3308 J. Org. Chem., Vol. 36, No. 10, 1970
Fluoroketenes
.
ENGLAND AND KRESPAN
IV. Cycloadduct s of Bis(trifluoromethyl)ketene with Acetylenes1 DAVID C. ENGLAND AND CARLG. KRESPAN
Contribution No. 1656 from the Central Research Department, Experimental Station, E. I . du Pont de Nemours and Company, Wilmington, Delaware 19898 Received February 1.2, 19YO Cyclobutenones have been obtained from the reaction of bis(trifluoromethy1)ketene with hexyne-1, butyne-2, phenylacetylene, and diphenylacetylene. Evidence is given for possible mechanisms of these reactions and some unusual chemistry of the products is described. For example, pyf.olysisof the cyclobutenone obtained with phenylacetylene has given five products, 10, 11, 12, 13, or 14, depending on conditions.
Cycloaddition of bis(trifluoromethy1)ketene (1) to phenylacetylene was previously shown to give a cyclobutenone directly.2 This reaction has now been found to have some generality for aryl- and alkyl-substituted acetylenes. Ketene 1 does not react readily with acetylene or ethyl propiolate, probably because of low nucleophilicity of these acetylenes, nor with methylacetylene because of difficulty in obtaining a condensed phase. However, cycloadducts to the carbon-carbon double bond of 1 have been obtained from hexyne-1, butyne-2, phenylacetylene, and diphenylacetylene. Ethoxyacetylene, an exceptionally nucleophilic acetylene, reacts a t the carbonyl group of l to give a different type of products3 As reported earlier,2 phenylacetylene with ketene 1 gave 80% cyclobutenone 2a in a slow reaction at 100". A by-product of this reaction, apparently of structure 3, is formed in good yield by reaction of 2a with phenylacetylene. Characterization of 3 is discussed below.
cyclobutenones with di~henylketene~ and dimethylketene.6 Also, reactions of a number of diethylaminoacetylenes with arylketenes have recently been shown to give cyclobutenones.7 Ring-opening reactions of the new cyclobutenones in every case proceeded by initial scission of the carboncarbon bond between the carbonyl group and the carbon bearing gem-trifluoromethyl groups. Cyclobutenone 2a hydrolyzed readily with warm water to give acid 5 and reacted with fluoride in a liquid phase to form acid fluoride 6. Aqueous alkali followed by acidification resulted in hydrolysis of all fluorine from 2a and formation of the stable acid anhydride 7. Hydrogenation of 2a gave a cyclobutanone 4, identical with that obtained from 1 and styrene. c c F 3 " ~ CEHj - H 2a
(R'= CEH5,R2= (CF,),C=C=O
f R1CECR2 +
I
1. OH-
1
2. H+
%
(CF3),CHC(CGH5)=CHC02H 5
\
(CF,),CHC(C,H,)=CHCOF 6
H 7
H 3
Diphenylacetylene at 200' gave a 95% yield of 2b. Hexyne-1 reacted with 1 at 150" for 8 hr to give a low yield of cyclobutenone 2c. Butyne-2 gave with 1 in 60 hr at 100' a 65% yield of 2d along with a 2: 2 adduct of unknown structure. These cycloadditions with direct formation of cyclobutenones are, with few exceptions, the only such examples known. Previous reactions with other ketenes and various acetylenes have resulted in products of rearrangement^.^ One exception is the additions of ethoxyacetylene which, unlike its reaction with 1, gave (1) Part 111: D. C. England and C . G. Krespan, J . Ow. Chem., 36, 3300 (1970). (2) D. C. England and C. G. Krespan, J . Amer. Chem. Soc., 87, 4019 (1965). (3) F o r details, see part V, J.
[email protected]., 35, 3312 (1970). (4) R. iY.Lacey in "The Chemistry of Alkenes," 6 . Patai, Ed., Interscience, K e w York, N.Y., 1964, p 1161.
