J. Org. Chem., Vol. 44, No. 5 , 1979
Cycloadditions of Ketenes and Aldehydes (4)D. W. Jones and G. Kneen, J. Chem. SOC., Chem. Commun., 420 (1973). (5) R. B. Woodward and R Hoffmann, Angew. Chem., lnt. Ed. Engl., 8,839 (1969). (6)D. W. Jones and R. 1.. Wife, J. Chem. Soc., Chem. Commun., 421 (1973). (7)C. K. Bradsher, Adv. Heterocycl. Chem., 16,289 (1974). (8)C. K. Bradsher, F. H. Day, A. T. McPhaii, and P. W. Wong, J. Chem. SOC., Chem. Commun., 156 (1973). (9)C. K. Bradsher and F. H. Day, J. Heterocycl. Chem., 10, 1031 (1973). (10) C.K. Bradsher, F. H. Day, A. T. McPhaii, and P. S. Wong, Tetrahedron Lett.,
4205 (1971). (1 1) Throughout this paper the isomer referred to as syn is syn with reference to the phenylene ring
(12)C K Bradsher, G L B Carlson, N A Porter,andT G Wallis, J Org Chem, 43. 822 --- 119781 (13)C. K. Bradsher and J. A. Stone, J. Org. Chem., 33,519 (1968). (14)C. K. Bradsher and D. J. Harvan, J. Org. Chem., 36,3778 (1971). (15)M. E. Parham, M. G. Frazer, and C. K. Bradsher. J. Org. Chem., 37,358 (1972). (16)Reference 7,p 317. (17)D. L. Fields, T H. Regan. and J. C. Dignan, J. Org. Chem., 33, 390 (1968). (18)I. J. Westerman and C:. K. Bradsher, J. Org. Chem., 43,3002(1978).
--.
\
~
~I
733
(19)D. L. Fields and T. H. Regan, J. Org. Chem., 35, 1874 (1970). (20)Greater accuracy may be achieved by use of more careful integration procedures, cf. L. M. Jackman and S. Sternhell, "Applications of Nuclear Magnetic Resonance in Organic Chemistry", 2nd ed., Pergamon Press, Elmsford. N.Y., 1969,p 52.(21)S.J. Cristol and W. Linn, J. Org. Chem., 34, 1, (1969). (22)D. M. Wieland A. J. McCarty. J. Org. Chem., 37,4285 (1972). (23)K. Hatada, K. Nagata, and H. Yuki, Bull. Chem. SOC. Jpn., 43, 3195 119701 -. (24)W. S.Burnham and C. K. Bradsher, J. Org. Chem., 37,355 (1972). (25)C. K. Bradsher, Acc. Chem. Res., 2, 181 (1969) (26)J. C. Parham, Ph.D. Dissertation, Duke University, 1963. (27)N. L. Allinger and J. T. Sprague, J. Am. Chem. Soc., 95,3902 (1973). (28)P. Crews and J. Beard, J. Org. Chem., 38,522 (1973). (29)R. R. Schmidt and R. Machat. Angew. Chem., lnt. Ed. Engl., 9, 311 \
-I.
(1970). (30)S.Winstein and M. Shatavsky, Chem. Ind. (London), 56 (1956). (31)J. N. Labows and D. Swern, J. Org. Chem., 37,3004 (1972). (32)C. K. Bradsher, J. P. Sherer, and J. C. Parham, J. Chem. Eng. Data, 10,180 (1965). (33)C.K. Bradsher and L. E. Beavers, J. Am. Chem. Soc., 78,2459 (1956). (34)S. Winstein and L. L. Ingraham. J. Am. Chem. Soc., 77, 1741 (1955). (35)The regiochemistry of the addition of 1,1,3-trideutereoindeneto the acridizinium ion has been discussed earler (ref 18).
Trimethylsilylketene. Cycloadditions of Ketenes and Aldehydes William T. Brady* and Kazem Saidi D e p a r t m e n t of Chemistry, N o r t h Texas S t a t e Cnwersit>, Denton, Texas 76203 Receiued July 24,1978 T h e cycloaddition o f trimethylsilylketene w i t h saturated aldehydes in t h e presence o f a catalytic amount o f
BFS.Et20 resulted in the formation o f t h e cis- a n d trans-2-oxetanones. Trimethylsilylketene reacted w i t h a,p-unsaturated aldehydes, cinnamaldehyde, crotonaldehyde, furfural, a n d a-methylcinnamaldehyde, in the presence o f BF,.EtzO, t o yield t r i m e t h y l s i l y l dienoate esters. These esters are derived f r o m t h e 2-oxetanones w h i c h underwent. a silicon m i g r a t i o n f r o m carbon to oxygen accompanied by a ring-opening reaction. Dichloroketene a n d diphenylketene reacted w i t h cinnamaldehyde t o yield t h e corresponding 2-oxetanones, which readily decarboxylated t o the substituted 1,3-butadienes.
