J. Org. Chem., Vol. 58, No. 26, 1975
NOTES
4447
TABLE I11 T], M ; [AgNOa], 0.0100 M ; Titers, ml of 0.00625 14 KC1 A. Temp, 45.0"; 5-ml aliquots; [ C ~ H ~ B 0.0400 0 10.15 15.20 20.34 24.95 Time, min 7.88 7.40 7.19 7.02 6.85 Titer 102 k2 5, M-16 sec-1 2.64 2.60 2.47 2.53 49.90 30.51 40.02 Time, min 6.22 5.92 6.57 Titer 2.69 2.66 2.67 102 k2 5, M-1 sec-1 B. Temp, 45.0'; 5-ml aliquots; [CaHsBr], 0.0800 M ; [AgN03], 0.160 M; Titers, ml of 0.100 M KC1 1.30 2.03 2.66 0 Time, min 7.70 7.30 7.12 7.00 Titer 2.29 2.22 2.11 102 k2.5,M-1 sec-1 3.96 4.54 5.18 Time, min 6.71 6.57 6.50 Titer 2.18 2.26 2.15 102 kz 5, M - 1 sec-1
3.28 6.83 2.23
~ ] , M ; [AgClOd],0.087 M ; Titers, ml of 0.0500 M KC1 C. Temp, 45.0'; 5-ml aliquots; [ C ~ H S B 0.200 Time, min 0 1343 2835 4215 5630 Titer 8.70 8.05 7.48 7.04 6.58 lo5 k2 5, LW-1.5sec-l 1.70 1.62 1.57 1.60 Time, rnin 9970 11458 12903 14393 Titer 5.38 5.17 4.84 4.60 105 k2 5, i M - 1 5 sec-1 1.63 1.64 1.69 1.69
D. Temp, 45.0'; 5-ml aliquots; [C3H&l], 0.0800 fM; [AgN08], 0.0400 M ; Titers, ml of 0.0250 M KC1 Time, min 0 1452 2897 4282 8649 Titer 8.04 7.00 6.23 5.50 4.32 104 k z 8, iM-16 sec-1 0.97 1.03 1.12 1.02 Time, min 10077 11511 12953 14363 Titer 3.98 3.70 3.48 3.28 1.03 1.03 1.02 1.01 104 kz 5, i M - 1 6 sec-1
bromide 80 times faster than silver perchlorate. The corresponding ratio of 1600 for allyl bromide is some 20 times larger and this suggests that in reaction with silvcr nitrate nucleophilic assistancc is more pronounced for allyl bromide than for thc secondary 2-octyl bromide or the tertiary a-brominatcd ketone, a-bromo-p-phenylisobutyrophcnonc, where, at 74.0" and for reaction with 0.16 M salt, a ratio of 130 was observed.10 The leaving-group effect (Table 11) has an average value of 285, which can be compared to a corresponding bromide/chloride ratio of 467 for reaction of 2-octyl While the difference between these ratios is quite small, its direction is consistent with the proposal of more pronounced nucleophilic assistance (less S N 1 character) for reaction of the allyl bromide. At 45", silver nitrate reacts with allyl bromide about eight times faster than with 2-octyl bromide. Streitwieser18reports that, on the average, allyl derivatives react under S N conditions ~ some 1600 times faster than isopropyl derivatives; the rates of isopropyl derivatives can be considered to represent an upper limit for the possible S N rates ~ of 2-octyl derivatives. I n the presence of accompanying electrophilic assistance, the spread between the rates of nucleophilic attack upon allyl bromide and secondary bromides is considerably reduced. Experimental Section Materials.-Allyl chloride and allyl bromide were purified by fractional distillation. Silver nitrate was used as received. Acetonitrile and silver perchlorate were purified as described previously. Kinetic Procedures.-Potentiometric titration to determine the concentration of silver ion remaining in solution and titration of developed acid, in the presence of silver ion, were carried out (18) A. Streitmieser, Jr., Chem. Rev., 56, 571 (1956).