Pyrolysis of 2a might be expected to give an a,p-unsaturated ketene 8 in a reversible isomerization.* Ketene 8, a vinylog of ketene 1, could reversibly isomerize to acid fluoride 9 in the same manner as 1 equilibrates with perfluoromethacryloyl f l ~ o r i d e . ~ Products isolated from pyrolyses of 2a in a flow system (5) J. Druey, E. F. Jenny, K . Schenker, and R. B. Woodward, H e l u . Chim. Acta, 46, 600 (1962). (6) R. H. Hasek and J. C. Martin, J . Ow. Chem., 27, 3743 (1962). (7) W. E . Truce, R. H. Baury, and P. 9. Bailey, Jr., Tetrahedron Lett., 5651 (1968). (8) (a) E. F. Jenny and J. D. Roberts, J . Amer. Chem. Soc., '78, 2005 (1956). report evidence for the equilibrium
0
1I
HCCl C
CIH 1I I/ c,H,qo C,H,C-CCI (b) J. E . Baldwin and M . C. MaDaniel, i b i d . , BO, 6118 (1968); (8) y . A . Cheburkov, N . Mukhamadaliev, and I . L. Knunyants, Tetrahedron, 24, 1341 (1968), report reaction of 2s with methanol t o give 1,2 and 1,4 adducts of methanol t o 8 plus a third, uncharacterioed product. (9) D. C. England and C. G. Krespan, J . Amer. Chem. Soc., 88, 5582 (1966).
J . Org. Chem., Vol. $5, No. 10, 1970 3309
FLUOROKETBNES. IV corresponded to the two possible modes of ring closure of the proposed common intermediate, 9. At 350-500°, isomeric ethers 10 and 11 were formed by closure of the six-membered ring, lo and cyclobutenecarbonyl fluoride 12 is also formed by cyclization of 9 as a diene to give a cyclobutene ring. I n these experiments, lower pyrolysis temperatures favored ethers 10 and 11 and higher temperatures favored the cyclobutenecarbonyl fluoride
Pyrolysis of 2b a t 515" gave a product (60%) believed to be the aromatic ketone 18, which could be derived from the expected intermediate 19 by two Friedel-Crafts condensations. r
12. L '
2a
r
18
19
The 2 : l product formed by reaction of 2a with phenylacetylene is, according to spectral data, a conjugated ketone containing two different vinyl protons having a coupling constant of 1.4 Hz. Almost certainly the reaction proceeds by initial scission of the carbon-carbon bond between the carbonyl groups and the carbon bearing gem-trifluoromethyl groups. Products of addition of another mole of phenylacetylene can then be postulated through intermediate 8. 1,4 Addition could give 2Oa or 20b, but 20a can be ruled out
01
20b
20a
14
13
The interrelationship between 10 and 11 on the one hand and 12 on the other through common intermediate 9 was demonstrated by separate pyrolyses of these products. Starting with either a mixture of 10 and 11 or with purified 12, pyrolysis gave the expected mixture of all three compounds. Higher pyrolysis temperatures (600-650") with 2a caused loss of hydrogen fluoride to give 13 and further of carbon monoxide to give rearranged enyne 14. Loss of hydrogen fluoride may have occurred from 12, since the proton was shown to be labile on treatment with base, giving a proton shift to form 15. Simple hydrolysis or methanolysis of 12 gave the unrearranged acid and methyl ester, respectively.
20c
3 20d
C6H5 (GF&
H CGH~
H 12 LE%
21
CF3bCOOH CGH: 15
More direct evidence for the presence of 9 was obtained by isolation of the related butadienyl acid fluoride 16 from the pyrolysis of Zd. Approximately equal amounts of 16 and the corresponding cyclobutene 17 were formed at 500".
