J. Org. Chem. 1988,53, 2389-2390 2389 CommuntcattonsN .* Organoselenium Chemistry. Preparation and The selenenic acid la was prepared by hydrolysis of the Reactions of 2,4,6-Tri-tert-butylbenzeneselenenic ester lb in aqueous acetonitrile, acetone, or THF (Figure Acid The reaction was monitored by both 'H and I7Se NMR which initially showed formation of methanol and Summary: The preparation and chemistry of 2,4,6-tri- la followed by buildup of the disproportionation products tert-butylbenzeneselenenic acid and several of its esters diselenide 5 and seleninic acid 2a. Under optimum con- and amides are described. ditions as much as 80% of selenenic acid la was present. Both the selenenate ester hydrolysis and selenenic acid Sir: Selenenic acids play a central role in the oxidation disproportionation reactions were strongly solvent-de- and reduction chemistry of Nevertheless, only pendent and were catalyzed by acid and base. In non- areneselenenic acids and esters stabilized by coordination hydroxylic solvents the rate of disproportionation of sel- to ortho nitro or carbonyl substituents have been ob- enenic acid la was much faster than its rate of formation served;1a4$2p3aother selenenic acids disproportionate to by either selenoxide elimination or hydrolysis.6 Com- diselenides and seleninic acids too rapidly to permit pound la was independently prepared by selenoxide spectroscopic observation.'ay2a We not report the first elimination of phenethyl2,4,6-tri-tert-butylphenylselen- observation of a selenenic acid lacking coordinating sub- oxide in aqueous acetone1p8 and was characterized by its stituents that disproportionates sufficiently slowly to NMR spectrum and its chemical derivatization. permit spectroscopic ob~ervation.~ We have used la and lb to test several of the reactions Selenenate ester lb was prepared according to Scheme commonly ascribed to selenenic acids and esters (Table I (Ar = 2,4,6-tri-tert-butylphenyl)by reaction of the sel- I). Benzyl mercaptan, benzylamine, and m-chloroper- enenyl bromide 3 with methanolic sodium methoxide. Dry benzoic acid reacted with la and lb to give the expected selenosulfide 7, selenenamide 6, and seleninic acid 2a and ester 2b. Reaction of selenenic acid la with methanol regenerated lb. The selenenic acid did not react with olefins such as styrene or ethyl vinyl ether; dispropor- 6 R - CICH312CH-CH2 tionation occurred more rapidly than addition. The methyl + selenenate lb, however, reacted over a period of days with 1 2 ethyl vinyl ether to give the acetal selenide 8. solutions of lb were indefinitely stable and could be con- ArSeOCH, t F0A- ArSe OCHZCH' centrated. The ester was characterized by 'H NMR, in "rOCH, which 3JSeH= 9 Hz,~and by I7Se NMR, IR, and mass 4 65% spectroscopy. It was independently synthesized by trans- esterification of the selenenate ester Id which formed by Selenenic acids disproportionate to give diselenides and [2,3] sigmatropic rearrangement of selenoxide 41d and by seleninic acids with an equilibrium strongly favoring the comproportionation'e of the diselenide 5 and the seleninic disproportionation prod~cts.