as described previously.2 Reaction solutions were prepared by appropriate dilution of concentrated stock solutions within 50-ml volumetric flasks and, after shaking and temperature equilibration, 5-ml aliquots of solution were removed at appropriate time intervals. Heterogeneous catalysis by precipitated silver bromide was shown to be unimportant by allowing a solution initially 0.08 M in both allyl bromide and silver nitrate to react to 50% completion and then showing the subsequent kinetics to be identical with those of a solution initially 0.04 M in each reactant. Integrated 2.5-order rate coefficients were calculated using the appropriate form for the integrated rate e q u a t i ~ n . ~ , ~ ~ Four illustrative runs are reported in Table 111. Registry No.-Allyl bromide, 106-95-6; allyl chloride, 107-05-1; silver nitrate, 7761-88-8; silver perchlorate, 7783-93-9; acetonitrile, 75-05-8. (19) We wish t o thank Mr. K. C. Kolmyck for writing a computer program for this operat,ion and Mr. A. Wang for applying the program to the experimental results.
Onium Ions. V1II.l Selenonium and Telluronium Ions and Their Comparison with Oxonium and Sulfonium Ions GEORGEA. OLAH,*JAMES J. SVOBODA, AND ALICET. Ku
Department of Chemistry, Case Western Reserve University, Cleveland, Ohio 44106 Received August 7, 1973
A series of trialkyl(ary1)selenonium and telluronium ions are known.2 However, neither were acidic selenonium (telluronium) ions previously obtained, nor (1) P a r t VII: G. A. Olah, J. R. DeMember, Y. K. Mo, J. J. Svoboda, P . Schilling, and J. A. Olah, J . Arner. Chern. Soc., in press. (2) For a summary and references see H. Reinboldt in "Houben-Weyl Methoden der Organischen Chemie," Vol. 9, Georg Thieme Verlag, Stuttgart, 1955, pp 1034, 1975.
4448 J . Org. Chem., Vol. 38, No. 66, 1973
NOTES
TABLEI PMRPARAMETERS OF SELENONIUM IONSAND PARENT SELENIDES* Registry no.
a
Solvent
7783-07-5 42423-18-7 593-79-3 42423-19-8
HzSe HsSe (CH3)2Se ( CH3)nSeH+
cs2 H F (excess)-BF3 so2
7101-31-7 42493-34-5 627-53-2
(CHa)i3ez (CH3)3Se+ a (CH3CHdzSe
so2 so2 so2
+
FSOaH-S bFs-SO2
SeH
Hi
-0.25 5 . 8 0 (s) 4 . 5 0 (sp)
1.66 2 . 9 6 (d, J = 7.OHz) 2.26 2.70 2 . 4 1 (9)
42423-22-3 (CHSCHZ)ZS~H + FSOaHS bF5-SOz 4 . 4 0 (P) 3 . 7 7 (P) 42493-35-6 ( CHaCH2)3Se+ a so2 3 20 (9) As fluorosulfate salts. s = singlet, d = doublet, t = triplet, q = quartet, p = pentuplet, sp = septuplet.
were any of these onium ions studied by nmr spectroscopy To extend our study of onium ions, we prepared and studied the selenonium ion (H3Se+),as well as a series of acidic secondary alliylselcnonium and telluronium ions R&e(Te)H+ in superacid solution. We also prepared and isolated a series of trialkylselenonium and -telluronium ions as well as trialkylsulfonium ions as their fluorosulfate salts. A comparative study of all onium ions by pmr spectroscopy was carried out.
