246 J.C.S. Perkin IFree-radical Reactions of Halogenated Bridged Polycyclic Compounds.Part XVI. t Addition of Methanethiol and I ,I -Dirnethylethanethiol to5-su bstituted 1,2,3,4,7,7- HexachloronorbornadienesBy D. R. Adams and D. 1. Davies,” Department of Chemistry, King‘s College, Strand, London WC2R 2LSThe attack of alkylthio-radicals on a 5-substituted 1,2,3,4,7,7-hexachloronorbornadiene affords the 5-substituted6-endo-alkylthio-I ,2,3,4,7,7-hexachloronorborn-2-en-5-yl radical, which may undergo chain transfer from eitherthe exo- or the endo-direction to afford a 5-endo (or 5-exo)-substituted 6-endo-alkylthio-l,2,3,4,7,7-hexachloro-norborn-2-ene. Alternatively the radical can rearrange to the 4-substituted 7-syn-alkylthio-I ,2,3,5,6,6-hexa-c h I o ro n o rb o r n - 2 -en - 5 - y I ra di ca I, which on chain transfer affords the 4- substituted 7 -syn - a I ky I t h i o - 1 ,2,3,5 - endo, -6.6-hexachloronorborn-2-ene. Product proportions depend on the nature of the 5-substituent in the diene, andmay be rationalised in terms of the possible structure of the first-formed radical, and of interactions between the5-substituent and the alkylthio-group in this radical.The major product from reaction of an alkanethiol with5-chloromethyl-l,2,3,4,7,7- hexachloronorbornadiene i s a 1.4.5.6.7.7- hexachloro-3-methylenenorborn-5-en-2-endo-yl alkyl sulphide.THE major products formed in the addition of alkane-thiols to hexachloronorbornadiene (Ia) are alkyl1,4,5,6,7,7-hexachloronorborn-5-en-2-endo-yl sulphides(3a) and alkyl 1,2,3,5-elzdo,6,6-hexachloronorborn-2-en-7-syn-yl sulphides (7a) in the approximate ratio of 1 : 2(R = Me or Et).l Both these products are derived byattack of thiyl radicals from the elzdo-direction to givethe intermediate radical (2).This radical (2) eitheraffords (7) on chain transfer. The driving force for therearrangement was considered2 to be the formation ofa chlorine-stabilised radical.s It was of interest tostudy the addition of thiols to some 5-substitutedhexachloronorbornadienes (1b-e) to discover the effectof the substituent on (i) the direction of chain transfer ofintermediate (2), and (ii) the ease of rearrangement ofintermediate (2) to intermediate (6). The proportionst Part XV, R. Alexander and D. I. Davies, J.C.S.Perkin ?, A. N. Nesmeyanov, R. Kh.*Friedlina, V. N. Kost, and%. Ya.1973, 83. Khorlina, Tetrahedron, 1961, 16, 941974 241of the products (3), (4), and (7) formed in the additionof methanethiol and of 1,l-dimethylethanethiol to thedienes (1b-e) are recorded in the Table, which alsoincludes, for comparison purposes, the proportions of(3a) or (4a) and (7a) formed in the respective additionsof methanethiol and ethanethiol to hexachloro-norbornadiene (Ia) .Studies on homolytic aromatic substitution * suggestthat all types of substituent, in the absence of stericRS- - C1Xt 11ClCla ; X = H (51b; X = Phc ; X = Med; X = C1e; X = C0,McRSH__c27to stabilise the radical centre in (2c), resulting in readyrearrangement of (2c) to (6c), or the structure of theradical centre is such that chain transfer is precluded sothat rearrangement to (6c) is the only possible course ofreaction.suggests that substitutedradicals (2) will be pyramidal, and the two possiblequasitetrahedral structures are (8) and (9).In theabsence of electrostatic interactions between groups XThe available evidence+C l gjRXRSH - H c$;l xClC l(61Products and conditions for thiol addition to 5-substituted hexachloronorbornadienesProduct proportions (%)r A Method ofDiene x Thiol time (h) Reaction !3) I (4) , ( 7 7 analysis tMeSH 48 75 31 69 N. m. r. :;;; : $ EtSH 48 65 31 69 X.m.r.