~~~"~~~We also failed to detect acid 2a (see below). The ethyl selenenate IC was also selenenic acid la at equilibrium, but mixtures of diselenide prepared and upon oxidation gave the chiral ethyl sele- 5 and seleninic acid 2a in chloroform reacted with ethyl ninate 2c which showed diastereotopicity in its lH NMR vinyl ether to give the selenide aldehyde 9 and with spectrum. methanol to give methyl selenenate lb in as much as 43% yield, along with methyl seleninate 2b and starting di- selenide 5. We believe that 5 and 2a comproportionated (1)(a) Reich, H. J.; Hoeger, C. A.; Willis, W. W., Jr. Tetrahedron 1985, to form small amounts of la, which was trapped irre- 41,4771. (b) Reich, H. J.; Hoeger, C. A.; Willii, W. W., Jr. J. Am. Chem. versibly by ethyl vinyl ether or methanol. It was confirmed SOC.1982, 104, 2936. (c) Reich, H. J.; Willis, W. W., Jr.; Wollowitz, S. Tetrahedron Lett. 1982,23,3319. (d) Reich, H. J.; Yelm, K. E.; Wol- by independent experiments that selenenic acid la es- lowitz, S. J. Am. Chem. SOC.1983, 105, 2503. Reich, H. J.; Shah, S. K.; terified much faster than seleninic acid 2a. Mixtures of Gold, P. M.; Olson, R. E. J. Am. Chem. SOC.1981,103,3112. (e) Reich, H. J.; Wollowitz, S.; Trend, J. E.; Chow, F.; Wendelborn, D. F. J. Org. 5 and 2b did not react with either methanol or ethyl vinyl Chem. 1978,43,1697.(0 Reich, H. J.; Renga, J. M.; Reich, I. L. J. Am. ether. Chem. SOC.1975, 97,5434. (a) Gancarz, R. A.; Kice, J. L. Tetrahedron Lett. CH,M (2) 1981, 22, 1661. ArSeSeAr t ArSe02H -==- IArSeOHl ArSeOCH, (b) Kang, %I.; Kice, J. L. J. Org. Chem. 1986, 51, 295. (c) Kice, J. L.; - McAfee, F.; Slebocka-Tilk, H. Tetrahedron Lett. 1982, 23, 3323. 5 -20 -10 -lb (3) (a) Rheinboldt, H.; Giesbrecht, E. Chem. Ber. 1955,88,666,1037, 1974. Holzle, G.; Jenny, W. Helu. Chim. Acta 1959, 41, 593. (b) Hori, T.; Sharpless, K. B. J. Org. Chem. 1978,43,1689.Kuwajima, I.; Shimizu, M.; Urabe, H. J. Org. Chem. 1982,47,837. (6)Similar solvent effects have been reported for sulfenic acids. (4).(a) The selenenyl iodide has been prepared: du Mont, W.-W., Shelton, J. R.; Davis, K. E. Int. J. Sulfur Chem. 1973,8,205. Kubhok, S.; Peters, K.; von Schering, H.-G. Angew. Chem. 1987,99,820. (7) For attempts to prepare the analogous sulfenic acid, see: Davis, (b) Ditelluride: Lange, L.; du Mont, W.-W. J. Organomet. Chem. 1985, F. A.; Jenkins, R. H., Jr.; Rizvi, S. Q. A.; Yocklovich, S. G.J. Org. Chem. 286, C1. (c) (2,4,6-Tri-tert-butylphenyl)lithium:Yoshifuji, M.; Shima, 1981,46,3467. I,; Inamoto, N. Tetrahedron Lett. 1979, 3963. (8) Oxidation of neither the selenol (ArSeH) nor the diselenide 5 gave (5)A 3Jh0cH= 7 Hz has been observed for methyl o-carbomethoxy- selenenic acid. benzenese1enenate.lb 0022-3263/88/1953-2389$01.50/0 0 1988 American Chemical Society 2390 J. Org. Chem. 1988,53, 2390-2392 Table I. Svnthesis. Reactions. and "Se Chemical Shifts of la and Related ComDounds no. product (6 We)" starting material reagents yield,b % la ArSeOH (1061c) ArSeOCH, H,O 80 ArSeCHz6HzC6H, mkPBA 60 lb ArSeOCH3 (126gd) ArSeBr CH30Na/CH,0H 78 ArSeOH CH3OH 53 (ArSe)2/ArSeOzH CH30H 43 ArSeCH2CH=C(CH3), m-CPBAICH30H 70 IC ArSeOCHzCH3 (1224d) NaH/CH,CH,OH ArSeBr 70 2a ArSeOzH (1217d) ArSeOH m-CPBA >95 2b ArSeOZCHz(1292d) ArSeOCH3 m-CPBA >95 2c ArSeO2CHZCH3(1282d) ArSeOCHzCH3 m-CPBA >95 6 ArSeNHCHzC6H5(680d) ArSeOCH, C~H~CHZNHZ 95 ArSeOH C~H~CH~NHZ > 95 7 ArSeSCHZC6H6(442d) ArSeOCH3 CGH~CH~SH >95 ArSeOH C&I&HzSH 91 9 ArSeCHzCHO (ArSe,) /ArSe02H CH2=CHOCHzCH3 28' From MezSe. NMR yields. cAcetone-de dCDC13. e Isolated yields. Scheme I esters disproportionate and comproportionate. 