Inoue, Yoshihiko

Nozawa, Shigeo

Tanimoto, Shigeo

Kyoto University Research Information Repository

Title Base-Induced Cleavage of Sulfur-Sulfur Bond in SeveralDisulfides Having α-HydrogensAuthor(s)Tanimoto, Shigeo; Nozawa, Shigeo; Inoue, YoshihikoCitationBulletin of the Institute for Chemical Research, KyotoUniversity (1990), 68(3): 193-198Issue Date1990-10-31URL http://hdl.handle.net/2433/77345RightType Departmental Bulletin PaperTextversionpublisherKyoto UniversityBull. Inst. Chem. Res., Kyoto Univ., Vol. 68, No. 3, 1990      Base-Induced Cleavage of Sulfur-Sulfur Bond in Several                Disulfides Having a-Hydrogens            Shigeo TANIMOTO, Shigeo NOZAWA, and Yoshihiko  INOUE                               Received April 13, 1990    Several disulfides having a-hydrogens weredecomposed by lithium diisopropylamide (LDA) into the cor-responding thioaldehydes and thiolate anions. The thioaldehyde undergoes competitively one-electron transfer from LDA leading to a radical anion or nucleophilic attack by the thiolate anion simultaneously form-ed leading to a thiolate anion of hemidithioacetal. The radical anion was further converted to the correspon-ding thiolate anion by a hydrogen radical abstraction from solvent and/or the corresponding dithiolate dianion by dimerization.      KEY WORDS: Lithium diisopropylamide/ Benzyl phenyl disulfide/ 1,1'-                    [1,2-Bis(methylthio)-1,2-ethanediyl]bisbenzene/ 2,3-Ben-                   zodithian/ a,a'-Bis(methylthio)-o-xylene/ Dialkyl 2,2'                   dithiobisacetates/ Dialkyl 2, 3-bis(methylthio)butanedioates    In a recent paper') we reported that the lithium diisopropylamide (LDA)-induced fragmentation of dibenzyl disulfide at low temperature followed by the trapping with some alkyl halides afford 1,1"-[1,2-bis(alkylthio)-1,2-ethanediyl]bisbenzenes and alkyl a-alkylbenzyl sulfides. The reaction proceeds mainly via the fragmentation of a-carba-nion generated from dibenzyl disulfide into thiobenzaldehyde and a-toluenethiolate anion; the former thiobenzaldehyde is converted to a radical anion by one-electron transfer from LDA followed by alkylation-dimerization sequence providing 1,1'-[1,2-bis(alkylthio)-1,2-ethanediyl]bisbenzenes, and the latter a-toluenethiolate anion is con-verted to alkyl a-alkylbenzyl sulfide by alkylation-deprotonation-alkylation sequence. Twenty years ago, Hiskey and Dennis2) reported the potassium ethoxide-induced con-version of a,a -dithiobis(acetophenone) and of diethyl 2,2'-dithiobisacetate affoding 1,4-diphenyl- 1,4-butanedione-2,3-dithiol and diethyl 2, 2'-thiobisacetate-2-thiol, respective-ly. The reaction proceeds via the process involving sulfur-sulfur bond cleavage of a-car-banion generated from a, a'-dithiobis(acetophenone) or diethyl 2, 2'-dithiobisacetate pro-viding two intermediate fragments, the corresponding thiolate anion and thioaldehyde; these fragments combine leading to the final product with or without further deprotona-tion-rearrangement sequence. However, none of well-known disulfides, except three kinds of disulfides above-mentioned, has been submitted to such the base-induced fragmentation.    Thus, we have studied the LDA-inducced cleavage of sulfur-sulfur bond in some of easily available disulfides having a-hydrogens. In a few cases lithium 2,2,6,6-tetramethylpiperidide (LTMP) was used instead of LDA as the base. Initially, benzyl  * =Q-*A*, gf*, jthfitg. : Laboratory of Petroleum Chemistry, Institute for Chemical Research,   Kyoto University, Uji, Kyoto 611. (193)                               S. TANIMOTO, S. NOZAWA, and Y. INOUE           Table I. Base-Induced Fragmentation of Several Disulfides Having a-                 Hydrogens, Followed by Trapping with Methyl Iodide  Runa)Startingb) Base usedProductc) (yield/%)                    disulfide 1la LDA7a (26), 8 (57)        2la LDA+TMEDAd)7a (24), 8 (45)       3lb LDA5b (35), 7b (8), 8 (65)      4lc LDA7c (16), 8 (63)     5is LTMP8 (26)      6ld LDA5d (40), 8 (55)     7ld LTMP8 (53)       8le LDA5e (10), 7e (33), 8 (44)      9le LTMP7e (25), 8 (29)    109 LDA13 (55)    119 LTMP13 (21)     1214a LDA19a (24)     1314b LDA19b (26)     1414c LDA19c (19)     1514d LDA19d (22)     1614e LDA19e (18)          a) In all runs the presence of a few minor products was recognized by thin-layer              chromatography. These minor products, however, were not isolable by column             chromatography.          b) Besides 1, 9 and 14, benzyl t-butyl disulfide was allowed to react with LDA in            THF. This, with trapping with methyl iodide, afforded 25% yield of 7a together             with significant amounts of t-butyl methyl sulfide.          c) In all runs the unaltered disulfidescould not be recovered.          d) TMEDA: N, N, N, ^/-Tetramethylethylenediamine. TMEDA (0.30 g, 0.26            mmol) was added to the solution of LDA in THF prepared at the beginning.             Then, this mixture was used as the base under the sameconditions. phenyl disulfide (la) was treated with an excess of LDA in tetrahydrofuran (THF) at low temperature. This, with trapping with methyl iodide, led to 1,1'-[1,2-bis(methylthio)-1,2-ethanediyl]bisbenzene (7a) together with methyl phenyl sulfide (8). The results of analogous reactions usingp-substituted benzyl phenyl disulfides (ib, ic, id and le) as the starting disulfide as well as those using LTMP instead of LDA as the base are collected in Table I. As can be seen from Table I, LTMP is apparently un-suitable base for this kind of reaction; 25% yield of 4,4'-[1,2-bis(methylthio)-1,2-ethanediyl]bis(nitrobenzene) (7e) together with 8 was isolated in only Run 9. In Runs 1, 2, 3, 4, 6 and 8 either one of the compounds 5 and 7 or both were isolated together with significant amounts of 8. None of p-substituted benzaldehyde methyl phenyl dithioacetal or its related compounds was isoalted, meaning that there is no process in-volving the combination of intermediate thioaldehyde with benzenethiolate anion simultaneously formed. The process is probably minor one if it were. Thus, the reac-tion of 1 with LDA followed by trapping with methyl iodide seems to proceed as follows.    Next, 2,3-benzodithian (9) was submitted to the analogous base-induced fragmenta-tion at low temperature followed by trapping with methyl iodide. The product isolated (194)                                Based-Induced Cleavage of Sulfur-Sulfur Bond  R  O H2-S-S O                                  LDA                          ~ROCHS-SO—~-              (1) [RO  H=S +O (2) g O H=S R O CH-s      (2)(3)               HROH2-SCH3I 0 CH2-SCH3            (4)(5)                • O H-SOCH-SCH3                I CHI O H-S• O CH-SCH3 _   _            (6)(7) CH3Ia: R=Hd: R=CH30 s O --- CH3S 0 b: R=CH3 e: R=NO2 c: R=Br                       (8)        was a,a'-bis(methylthio)-o-xylene (13) alone (see Table I). The reaction seems to pro-       ceed via the process involving a-deprotonation, sulfur-sulfur bond cleavage giving o-       thioformyl-a-toluenethiolate anion 10, one-electron transfer from the base giving the        radical anion 11, hydrogen radical abstraction from THF as well as charge neutraliza-       tion by methyl iodide. None of 3-methylthio-1,3-dihydrobenzo[c]thiophene was        isolated. This means that there is no appreciable interaction between —CH2S- and the        thioformyl group of 10.           