(lb) Ph MeSH 120 100 88 0 12 N. in. r.100 0 0 N.1n.r.0 0 100 N.m.r.-G.1.c. (a)0 0 100 N.m.r.-G.1.c.(a)61 25 14 N.m.r.-G.1.c. (a)(lc) Me MeSH 48(lc) Me ButSH 72(Id) Cl ButSH 48 60 47 6 47 N.m.r.-G.1.c. (a)(le) C0,Me MeSH 48 100 100 0 0 N.m.r.-G.1.c. (b)(le) C0,Me ButSH 48 100 100 0 0 N.m.r.4.l.c. (b)t G.1.c. analysis was carried out at 100-180" on a Perkin-Elmer F 11 gas chromatograph fitted with a 2 m x & in stainless steelcolumn packed with (a) 6% Apiezon L on AW-DMCS Chromosorb W (80-100 mesh) or (b) 2.6% Silicone gum rubber E 301 onAW-DMCS Chromosorb W (80-100 mesh).Reaction yo(lb) Ph ButSH 48 72 t(Id) C1 MeSH 48 98 :;$ Product contains ca. 20% of an unidentified compound.effects, stabilise free radicals. This leads to the expect-ation that a radical (2b-e) with a 5-substituent shouldbe more stable than the radical (2a) (X = H), and henceand SR, structure (9) should be the most favouredbecause the unfavourable eclipsing of these groups inless formation prone of to product rearrange (7). to This radical expectation (6) leading is realised to the c:q:R c : .; when X = Ph, C1, or CO,Me, but not when X = Methe rearranged product (7c). This anomalous resultwhen X = Me implies that either the methyl group failsD. H. Hey, Adv. Free Radical Chem., 1967, 2, 47; D. I.Davies, D. H. Hey, and €3. Summers, J . Cham. Soc. (C), 1971,2681.D. I. Davies and P. Mason, J . Chem. Soc. (C), 1971, 288.(Table), since the addition of thiols to (Ic) affords solely c1 CI CIx(81 (91(8) is absent. Since both Me and SR are electron-donating @Oups, they exert a repu1sive inter-action on each other when eclipsed as in (8c); thi248 J.C.S.Perkin Ifurther favours (9c) over (8c). In the favoured inter-mediate (Sc), overlap of the orbital at the radical centrewith the x-electron orbitals of the chlorine-substituteddouble bond occurs, which allows the ready rearrange-ment of (2c) to (6c) to be rationalised. Studies onhomolytic aromatic substitution * predict similar stabilis-ation of radical centres by C1 and Me; therefore thedifference between (2c) and (2d) will be the relativeimportance of (8) and (9) when X is C1 and Me, re-spectively. The formation of appreciable quantities of(3d), derived from (2d), shows that in spite of theeclipsing of C1 and SR, appreciable amounts of productare derived from (8d).A possible explanation is thatthe attraction between groups of opposite inductiveeffect reduces the steric disadvantage occasioned by theeclipsing of C1 and SR. The importance of (8d) relativeto (9d) decreases as the size of SR increases from SMeto SBut. Intermediate (9d) leads to products (4d) and(7d). Chain transfer of (9d) with thiol becomes stericallymore difficult as the size of the thiol is increased andhence rearrangement to (6d) and formation of (7d) isfavoured with ButSH.With X = Ph very little rearrangement of (2b) to(6b), and hence formation of (7b), occurs. WithX = CO,Me, no rearrangement of (2e) occurs at all and(3e), derived by chain transfer of (2e) with thiol, is thesole product. On the assumption of pyramidal inter-mediates this indicates that for these groups (8) shouldbe favoured entirely over (9) which seems improbableon account of the size of the C0,Me and Ph groups andtheir consequent unfavourable steric interaction withan SR group.Since the groups C0,Me and Ph areHunsaturated, radical structures (2b) and (2e) are unlikelyto be pyramidal as in (8) and (9), and probably havecontributions from structures like (10) and (11). Suchstabilisation effectively prevents interaction with