1.2 n-&ILl: 5s NaOCH, ArBr - ArSeBr - ArSeGCH, Acknowledgment. We thank the National Institutes 2.b, CHIOH. CH& of Health, NIADDK, for support of this research, and Dr. 3 68% -lb Carl A. Hoeger for exploratory studies on sterically hin- dered selenenic acids.1° Registry No. la, 114031-53-7;lb, 114031-54-8;IC, 114031-55-9; 2a, 114031-56-0;2b, 114031-57-1;2c, 114031-58-2;3,114031-59-3; 5, 20875-32-5;6, 114031-60-6;7, 114031-61-7;8, 114031-62-8;9, 114031-63-9; 2,4,6-(t-B~)~C~H~Br,3975-77-7; 2,4,6-(t- BU)~C~H,S~(CH~)~C~H~,114031-64-0; 2,4,6-(t- 100, I BU)~C~H~S~CH~CH=C(CH3)2, 114031-65- 1. DO h ArSeGCH, ArSeGCH, I ArSeOD - 4 (10) Hoeger, C. A. Ph.D. Thesis, University of Wisconsin-Madison, 1983. Hans J. Reich,* Craig P. Jasperse Department of Chemistry, University of Wisconsin Madison, Wisconsin 53706 Y L I\ \ 1 Received December 18, 1987 Synthesis and Reactivity toward Acyl Chlorides and Enones of the New Highly Functionalized Copper 20 40 60 BO 100 120 Reagents RCu (CN)ZnI Time iminl Summary: The new and highly functionalized copper Figure 1. Hydrolysis of lb in 4% D20/CD3CN at 25 "C. The initial concentration of lb was 0.032 M. The diselenide 5 pre- reagents RCu(CN)ZnI obtained from readily available cipitated and was not measured. primary and secondary alkylzinc iodides by a trans- metalation in THF with the soluble salt, CuCN.2LiX, react Selenenic acid la and its esters are the first to be in good yields with acyl chlorides and enones, respectively, characterized which lack coordination by an ortho sub- to afford ketones and 1,4-addition products. stituent. Despite the size of the 2,4,6-tri-tert-butylbenzene Sir: Copper reagents have proven to be very useful in substituent: selenenic acid la was far less stable than the organic synthesk2 Their synthetic utility would still be o-nitro-, o-benzoyl-, and o-carbomethoxybenzeneselenenic enhanced if highly functionalized copper compounds could acids previously observed.1b~c~2cThe chemical reactivity be prepared. Since lithium and magnesium organo- of selenenic acid la and acid lb was consistent with that metallics are generally used for their synthesis, only a few expected for selenenic acids and esters. In particular, functional groups are tolerated and only a direct synthesis strong evidence for the comproportionation of diselenides using primary alkyl bromides and highly activated copper3 with seleninic acids was obtained. Finally, we have for the allows the synthesis of some functionalized copper reag- first time demonstrated that only the acids but not the ents. The easy generation of functionalized zinc deriva- (9)The size of the tri-tert-butylphenyl group is sufficient to stabilize (1)Undergraduate research.