Results and Discussion Hydrogen selenide is very easily oxidized to elemental selenium. As a result, fluoroantimonic acid (HFSbF,) and "Magic Acid" (FSO3H-SbFb), generally used in preparation of acidic onium ions, cannot be used, since they both oxidize hydrogen selenide. We have found, however, that hydrogen selenide can be protonated without oxidation by HF-BF3, in excess H F solution. HnSe .f HE! BF, e H3Se+BF4-
+
The selenonium ion formed in this way a t -70" showed a singlet pmr absorption a t 6 5.8, deshielded by 6.1 ppm from the absorption of parent HzSe. Hydrogen selenide used in the preparation of the selenonium ion was obtained by the hydrolysis of aluminum selenide, A12Se3. Alkyl selenides are much more stable to oxidation than hydrogen selenide, and can be protonated in FSO3H-SbFb-SO2 solution. The dimethylselenonium FSOaH-SbFs
RzSe
--3 R2SeH+ SO,, -60'
ion (protonated dimethyl selenide) shows in its pmr spectrum the methyl doublet a t 6 2.90 ( J = 7.0 Hz) and the SeH septet at 6 4.50 ( J = 7.0 Hz). A double irradiation experiment showed that the doublet and septet are coupled. The pmr spectrum also shows an unidentified small doublet at 6 3.50 and a singlet a t 6 3.80 for the (CH3)zSe-SbFs complex (see subsequent discussion). The diethylselenonium ion shows the methyl triplet at 6 2.00 ( J = 7.0 Hz), the methylene quintet at 6 3.77, and the SeH quintet at 6 4.40. Pmr data of the parent selenium compounds and the corresponding selenonium ions are summarized in Table I. The pmr spectrum of dimethyl selenide in SbFsSOzClF solution at -60" shows a singlet at 6 3.85 of the donor-ac c ept or complex, (CH3) e-S bF5.
1.30 (t, J = 7Hz) 2 . 0 0 (t) 1 . 4 0 (t)
The acidic, secondary alkyl selenonium ions are remarkably stable. The pmr spectra showed no significant change from -60 to 65". Trialkylselenonium fluorosulfates are conveniently prepared by the reaction of diallyl selenide and alkyl fluorosulfate, using 1,1,2-trichlorotrifluoroethane as the reaction solvent. Trimethyl selenonium fluorosulRzSe
+ ROSOZF+R3Se+FS03- (R = CH3, C2H5)
fate thus preparcd is a stable, white solid, mp 83-85", which, when dissolved in liquid sulfur dioxide, exhibits a singlet proton nmr absorption at 6 2.7. Triethylselenonium fluorosulfate was also prepared in the same way. It is also a stable, white solid, mp 25-28". When dissolved in liquid sulfur dioxide, triethylselenonium fluorosulfate shows the methylene protons at 6 3.2 (quartet) and the methyl protons at 6 1.4 (triplet). The parent telluronium ion, H3Te+, could not be observed in superacid solution of hydrogen telluride, under conditions where the selenonium ion is observed. Alkyl tellurides in FSOsH-SbFb solution using SO2 as a diluent at -60" show deshielded alkyl proton chemical shifts, as compared with the corresponding dialkyl tellurides themselves in SO,. This indicates that in this medium the tellurides are protonated, but neither the proton on tellurium nor its coupling was seen. Using HF-BF3 in excess HF solution both the >TeH+ proton and its coupling in secondary alkyl telluronium ions can be observed. R2Te
+ H F + BFa +RzTeH+, BF4-