Lastly, several dialkyl 2,2'-dithiobisacetates (14) were allowed to react with LDA in THF followed by trapping with methyl iodide under the same conditions. The pro-      ducts isolated were dialkyl 2,3-bis(methylthio)butanedioates (19) alone. In all of Runs        12-16 none of alkyl (methylthio)acetates was isolated. This means that the initially        formed alkyl thioformylcarboxylate 15 and alkoxycarbonylmethylthiolate anion 16 com-       bine exclusively leading to the formation of intermediate species 17 which undergoes        deprotonation-rearrangement sequence to afford the dithiolate dianion 18. Thus, the         reaction seems to proceed as follows. (195)                             S. TANIMOTO, S. NOZAWA, and Y. INOUE    CICH       2~S BsaeCH~S~Segeh    CH2CH2CH2  ---J   (9)(10)   •:idh13 ••::::  22      (11)——(12) — (13)     ROCOCH2-S-S-CH2COORLDA- [RO OaHSSCH2COOR]           (14)                  Si-- ROCOCH=S + -S-CH2COOR1-----> ROCOCH-S-CH2COOR                                                                                                   -    (15) (16)(17) - S- -- S- S- -   -> ROCOCH-S-CHCOOR -------> ROCOCH-CHCOOR                                 (18)                SCH3 SCH3       CH3I ,ROCOCH---CHCOOR                                      a: R=CH3 d: R=i-C3H7                  (19) b: R=C2H5 e: R=n-C4H9 c: R=n-C3H7    In conclusion, a-lithiodisulfides, as unstable intermediates occurring in the reac-tion of disulfides having a-hydrogens with LDA, undergo fragmentation into thioaldehydes and thiolate anions. The thioaldehyde undergoes competitively one-elec-tron transfer from LDA leading to a radical anion or nucleophilic attack by the thiolate anion simultaneously formed leading to a thiolate anion of hemidithioacetal. The radical anion is further converted to the corresponding thiolate anion by a hydrogen radical abstraction from solvent and/or the corresponding dithiolate dianion by dimerization. On the other hand, the thiolate anion of hemidithioacetal undergoes deprotonation followed by intramolecular rearrangement leading to the corresponding dithiolate dianion if the deprotonation is possible. In our experiments, the thioaldehyde 2 or 10 underwent one-electron transfer by LDA, on the other hand, the thioaldehyde 15 underwent nucleophilic attack by the thiolate anion 16 simultaneously formed. This difference seems to be caused by the structural difference between these thioaldehydes, but with some uncertainty. (196)                         Based-Induced Cleavage of Sulfur-Sulfur Bond            Table II. 1H-NMR Spectral and Analytical Dataof Some. Products Obtained       Mp (°C) orFound (Calcd) (%) Compounda) Bp (°C/mmHg) 'H-NMR (S in CDC13)    (lit.)C H N      7a 98-100 (99.3-101)'r 1.78 (s, 6H), 4.03 (s, 2H), 6.8-7.4 69.74 6.55                     (m, 10H)(70.02) (6.61)      7b Not measured1.78 (s, 6H), 2.21 (s, 6H), 4.06 (s, 71.33 7.36                                2H), 7.0-7.2 (m, 8H)(71.47) (7.33)      7c Not measured1.82 (s, 6H), 4.05 (s, 2H), 6.9-7.4 44.49 3.60                   (m, 8H)(44.46) (3.73)      7e Not measured1.88 (s, 6H), 4.22 (s, 2H), 7.2-8.1 52.42 4.27 7.48                       (m, 8H)(52.73) (4.43) (7.69)      13 116/1.0-1.5 (114/1.0)s) 2.04 (s, 6H), 3.85 (s, 4H), 7.0-7.4 60.56 6.94                    (m, 4H)(60.55) (7.11)     19a 69-71 (71-72)9)2.19 (s, 6H), 3.60 (s, 2H), 3.79 (s, 40.18 5.98                6H)(40.32) (5.92)     19b Not measured1.31 (t, 6H), 2.20 (s, 6H), 3.57 (s, 44.87 6.80                           2H), 4.25 (q, 4H)(45.09) (6.81) •     19c Not measured0.97 (t, 6H), 1.6-1.8 (m, 4H), 2.20 48.80 7.66                              (s, 6H), 3.59 (s, 2H), 4.15 (t, 4H) (48.95)(7.53)     19d Not measured1.28 (d, 12H), 2.19 (s, 6H), 3.51 (s, 48.74 7.53                                2H), 5.0-5.2 (m, 2H)(48.95) (7.53)     19e Not measured0.93 (t, 6H), 1.3-1.5 (m, 4H), 1.6- 51.85 8.08                                1.7 (m, 4H), 2.19 (s, 6H), 3.57 (s, (52.14) (8.13)                             2H), 4.18 (t, 4H)   a) The compounds in Table II, except 13,are the mixture of stereoisomers.     