thechlorine-substituted double bond, and consequent re-arrangement. Examination of models, bearing in mindthe well-known preference for exo chain transfer 2,6 intwo-stage additions to norbornene-type double bonds,rationalises exclusive exo chain transfer from the planarradicals (2b) and (2e).The reaction of the chloromethyl diene (12) with theH.C. Brown and J. H. Kawakami, J . Amev. Chem. SOC.,1970, 92, 201, 1990; H. C. Brown and Kwang-Ting Liu, ibid., p.3502; H. C. Brown, J. H. Kawakami, and S. Ikegami, ibid., p.6914.R. Alexander and D. I. Davies, J . Chem. SOC. (C), 1971, 6 . * J. C . Davis, jun., andT. V. Van Auken, J . Amer. Chem. SOG.,1966, 87, 3900; P. Laszlo and P. von R. Schleyer; ibid., 1964, 86,1171.two alkanethiols did not lead to the 1 : 1 adducts (3),(a), and (7) (X = CH,Cl). The only identifiable productfrom the reaction with methanethiol was the methylf % RSHC l \,a CI, ,CI(151 (16 1hexachloromethylenenorbornen-2-ertdo-yl sulphide (14 ;R = Me), which was characterised by oxidation to asulphone.The reaction with 1 ,l-dimethylethanethiolgave, in low yield, the corresponding t-butyl sulphide(14; R = But), which was identified on the basis of itsn.m.r. spectrum.The formation of (14) is unlikely to involve additionof ail alkylthio-radical to (12) to give the intermediate(13), which then loses a chlorine atom. Alternativeroutes such as (i) allylic rearrangement of (12) to (15)(control experiments show that this occurs less readilythan with the corresponding bromides ') followed bynucleophilic substitution or (ii) chain transfer of (13) toafford (16) followed by loss of hydrogen chloride, areunlikely since neither (15) nor (16) could be detected asa reaction intermediate.All new products reported in this paper were identifiedon the basis of their n.m.r.spectra, which were con-sistent with those reported for norbornenes s andchlorine-substituted norbornen~s.~.EXPERIMENTALThe following compounds were prepared by literaturemethods : 1,2,3,4,7,7-hexachloro-5-phenylnorborna-2,5-diene ( lb) ,lo 1,2,3,4,5,7,7-heptachloronorborna-2,5-diene(ld),ll methyl 1,4,5,6,7,7-hexach1oronorborna-2,5-diene-2-carboxylate (le).l21,2,3,4,7,7-Hexachloro-5-methylnorbo~na-2,5-d~ene (lc).-Hexachlorocyclopentadiene (10.0 g, 0.04 mol) and prop-1-yne (4.0 g, 0.1 mol) were heated at 180" for 7 h in a Cariustube sealed under nitrogen. The tube was cooled, opened,and the excess of prop-l-yne allowed to evaporate. Dis-tillation of the residue afforded the diene (lc) (11.1 g),9 K.L. Williamson, J . Amer. Chem. SOL, 1963, 85. 616; K. L.Williamson, N. C . Jacobus, and K. T. Soucy, ibid., 1964,86,4021;K. L. Williamson, ibid., p. 6712.l o A. J. Fry, J . Org. Chem., 1966, 31, 1863.l1 M. J. Parrott, Ph.D. Thesis, London, 1971; C. H. M. Adams,K. Mackenzie, and P. R. Young, J.C.S. Perkin II, 1972, 1856.l2 D. I. Davies, P. Mason, and M. J. Parrott, J . Chem. SOC. (C),1971, 34281974b.p. 50" at 0.01 nimHg, nD25 1.5460 (lit.,13 1.5440) (Found:C, 30.9; H, 1.4. Calc. for C,H,Cl,: C, 30-7; HI 1.3%),T (60 MHz) 3-70 (9, H-6) and 8.03 (d, CH,), J(6,CH3)2.2 Hz, vmX. 1600s (cis-ClC=CCl) and 1635m cm-l (cis-MeC=CH) .5-Chloronzethyl- 1,2,3,4,7,7-hexachloronorborna-2,5-diene(12) .-Hexachlorocyclopentadiene (22.0 g, 0.08 mol) andprop-2-ynyl chloride (18.0 g, 0.24 mol) were heated a t 135"for 24 h in a Carius tube sealed under nitrogen.The tubewas opened and the product mixture distilled to affordsuccessively: prop-2-ynyl chloride (3.5 g), b.p. 45" a t20 mmHg; a mixture (15.3 g), b.p. 90-96" a t 0.3 mmHg ofhexachlorocyclopentadiene and the diene (12) ; and thediene (12) (11-7 g), nD25 1.5640, b.p. 74" a t 0.01 mmHg(Found: C, 27.9; H, 1.0. C,H3C1, requires C, 27.7; H,0.9%), 7 (60 MHz) 3.35 (t, H-6) and 5.73 (d, CH,Cl),J(6,CH2C1) 1.5 Hz, vmr. 1603s (cis-ClC--CCl) and 1630m cm-lAddition of -Wethanethiol and 1,l-Diunethylethanethiol to5-Sztbstituted Hexachlo~onorborna-2,5-dienes (lb-e) .