SCHMID AND NOWLAN
3086 J . Org. Chem., VoZ. 37, No. 5'0, 1972
The Nonstereospecific Addition of 2,4-Dinitrobenzenesulfenyl Chloride to cis- and trans-Anethole1 GEORGEH.SCHMID" AND VINCENT J. NOWLAN Department o j Chemistry, University of Toronto, Toronto 181, Ontario, Canada Received February 19, 1971 The addition of 2,4dinitrobenzenesulfenyl chloride to cis-anethole in 1,1,2,2-tetrachloroethane(TCE) at 30" gives 30Y0 of the erythro (2) and 70% of the threo (3) Markovnikov adduct, while addition to trans-anethole forms 2 and 3 in 95 and 6% yields, respectively, under the same reaction conditions, The products in TCE at 30' slowly rearrange to an equilibrium mixture containing 51.8% 2 and 48.2y0 3. The nonstereospeeific addition to cisanethole must involve an open carbonium ion prior t o the product-determining step. This result is in contrast to the usual trans addition of aryl and alkylsulfenyl chlorides t o olefins. The addition to trans-anethole is highly stereoselective and it is not clear to what extent an open ion is involved in the reaction.
The reaction of aryl and alkylsulfenyl chlorides to olefins has been found to be a stereospecific trans addition by numerous worker^.^-^ Based upon this observation as well as other evidence, a mechanism involving an episulfonium ion (1) has been postulated for this reactiona6
OCH,
R
/
I
5
4
I
A ,c-c,
OCHS
I
OCH,
I
\
1
We wish t o report the first case of a nonstereospecific addition of an arylsulfenyl chloride t o an olefin and discuss its mechanistic implications.
A r = 2,4-dinitrophenyl
Results The addit'ion of 2,4-dinitrobenzenesulfenylchloride to cis-anethole at 30" in 1,1,2,2-tetrachloroethane (TCE) gives two products, 2 and 3, in 30 and 7001, yields, respectively, while addit,ion t'o truns-anethole forms 2 and 3 in 95 and 5% yields, respectively, under t'he same react,ion conditions. KO difference in product's was observed in the presence of added oxygen or in the presence or absence of light'. It was found that the reaction products in TCE slowly rearrange to an equilibrium mixture which contains 51 .S% 2 and 48.2y03 at 30.92 =k 0.02", in TCE. Compound 2 was obt'ained pure by fractional crystallization of the initial reaction mixture obtained from trans-anet'hole. Despite numerous at'tempts, 3 could not be obtained free of 2. Compounds 2 and 3 are t'he eryt'hro Rlarkovnikov and the threo Markovikov adducts, respectively. Their structures were deduced from the following chemical and spectral information. A mixture containing 6401, 2 and 3601, 3 was dehydrochlorinated by react'ion with diazabicyclononene t o produce a 50 : 50 mixture of cis and t'rans olefins in 85% yield. Four structures, 4-7, are possible for th.ese olefins. The structures assigned to the olefins are based on t'he coupling constant's between the vinyl and methyl protons. For struct'ures 4 and 5 , J should be approximately 2 Hz, while for structures 6 and 7, J should be approximat'ely 7 Ha. Since the observed (1) Reactions of Sulfenyl Chlorides and their Derivatives. VII. Part V I : G . 13. Sohmidand V. M . Csismadia, Can. J . Chem., SO, 2465 (1972). (2) G. H. Schmid and V. M . Csiemadia, Can. J . Chem., 44, 1338 (1066). (3) W. H. Mueller and P.E . Butler, J . Amer. Chem. Soc., 88, 2866 (1966). (4) G. M. Beverly and D. R . Hogg, Chem. Commun., 138 (1966). ( 5 ) W.H. Mueller, Angetu. Chom.,Inl. E d . Engl., 8 , 4 8 2 (1969).