Danehy and Parameswaran3) researched upon the decomposition of several disulfides in aqueous or nonaqueous solution. They reported that no one mechanistic scheme governs the alkaline cleavage of disulfides. Probably, half or more parts of the starting disulfides used in our experiments should be decomposed by LDA during the course of reaction leading to many compounds of low molecular weight which are solu-ble or insoluble in water. However, the process proposed by us seems to be the govern-ing one in the reaction of disulfides with base such as LDA although it compete with many other minor processes, none of which is definite.                             EXPERIMENTAL   Materials. The disulfides 1 were prepared by converting benzyl bromide or its p-substituted derivatives into the corresponding thiosulfates followed by treatment with sodium benzenethiolate4). 2,3-Benzodithian (9) was prepared by converting 1,2- bis(bromomethyl)benzene into the corresponding Bunte salt followed by treatment with one equivalent of iodine. The disulfides 14 were prepared as follows. Disodium (S-car-boxymethyl)thiosulfate, prepared from sodium chloroacetate and sodium thiosulfate, was converted by iodine and water into 2,2"-dithiobis(acetic acid). It was allowed to react with appropriate alcohols in the presence of p-toluenesulfonic acid5,6)    Base-Induced Fragmentation of Several Disulfides (1, 9 and 14) Followed by the Trapping with Methyl Iodide. General Procedure: A solution of LDA (or (197)                               S. TANIMOTO, S. NOZAWA, and Y. INOUE LTMP) in  THF was prepared by the well-known method using diisopropylamine (0.32 ml, 2.3 mmol) [or 2,2,6,6-tetramethylpiperidine (0.39 ml, 2.3 mmol)] in THF (6 ml) and 1.50 molar solution (1.47 ml, 2.2 mmol) of butyllithium in hexane. Only in Run 2, TMEDA (0.30 g, 2.6 mmol) was added to this solution of LDA in THF. To a stirred, cooled (-78°C) solution of 1, 9 or 14 (1.0 mmol) in THF (4 ml) was added, under nitrogen, the solution of LDA (or LTMP) in THF above-mentioned. After addi-tion, the reaction mixture was allowed to warm to —15°C and the stirring was con-tinued for 1 h at that temperature. The reaction mixture was cooled again to — 78°C and methyl iodide (0.47 g, 3.3 mmol) was added with stirring. The stirring was con-tinued for 1 h at —10- - — 5°C and then for 24 h at room temperature. The reaction mix-ture was quenched with .a saturated aqueous solution (20 ml) of ammonium chloride, and then extracted with ether (3 X 15 ml). The combined ethereal extract was washed with brine (20 ml), dried over magnesium sulfate and concentrated under reduced pressure to afford a residue, which was subjected to column chromatography on silica gel using 95% hexane-ethyl acetate as eluent.                             REFERENCES (1) H. Ikehira and S. Tanimoto, Bull. Chem. Soc. Jpn., 57, 1423 (1984). (2) R. G. Hiskey and A. J. Dennis, J. Org. Chem., 33, 563 (1968). (3) J. P. Danehy and K. N. Parameswaran, J. Org. Chem., 33, 568 (1968), and references cited therein. (4) H. B. Footner and S. Smiles, J. Chem. Soc., 127, 2887 (1925). (5) G. G. Stoner and G. Dougherty, J. Am. Chem. Soc., 63, 987 (1941). (6) T. C. Owen, J. M. Fayadh, and J. S. Chen, J. Org. Chem., 38, 937 (1973). (7) K.-H. Geiss, D. Seebach, and S. Seuring, Chem. Ber., 101, 1833 (1977). (8) D. W. Allen, P. N. Braunton, I. T. Millar, and J. C. Tebby, J. Chem. Soc (C), 3454 (1971). (9) M. Gerecke, E. A. H. Friedheim, and A. Brossi, Hela. Chim. Acta, 44, 955 (1961). 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Base-Induced Cleavage of Sulfur-Sulfur Bond in Several Disulfides Having α-Hydrogens

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Base-Induced Cleavage of Sulfur-Sulfur Bond in Several Disulfides Having α-Hydrogens

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