Alkyltelluronium ions show well-resolved pmr spectra (Table 11). The dimethyltelluronium ion (protonated dimethyl telluride) shows the methyl doublet at 6 2.7 ppm ( J = 7 Hz) and the TeH septet at 6 1.6 ppm. Similarly, the dicthyltelluronium ion (protonated diethyl telluride) shows tho methyl triplet at 6 1.9 ppm, the methylenc quintet at 6 3.4 ppm, and the TeH multiplet, partially overlapping the methyl triplet, at 6 1.6 ppm. Trialkyltelluronium fluorosulfates were prepared similarly to the trialkylselenonium salts from dialkyl telluride and alkyl fluorosulf ate. Trimet hylt elluro(CH3)2Te+ CH30S02F+(CH3)3Te+FS03-
nium fluorosulfate prepared in this way is a stable, light yellow salt, mp 130", which, when dissolved in liquid sulfur dioxide, exhibits a singlet 'Hnmr signal at 6 2.3 ppm. The triethyltelluronium salt could not be isolated, although prepared in solution it is also quite
J. Org. Chem., Vol. 58, N o . 66, 1975 4449
NOTES
TABLE I1 PMR P.4RAMETERS O F ALKYLTELLURONIUM IONS A N D THEIR PARENT TELLURIDESO HI Hz HI H 4 1.60 (s) FS03HSbFsSOz 3 . 5 5 (s) HF-BFj 1 . 6 (SP, 2 . 7 0 (d, J = 7 Hz) J = 7 Hz) so2 2 . 3 0 (s) 42493-33-4 (CH3)3Te+OSOZF2 . 4 0 (4, 1.30 (t, 627-54-3 (CH3CHdzTe so2 J = 7 . 5 H z ) J = 7 . 5 Hz) 4 . 3 5 (9, 2 . 3 3 (t, 42422-97-9 (CI13CE12)zTeH FS03HSbFrSOz J = 7.5H~) J = 7.5H~) (CH3CH2)2TeH+ IIF-BF3 1 . 6 (m) 3 . 4 (m) 1 . 9 (t) 2 . 4 8 (t, 1.46 (m) 1.46 ( m ) 0.80 (t, 38788-38-4 (CIIJCHZCHZCHZ)ZT~ SO2 J = 7 . 3 Ha) J = 7.3 HZ) 4.33 (t, 2 . 4 0 (m) 1.96 ( m ) 1 . 4 0 (t, FS03H-SbFsS02 42422-99-1 ( CI-I~CHzCII~CH~)~TeH J = 7.5Hz) J = 7.5H~) Coupling constants in hertz are given in parentheses following the multia Chemical shifts are in parts per million from external TIIS. plicities: s = singlet, t = triplet, q = quartet, sp = septuplet, m = multiplet. Solvent
Registry no.
TeH
so2
593-80-6 (CH3hTe 42422-95-7 (CH3)2TeH (CH3)zTeH
+
+
+
TAI~LE I11 COMI'.\ltISON OF PMIt
PAR.\METERS OF
ItEL.\TED OXONIUhl,' SULFONIUM,'
+XlI
Registry no.
17009-82-4 18683-32-4
(CHa)zSH
+
(CH3)2SeII
+
(CH3)zTeII 2
+
b
1
17009-83-5
(CHICH~ )zOH
38682-84-3
(CH3CHz)zSII
2
+
+
2 1 + (C I ~ ~ C H Z ) ~ T ~ H *
42423-05-2
3 . 0 8 (d)
8.0
2 . 9 6 (d)
7.0
2 . 7 0 (d)
7 3.6
6 . 2 3 (P, J = 8.OHz)
3.57 (p)
1.67 ( t )
8.0
4,4O (P, J = 7.OHz)
3.77 (p)
2 . 0 0 (t)
7.0
1 . 6 (m)
3 . 4 (m) 4.12 (s) 3.90 (s) 2 . 7 (s) 2 . 3 (s)
1 . 9 (t)
5 . 1 (9)
2.0(t)
3 . 4 (9)
1.8 (t)
1
(CHsCHz)30
+
c
1
(CH,CHZ)~S+ 2
3.4
1.53 ( t )
+
2
4.49 (d)
4 . 7 3 (0)
(CH3)30+ (CHa)ZS d (CH3&3e d (CH3),Te+d 2
JH-k~
8.61 (p, J = 3.6Hs)
+
17950-40-2
Hz
1
2 1 + (CHICIIZ)~S~H
121 16-05-1 42423-04- 1
€I I
10.2 6.60 5.80 9.05 (sp, J = 3.4Hz) 6 . 5 2 (sp, J = 8 . 0 HE) 4 . 5 0 (sp, J = 7.011~) 1 . 6 (SP)
13988-08-6 18155-21-0
SEILNONIUM, A N D TELIXRONIUM IONSo
1
(CH3CH~)3Sed 1 . 4 (t) 3 . 2 (9) In FSO~II-S~E',-SOZ solution at -60', from capillary TNS. Figures in parentheses show multiplicity of peaks: s = singlet, d = doublct, t = triplet, q = quartet, p = pentuplet, sp = septuplet, o = octet, ni = multiplet. * I n HF (excess)-BF~at -60". 111 SO2 :it - 60' ah thc hexafluolophosphate salt. d In 902 a t -60' as the fluorosulfate salt. 0 1)ata summarized in G. A. Olah, A. M. White, :md 1). 11. O'Urieli, Chem. lieu., 70,561 (l970), and references cited thereill. +
(I
stabl(h. No rl(1nvagc of the ions in solution is observed up to 6,j". The. proton on sclcnium in sclenonium ions and on tellurium in tclluronium iom is considerably morc shicldrd than tlw proton on oxygen in the related oxonium ions (6 7.SS-9.21)and the proton on sulfur in thv cwrrcsponding sulfonium ions (6 5.SO-6.52). E'or ('omparison, thv chcmical shifts of thc corresponding oxonium, sulfonium, s(:lcnonium, and tolluronium ions summarized in Tahlc 111. Thcrc is a consistcmt trcwd of incrcasing shielding going from related oxonium to sulfonium to sc~lcnoniumto tdluronium ions (which is particularly significant when considering thc directly
