KETENES. I1
MAY,1964
Ketenes.
1239
11. Cycloaddition of Dialkyl Ketenes to Vinyl Ethers' ROBERTH. HASEK, P. GLEXXGOTT,AND JAMES c. ?\IARTIN' Research Laboratoraes, Tennessee E a s t m a n Company, Davzsaon of E a s t m a n Kodak Company, Kangsport, Tennessee Recezved October 9, 1963
Dimethylketene adds readily to a variety of vinyl ethers to form 3-alkoxy-2,2-dimethylcyclobutanones. Higher dialkyl ketenes, which dimerize much more slowly than dimethylketene, can be forced into cycloaddition t o the less reactive allyl ethers and vinyl esters
The cycloaddition of d i ~ h e n y l k e t e n eand ~ diniethylketene4 t o vinyl ethers was first noted by Staudinger in 1920. A few years ago, Hurd and Kinibrough reexamined the cycloadduct of diphenylketene and ethyl vinyl ether, and corrected Staudinger's original structural assignment by demonstrating that the product was 3-ethoxy-2,2-diphenylcyclobutanone(Ia) .5 They also prepared and characterized the corresponding cycloadducts, I I a and I I b , of ketene and diphenylketene with dihydropyran. Here it was apparent that ketene added to the olefinic bond much less readily than diphenylketene, and in this respect the behavior of the two ketenes followed the relative reactivities in cycloadditions t o cyclopentadiene. 3,6--8 On the other hand, Kinibrough found t h a t diphenylketene failed to yield cycloadducts with higher alkyl vinyl ether^,^ which is rather surprising in view of its well-known ease of addition to a variety of other (and presumably less nucleophilic) olefinic compounds.
I n the light of these observations, the ready addition of dialkyl ketenes t o a variety of vinyl ethers was soniewhat unexpected. The cycloadduct of dimethylketene and ethyl vinyl ether was obtained in 80% yield by adding the ketene to the ether a t room temperature. Formulation of the product as 3-ethoxy-2,2-dimethylcyclobutanone (Ib) vias compatible with infrared and n.ni.r. spectra and with the alkaline degradation t o 3-inethyl-2-butanone. The mechanism of this degradation probably involves an opening of the ring, followed by a saponification and cleavage similar to that of hydroxyniethylene ketone derivatives."
Vinyl ethers with larger alkyl groups, which failed to yield adducts with diphenylketene, reacted readily with dimethylketene to form alkoxy cyclobutanones in good yields. Inert substituents, such as chloro and phenoxy, on the alkyl group had no adverse effect on the reaction. I n a vinyl ether containing an amino group, a vigorous acylation of the amine function ocIIa, R = H b, R=Cs& curred; the derivative then underwent nornial cycloC, R=CH3 addition with i m r e dimethylketene. An attempt to use a vinyl ether containing a tertiary amino group Dimethylketene is rated as less active than diphenylgave only a polymer of dimethylketene, in keeping ketene in cycloaddition reactions.1° For example, with the well-known catalytic action of trialkyl amines dimethylketene does not react with styrene, while on diniethylketene. l 2 diphenylketene f o r m a n a d d ~ c t6a. ~ The reaction Ethyl propenyl ether formed a n adduct with diof dimethylketene with ethyl vinyl ether a t -20' methylketene in good yield, but ethyl isobutenyl ether required three or four days and was accompanied failed to react. The latter addition presumably by some dimerization of the ketene. Seither the failed because steric effects override the nucleophilic yield nor the structure of the product was d e t e r n ~ i n e d . ~ reactivity of the vinyl ether; the inore nucleophilic enamines of analogous structure (isobutenyl amines) (1) Paper I in this series: R . H. Hasek and J. C. Martin, J . Org. Chem., react readily with ketenes.' It is noteworthy t h a t the 38, 1468 (1962). vinyl ethers, unlike enamines, did not form 1 : 2 and (2) To whom inquiries should be sent. (3) H . Staudinger a n d E. Suter, B e r . , S3, 1092 (1920). 1 :3 adducts with dimethylketene; furthermore, (4) €1. Staudinger and P. J. Meyer. Hrlu. Chim. Acta, 7, 19 (1924). the cycloaddition product of ethyl propenyl ether and ( 5 ) C. I). Hurd and R . D. ICinibrough, J . A m . Chem. Soc., 82, 1373 (1060). dimethylketene consisted of two isomers m aniounts ( 6 ) (a) H. Staudinger a n d A . Rheiner, Helu. Chim. Acta, 7, 8 (1924); corresponding to the ratio of cis-trans isaners in the (b) J . R . Lewis. G . R . Rarnage. J. L. Sinionsen. a n d W. G . Wainwright, starting propenyl ether. These results, indicating a J . Chem. S o c . , 1837 (1937). (7) E. H. I'artuer a n d >I 0. . Farooq, ibid., 1925 (1938); L. I. Sinith. 1 : 1 stereospecific addition, are too fragmentary to C . L. Agre. R . bl. Leekley, a n d W. W. Pritchard, J . A m . Chem. Soc., 61, afford any significant conclusions, but they suggest 7 (1939); C. S. Marvel a n d .\I I..Kohan, J . Org. Chrm., 16, 741 (19.51). that the cycloaddition of ketenes to vinyl ethers is a (8) 1%. T. I3rooks and 0.Wilbert. 1. A m . Chem. S o c . , 63, 870 (1941); A . T. Illonrquist and J . Kwiatek, abtd., 73, 2098 (1951); .I. D. Roberts and W. 1;. Gorharn. i h z d . , 74, 2278 (1952); H . L. Dryden, .Jr.. a n d 13. E. I%urgert. % h i d . .77, 5633 (19A.5). ( 9 ) R . 11. ICiti~brough.Ph.D. thesis. Northwestern University, 19.59.
( I O ) J . D. Roberts and C. hI. Sharts, "Organic Reactions," Call. Vol. 12. R . .4datiis, E d . . John Wiley a n d Sons, Inc., New York, N. Y., 1962, p. 27.
(11) E. E. Royals and I