7
6
coupling constants are J = 2.0 and 1.0 Hz, 4 and 5 were assigned the structures of the olefins. These results indicate that the adducts 2 and 3 both have a structure with the chlorine in the 1 position and the ArS group in the 2 position. Additional information regarding the structure of 2 is provided by the following experiment. A pure sample of 2 was solvolyzed in dioxane-water. The resulting alcohol 8 was oxidized to the ketone 9 using OH 2
dioxane water
I AnCHCHCH, 1 SAr
8
0 II
AnCCHCH,
I
*
-
0 I1
AnCCH2CH,
+
ArSCl
SAr
9 A r = p -methoxyphenyl An = 2,4 -dinitrophenyl
the Jones reagent. This ketone proved t o be identical with the a-keto sulfide obtained from the reaction of 2,4-dinitrobenzenesulfenyl chloride and 4-niethoxypropiophenone. Final confirmation that 2 and 3 are configurational isomers is based on a comparison of the nmr spectra of 2 and 3 with the nmr spectra of the addition products of 4-chloro- and 2,4-dinitrobenzenesulfenyl chloride to cis- and truns-l-phenylpropene. The data are
J. Org. Chem., Vol. $7, No. 20,1872 3087
CHLORIDE ADDITION TO ANETHOLE TABLE I NMRDATAOF 2 AND 3 Compd
P~CHCH~CH~Q
I
I
C1 SAr
PhCHaCHbCH3c
I 1
SAr C1
AND THE
ADDUCTS OF 4CHLORO- AND 2,4-DINITROBENZENESULFENYL CHLORIDE TO Cis- AND tranS-l-PHr:NYLPROP~N~ Configuration
6s
loa, 4-Chloro I l a , PCNoro lob, 2,4-Dinitro l l b , 2,4-Dinitro
Ar
Threo Erythro Threo Erythro
4 . 9 7 (d) 4 82 (d) 5 . 1 2 (d) 5 . 0 5 (d)
3 . 6 6 (m) 3.49 (m) 4 . 1 0 (m) 4 . 0 0 (m)
1.23 (d) 1.38 (d) 1.44 (d) 1.63 (d)
12a, CChloro
Threo Erythro Threo Erythro
4 . 3 4 (d) 4 . 2 2 (d) 4 . 7 3 (d) Unknown
4 . 3 4 (m) 4 . 2 2 (m) 4 . 4 6 (m)
1 . 4 4 (d) 1 54 (d) I .56 (d)
4 . 9 2 (d) 5.07 (d)
3 . 9 6 (m) 3 . 9 6 (m)
1.65 (d) 1.43 (d)
13a, C-ChlOrO
12b, 2,4-Dinitro 13b, 2,CDinitro
2 3
given in Table I. The nmr spectra of 2 and 3 are almost idcnt'ical with those of llb and lob,respectively. The isomcrization of 2 and 3 is particularly revealing, since it serves to establish their relative configurations. When 2 isomerizcs to 3 the nmr signal of the methyl group (H,) is shifted to higher field, while the doublet of the methine hydrogen (Ha) is shifted to lower field. If this were a Markovnikov to anti-Narkovniltov isomerization, as found in the case of the adducts of 4chlorobcnzenesulfcnyl chloride to 1-phenylpropene,' the signals for thc methine proton (Ha) would be shifted to higher field, since protons next to chlorine are known to be dcshielded relative tJo protons next to sulfur. Also thc mcthyl protons (H,) would bc shifted to lower ticld. These relationships are evident from a comparison of the chemical shifts of H, and H, in the transformations 10a + 12a, l l a + 13a, and 10b + 12b in Table I. Thcst? observcd changes in chcmical shifts upon isomerization of 2 to 3 as well as the chemical data are compatible wit,h the assignment of t'heir configuration as a pair of crythro-threo Markovniltov isomers. From an examination of the nmr spectra of a series of racemic erythro and t~hrcoisomers, it has bcen found that thc methyl protons of thc crythro isomer always appears a t lowcr ficld than those of t'he threo isomer.6 On this basis, 2 is the crythro 3Iarkovnikov whilc 3 is the threo Markovnikov adduct. The fact that the same two products result from t,he addition of 2,4-dinitrobenzencsulfenyl chloride to cis- and trans-anethole strongly supports this structural assignment'. The kinetics of t8hc addit,ion were carried out a t 30.9'2 0.02" in TCE as solvent. The change in conccntrat'ion of 2,4-dinitrobe1izenesulfenyl chloride with timc was determined by a modification of the usual titration technique used to determine the concentration of sulfcnyl chlorides.? The data gave good straight lines for a second-order reaction, first order in both anetholc and 2,4-dinitrobcnzenesulfcnyl chloridc. Attempts to fit thc data to a first- or third-order kinetic rate law produced curved plots. The second-order rate constants obtained by a least squares fit are listcd in Table 11. The isorncrization of 2 and 3 to an equilibrium mixture was followed by measuring the change in t'he area
*
(6) G . H. Schmid, Can. J . Chem., 46,3415 (1968). (7) N. Kharasch and M. M . Wald, Anal. Chem., '27, 996 (1965).
dc
6b
I
TABLEI1 SPECIFIC RATECONSTANTS FOR T H E ADDITION OF 2,4-I)INITROBENZEN&SVLFENYL CHLORIDE TO CZS- AND trans-l-ANETHoLE trans-Anethole [ArSClIo X 10* mol/l.
[Olefinlo X 108, mol/l.
8.06 7.26 7.63 9.86 7.00 5.72
10.91 11.63 10.68 6.05 13.50 8.45
x
b
M -1
102, seo-1
2.04 2.13 1.89 1.94 1.89 1.93 Av 1 . 9 7 f 0 . 0 9
-
cis-Anethole [ArSClIo X 102, mol/l.
[Olefinlo X lo', mol/].
6.79 5.07 5.54
8.29 9.46 7.19
x loa 3.82 3.87 3,90 Av 3 . 8 6 k 0 . 0 4 k
of their methyl signals in t,he nmr with time. The rate constants obtained by treating the data according to the method of Frost and Pearsons are listed in Table 111. TABLE I11 RAT]
