ABSTRACT2-Diazo-3,3,3-trifluoropropionyl chloride has been synthesized from trifluorodiazoethane and phosgene. Its derivatives are acid stable, can be used to label enzymes, and undergo photolysis with substantially less rearrangement than do derivatives of other known diazoacyl reagents designed for photoaffinity labeling. In particular, the diazotrifluoropropionyl thioester of methyl N-acetylcysteine undergoes photolysis in methanol with about 40% insertion into the -OH bond of the solvent; by contrast, photolysis of other diazoacyl thioesters gives substantially quantitative Wolff rearrangement. The trifluoro compounds hold promise for the photoaffinity labeling of thiols. Photoaffinity labeling was initiated with the photolysis of diazoacetyl chymotrypsin, prepared from the enzyme and pnitrophenyl diazoacetate (1, 2). Subsequently, this and other photolabile reagents have been applied (3-14) to a wide variety of problems in biochemistry and biology. (For reviews, see refs. 15-18.) Diazoacetates and diazomalonates (6, 7), however, suffer from the disadvantages that they are not acid stable, and that photolysis leads in large measure to the products of the photochemical analog of the Wolff rearrangement (2, 19). Furthermore, attempts to use the diazoesters of thiols, either with glyceraldehyde-3-phosphate dehydrogenaset or model compounds (20), have led only to products of the photochemical Wolff rearrangement or to other products that are not informative from the point of view of photoaffinity labeling. In this paper, we report the synthesis and photolysis of diazotrifluoropropionyl derivatives that are not subject to these limitations.2-Diazo-3,3,3-trifluoropropionyl chloride is easily prepared, and is purified by vacuum distillation; p-nitrophenyl diazotrifluoropropionate is a crystalline solid that can be purified by sublimation. Various

The ester acid chloride was treated with dimethylcadmium to form the methyl ketone,13 and this was cyclized with potassium t-butoxide to produce 4,4-dimethylcyclohexan-1,3-dione,13 mp 104.5-106°( lit.13 106°).This dione was produced by an alternate path patterned after a method used to prepare 6-pentacyclohexane-l,3-dione.17 A suspension of sodium ethoxide in xylene was prepared from 17.4 g of ethanol, 6.90 g of sodium, and 200 ml of xylene. To this suspension was added 40 g of ethyl acrylate. While maintaining the temperature at 4°, 13.0 g of 3-methyl-2-butanone was added over a period of 2 hr. After 30 min, the temperature was allowed to rise to 30°, and it was held there until heat evolution subsided. After a further 20 hr at 25°, 100 ml of water was added and the mixture acidified with acetic acid. Ether was added and the ether extract washed with water. The ether extracts from three separate runs were combined, and the solvent was evaporated. Recrystallization of the crude solid from ethyl acetate gave 24.3 g (37%), mp 105-107°. The infrared and nmr spectra were identical with 4,4-dimethylcyclohexane-1,3-dione prepared by the first method, and a mixture melting point showed no depression.

Rhodium(I)-Catalyzed Valence Isomerization of exo-Tricyclo[3.2.1.02 4]oct-6-ene Sir: Valence isomerizations are receiving continuing interest. Recently several examples have been reported

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