obscrvcd protons on hctcroat oms). Charge delocalization and shielding by incrcasingly heavier atoms is thus indicatrd. Experimental Section Protonation of Dialkyl Selenides and Tellurides in FSOaHSbF6-S02.--Ca. 200 rng of corresponding dialkyl selenide (telluride) was dissolved in about 2 ml of liquid sulfur dioxide and added, with good stirring, to a solution of 2 ml of 1: 1 :4 FS03HSbFs-SOJ (at about -70'). Part of the resultant solution was trnrisferrcd by precooled pipette to the nmr tube. A TMS capillary was inserted and pmr spectra were obtained on a Varian Associates Model 56/60A spectrometer. Protonation of HzSe in HF-BF3.-Approximately 100 mg of
4450 J . Org. Chem., Vol. 58,No. 26, 1973 HZSe (prepared in a side-arm test tube by hydrolysis of AlsSea and condensed in dry Nz atmosphere directly into the nmr tube) contained in a quartz nmr tube was cooled to -78" in a Dry Iceacetone bath. To the nmr tube was added 1 ml of anhydrous hydrogen fluoride and the mixture was agitated to form a clear solution. The solution was then saturated with boron trifluoride. A TMS capillary was inserted and the pmr spectrum was obtained at -80". Protonation of Alkyl Tellurides in HF-BFa.--Approximately 1 rnl of anhydrous hydrogen fluoride was placed into a quartz nmr tube and cooled to -78" in a Dry Ice-acetone bath. To the nmr tube was added 100 mg of alkyl telluride and the mixture was agitated to form a clear solution. The solution was then saturated with boron trifluoride. A TATS capillary was inserted and the pmr spectrum was obtained at -80". Trimethylselenonium F1uorosulfate.-To a solution of 11.4 g (0.1 mol) of methyl fluorosulfate in 50 ml of anhydrous 1,1,2trichlorotrifluoroethane was added a solution of 9.4 g (0.1 mol) of dimethyl selenide in 50 ml of anhydrous 1,1,2-trichlorotrifluoroethane at room temperature. The mixture was agitated for 10 min and the white precipitate was filtered off. The product was twice washed with 1,1,2-trichlorotrifluoroethaneand dried in a stream of dry Nz, mp 83-85'. Triethylselenonium Fluorosulfate .-The procedure was similar to that used for the preparation of trimethylselenonium fluorosulfate except that 12.8 g (0.1 mol) of ethyl fluorosulfate and 10.8 g (0.1 mol) of diethyl selenide were used. In order to isolate the product it was necessary to extend the reaction time at 0" to 1hr, after which the white precipitated triethyl selenonium ion was isolated as before, mp 25-28", Trimethyltelluronium Fluorosu1fate.-The procedure was similar to that used for the preparation of trimethylselenonium fluorosulfate except that 14.3 g (0.1 mol) of dimethyl telluride was used, mp 128-130". All melting points were determined in sealed capillary tubes. They are dependent on rate of heating (2"/min in the melting range, after having determined it by 10" min ) . Trimethylsulfoniurn Fluorosulfate and Triethylsulfonium Fluorosu1fate.-The preparations used were similar to those of the corresponding selenonium ions, using dimethyl and diethyl sulfide, respectively. (CH3)3S'SOaF- had mp 174-176" and ( C2Hj)3S+S03Fhad mp 25'. All isolated onium fluorosulfate salts gave correct elemental analyses.