I
2d
CH3
because it contains only one kind of vinyl proton. 1,2 addition of phenylacetylene to 8 in the same manner as addition to 1 would give 2Oc which could easily cleave to 20d and cyclize t o 3. Structure 3 is selected over 20b because addition of 1 mol of hydrogen gave an unconjugated ketone 21, whereas addition of 1 mol of hydrogen to 20b would give a conjugated ketone. By forcing the hydrogenation it was possible to add 1 and 2 more mol, giving saturated ketone and alcohol, respectively (detected by mass spectrometry and infrared). It was also possible t o react 1 with p-chlorophenylacetylene to give 2e, and this cyclobutenone reacted with phenylacetylene t o give 22. An isomer of 22 (23)
16 (10) See P. Schiess, H. L. Chia, and C. Suter, Tetrahedron Lett., 5747 (1968),for ri discussion of the tendency for dienones such a8 9 t o exist in the isomerio ZH-pyran form. Although the isomerization 9 11 may be uncatalyzed, the formation of 9 from 8 and the interconversion of cyclio ethers 10 and 11 are probably catalyzed by fluoride ion, iust a s are some analogous reactions starting from ketene 1.
-
p-CIC6Hd (CF3h& \ H 22
C6Hb.
C6H5
CBH4-p-Cl H 23
3310 J . Org. Chem., Vol. 35, No. 10, 1970
was prepared by reacting 2a with p-chlorophenylacetylene.
ENGLAND AND KRESPAN 3,5-Diphenyl-6,6-bis(trifluoromethyl)-2,4-cyclohexadienone
(3). A.-In addition to cyclobutenone 2a in the above reaction there was distilled 2 g of material, bp 168-180" (1 mm), which partly crystallized. Recrystallization from petroleum ether gave 9 g (9.5%) of yellow crystalline 3: mp 120-121"; ir 6.01 (conExperimental Sectionll jugated C=O), 6.12, 6.27, 6.34, 6.38, and 6.72 p (aromatic and conjugated C=C); nmr lH at T 2.70 (multiplet 10, aromatic 1 and Acetylene.-A bomb charged with 36 g of 1 and 26 g CH), 3.18 (doublet, 1, JH/H = 1.4 Ha, =CH), 3.69 (doublet, of acetylene was heated at 150' for 12 hr. The pressure reached was 725 atm. Recovered material boiling above room tempera1, J H / H = 1.4 Hz, =CH); 18F at 61.4 ppm [singlet, (CF3)J; uv ,le;xotane 232 mfi ( 6 14,100), 299 (8300), 329 (8200). ture consisted of 4 g of perfluoromethacryloyl fluoride and 4 g of a Anal. Calcd for CZOHIZFGO: C, 62.88; H , 3.17; F , 29.84. higher boiling mixture. Ir did not indicate the presence of cyclobutenone. Found: C, 62.84; H , 3.02; F , 29.34. 1 and Methylacetylene.-A mixture of 8.5 g of 1 and 3.5 g B.-Compound 3 could be prepared in good yield from phenylof methylacetylene heated in a Carius tube at 175" for 8 hr gave acetylene and cyclobutenone 2a. A mixture of 7.0 g of 2a and 5.0 g of phenylacetylene in a sealed tube was heated 185 hr in a no product. steam bath. The resulting solid was recrystallized from petro1 and Ethyl Propio1ate.-A mixture of 20 g of 1 and 10 g of leum ether to give 7.0 g (73%) of 3, identical with the above by ethyl propiolate heated in a Carius tube in a steam bath 13 days melting point and mixture melting point. The long heating at 150" for 12 hr gave no product. Decomposition occurred at period was subsequently found to be unnecessary. 200". 3,5-Diphenyl-2,2-bis(trifluoromethyl)-3-cyclohexenone(21) 4,4-Bis(trifluoromethyl)-3-butyl-2-cyclobuten-l~one (&).--A from Hydrogenation of 3.--Using a Parr hydrogenator 4.8 g of mixture of 16.5 g (0.20 mol) of hexyne-1 and 37 g (0.21 mol) of 1 the conjugated ketone 3, 50 ml tetrahydrofuran, and 0.1 g was heated in a Carius tube at 150" for 8 hr. There was obPtOz were shaken for 3 hr a t room temperature and 40-psi hydrotained 6.2 g (ll.5yo) of the above cyclobutenone: bp
