miss C. Juan for t h e ultraviolet spectra, and t o Mr. 0. W. h'orton fur t h e n m r. spectra, and t o M r . W. 0. Dalton, hIr. R. H . Johnsun, I I r . D. W.Vittum, Jr., Mr. P. M c l l a h o n and hIrs. 11. 13 l'erkade f u r t h e infrared spectra. (67) N. D . Cheronis and J. B. Entrikin, "Semimicro Qualitative OrSanic Analysis," Interscience Publishers, Inc., New York, h ' . Y., 1D.57, p. 138. ( 6 8 ) 17. Arndt, Org, Sytttheses, Coll. Vol. 11, 165 (1943); see footnote 3 (09) .4. S. Dreiding and R. J. P r a t t , J . A m , Cliein. Sor., 7 6 , 1902 ( 1 9.54). (70) C. XV. G > i i l < l ,Jr , G. T r I s ~ n l aa n ~ d~ C Yiemaiiii, i t o d . C'IICIII., 2 0 , 3Cil (1948).
(71) Tv'. H. Urry and J. R. Eiszner, J . A m . Ckem. Soc.. 1 4 , 8892 (1952). (72) J. Cason and H. Rapoport, "Laboratory Text in Organic Chemistry," Prentice-Hall, Inc., New York, N. Y., 1950, p. 237. (73) (a) 9. J. Leonard, H. S . Gutowsky, W.J. Middletun and E. 11. Petersen, J . Am. Ckem. Soc., 14, 4070 (19.52); (b) S. Searles, 31. Tamres and G. M. Barrow, ibid., 75, 7 1 (1953); (c) H . U . Henbcst, G. 13. 3Ieakins and T . I . Wrigley, J. Ckem. Soc., 2633 ( I n n s ) . (71) A. hf, Gakhokidze, Z k w . Obshchei K h i m . , 11, 1:127 (1047). repurted the improbaldy tiifill nisr, 1 4SSi r-sisof the pyrazoline in contain the two compounds in the ratio 0.77: 1.00: 13: 14. the injection port) indicatiiig that the reaction \\.as coniplete. To this solution 3 mi. of 0.1 ,V aqueous potassium hydroxide In the neat liquid studies the reaction was also followed by \