NOTES
from problems of polyalkylation resulting from proton transfer. A recent paper by Grieco and coworkers prompts us to report our studies in this area.2d The organocopper enolates (1) generated by the addition of lithium dialkylcuprates to enones offer the possibility of eliminating the problems of polyalkylation since these are presumably highly covalent and, therefore, less likely to undergo proton transfer. One also can take advantage of the higher stereoselectivity and generally higher yields of 1,4-addition products produced with the organocopper reagents. We would like to report that these intermediate enolates may be alkylated regiospecifically in unhindered cases without significant amounts of polyalkylation occurring. There has been no direct evidence reported as t o the structure of the intermediate ( l ) , but in our experience, as
-
8 6, &xR' 2
LiCuRl
___t
R
1
well as others,2e the unreactivity of 1 under the normal alkylation conditions (methyl iodide, ether, 25') indicates that the structure is best interpreted as an organocopper enolate. A reprcsentative group of cyclohexenones (Table I) xhich was studied showed that TABLE I Reactions
%
bCH, 0
1
LiCu(CH,),-Et,O,
0
R - CH, R = W
76
R R
95 89
90
'""ecH
2. HMPA-THF-RX
Acknowledgment, -Support of our work by the National Institutes of Health is gratefully acknowledged. Registry No.-Methyl fluorosulfate, 421-20-5; ethyl fluorosulfate, 371-69-7; dimethyl sulfide, 75-18-3; diethyl sulfide, 352-93-2.
Lit
O/CUR
n
0
ACH3 /
=
CH, =
N
92
U C H ,
Regiospecific Alkylation of Organocopper Enolates ROBERT K. BOECKMAN, JR. Department of Chemistry, Wayne State University, Detroit, Michigan 4820d Received June 16, 1973
Regiospecific alkylation of lithium and magnesium enolates, generated from enol acetates' or the 1,4 addition of Grignard reagents,2 has been knovn for some time. The latter process allows the introduction of two diff went alkyl groups in one synthetic operation. However, to varying degrees, these methods suffer (1) H. 0. House and B. bI. Trost, J . Org. Chem., SO, 2502 (1968).
(2) (a) G. Stork, G. L. Nelson, F. Rouesac, and 0. Gringore, J . Amer. Chem. Soc., 93,3091 (1971); (b) G. Stork, Pure A p p l . Chem., 17, 383 (1968); ( e ) P. Hudrlik, Ph.D. Dissertation, Columbia University, 1969; (d) P. A. Grieco and R . Finkelhor, J . Org. Chem., 38, 2100 (1973); (e) G . H. Posner and J. J. Sterling, J . Amer. Chem. Soc., 96,3076 (1973).
Analysis by vpc compared with inde5 Distilled yields. pendently prepared samples.
alkylation can be accomplished regiospecifically and in high yield under mild conditions. Significantly, no evidence of polyalkylation was found even in the presence of excess allyl halides. One limitation of this method (and presumably that of the magnesium enolate also) was encountered. The preservation of enolate regiospecificity during alkylation requires that the rate of alkylation be significantly greater than proton transfer. I n the case of p,p-disubstituted enones this criterion is not met. Treatment of P,P-disubstituted enoncs under the usual conditions for 1,4 addition followed by alkylation rcsulted in varying amounts of equilibration prior to alkylation. As can be seen (Table 11),it appears that reduction