Trimethylsilylketene (1) was first reported in 1965 and was prepared by the pyrolysis of (trimethylsily1)ethoxyac-
-( I ) MeLi
EtOCZCH
EtOCSCSiMe,
( 2 ) Me,SiC;I
120
c~
___,
MeSi 'C=C=O
/
H
1
Me ,Si = t r i m e t h y l s i l y l
ety1ene.l The effect of the trimethylsilyl substituent on the properties and chemistry of this ketene is truly remarkable. This ketene is a colorless liquid which boils a t 82 "C, is very stable (and yet an aldoketene, which is most unusual), does not dimerize upon heating, and can be stored for long periods of time.2 Numerous efforts to effect cycloaddition of 1 with a variety of unsaturated compounds have been mostly unsuccessful.* Cycloaddition of 1 with dimethyl- and diethylketene acetals under rather vigorous conditions for a ketene cycloaddition has been r e p ~ r t e dAlso, . ~ the cycloaddition of I with benzaldehyde gave cis- and trans-2-oxetanones, which decarboxylated upon distillation to yield both cis- and trans -trimethyl~ilylstyrenes.~ There are numerous reports in the literature on the cycloaddition of ketenes and carbonyl compounds to yield 20xetanones.j The cycloaddition of ketene with a,p-unsaturated carbonyl compounds has received considerable atten-
tion, primarily in the patent literature, but there is little to be found on the cycloaddition of other ketenes with these unsaturated compounds. This report describes the cycloaddition of trimethylsilylketene with both saturated and a,P-unsaturated aldehydes. Also, we describe the cycloaddition of dichloroketene and diphenylketene with some a&unsaturated aldehydes and the reaction of trimethylsilylketene with ketene bis(trimethylsily1) acetal. Trimethylsilylketene was prepared by the pyrolysis of (trimethylsily1)ethoxyacetyleneand by the dehydrochlorination of (trimethylsily1)acetyl The former method gives a much better yield and was the method most often used. The addition of equimolar quanlities of 1 and simple aldehydes containing a few drops of BF3.Et20 at 0 "C under a nitrogen atmosphere afforded the corresponding 2-oxetanones in 50-60% yields. The 2-oxetanones revealed the carbonyl band in the IR a t 1805-1810 cm-l. The cis and trans i s o m e r s were distinguished on the basis of the cis and trans coupling constants for the methinyl hydrogens in the NMR spectrum. The NMR spectrum of 4-ethyl-3-(trimethylsilyl)-2-oxetanones (2a and 2b) revealed a doublet a t 6 2.8 and a multiplet a t 6 4.0 ( J = 4 Hz) and a doublet a t 6 3.2 and a multiplet a t 6 4.3 ( J = 6 Hz). The larger coupling constant was assigned to the cis isomer. The ratio of cis (2a)ltrans (2b) was 55:45 based on the NMR and VPC data. The 2-oxetanones did not undergo thermal decarboxylation
0022-3263/79/1944-0733$01,00/00 1979 American Chemical Society
Brctdy and Saidi
734 J . Org. Chem., L'ol. 44, No. 5 , 1979 KCHO
+1
b
a
2, R = Et 3, R = n-Pr 4 , R = i-Pr
5,R=
1
a
when heated a t 150 "(2 for 1 h. This is in contrast to most 2 oxetanones which readily decarboxylate upon heating.5 I t is noteworthy that these cycloadditions do not occur in the absence of the BFY.Et20. This complex probably undergoes exchange with the aldehyde, resulting in activation of the carbonyl group to cycloaddition. The reaction of equimolar quantities of 1 and a,@-unsaturated aldehydes containing a few drops of BFY-EtJJ resulted in the formation of the corresponding %oxetanone as evidenced by an IR band at 1805-1810 cm-l of the reaction mixture. However, during the distillation process the silyl iubstituent migrated from carbon to oxygen accompanied by a ring-opening reaction to yield the trimethylsilyl dienoate esters. The esters were isolated in 50-60"h yields and revealed the carbonyl band in the IR at 1685 cm-'. The cycloaddition of 1 with (E)-cinnamaldehyde and (E)-crotonaldehydeyields two silyl esters, 6 c and 6d and 7c 1
+ RCHO
R' b
I
1
>===