-Thediene (0.003 mol) and excess of thiol (0.015 mol) weremixed, azobisisobutyronitrile (0-1 g) was added, and themixture was heated a t 60" in a sealed tube.Wherenecessary further amounts (0.1 g) of initiator were addedevery 2 days. When the reaction was largely complete,the tube was opened and the excess of thiol allowed toevaporate. The crude product was analysed for productproportions by g.1.c. (Table) and product structures werededuced from the n.m.r. spectrum of the mixture, whichalso allowed a check on product portions. Single productswere purified by recrystallisation from methanol ; wherepossible mixtures were separated by column chroniato-graphy. N.m.r. and i.r. data and analyses and propertiesof products are available as Supplementary PublicationNo. SUP 20895 (3 pp.)* Control experiments showed thatproduct proportions did not vary during the course of thereaction.Reaction of ilfethanethiol with 5-Chloromethylhexachloro-norborizadiene (12).-The diene (12) (1.0 g, 0-0029 rnol), anexcess of methanethiol (1.0 g , 0.02 rnol), and azobisiso-butyronitrile (0-1 g) were mixed and the mixture washeated a t 60" in a sealed tube for 84 h.The tube was thencooled and opened, and the excess of thiol allowed toevaporate. G.1.c. of the residue on column (a) (see Table)showed that it consisted of unchanged diene (12) and one(c~s-C~CH~*C=CH).* For details of Supplementary Publications, see Notice toAuthors So. 7 i n J . C h i n . SOC. (A4), 1970, Index Issue.major product believed to be 1,4,5,6,7,7-hexachloro-3-methylenenorborn-5-en-2-endo-yl methyl sulphide (14 ; R =Me), T 4.21 (m) and 4.43 (m) (=CH,) and 7.71 (s, SCH,).The reaction mixture (0.5 g) in methanol ( 5 ml) was stirredfor 24 h with a solution of hydrogen peroxide (30 w/v ; 2 ml)containing ammonium molybdate (0.1 g).The mixturewas then poured into water (20 ml) and extracted withether (3 x 20 ml); the extract was washed with ferroussulphate solution (2 x 20 ml) and water (2 x 20 ml), dried(MgSO,), and evaporated. The residue was chromato-graphed on silica gel (B.D.H. 60-120 mesh) with lightpetroleum (b.p. 40-60") and mixtures of light petroleumand ether as eluants to afford, successively, unchangeddiene (12) (0.2 g) and 1,4,5,6,7,7-hexachloro-3-nzethylene-norborn-5-en-2-endo-yZ methyl sulphone (0.1 g), b.p. 97-98"(Found: C, 27.2; H, 1.6.C,H,Cl,SO, requires C, 27.7;H, 1-5%), T (60 MHz) 3.89 (t, H-8 transoid), 4.09 (9, H-8cisoid), 5.47 (t, H-6-exo), and 7.00 (s, SO,*CH,), J ( 8 -transoidI8-cisoid) 1.3, J(8-transoid,B-exo) 1-7, J(8-cisoid,6-exo) 1.5 Hz, vmx 1603 (cis-ClC=CCl), 1145, and1330 cm-l (SO,).Reaction of 1,l-Diirtethylethanethiol with 5-Chlorornethyl-hexachloronorbornadiene (1 2) .-The diene (1 2) ( 1 g, 0.002 9mol), an excess of thiol (1.8 g, 0.02 mol), and azobisiso-butyronitrile (0.1 g) were mixed and heated a t 60" in asealed tube for 77 h. The tube was then cooled andopened, and excess of thiol allowed to evaporate. G.1.c.analysis of the residue on column (a) (see Table) showed i tto consist of unchanged diene (12) and one major com-ponent. Chromatography on silica gel (Fisons 100-200mesh) with light petroleum (b.p. 40-60") as eluant affordedunchanged diene (12) (0.05 g), a mixture (0-3 g) of un-changed diene (12) and product (14; R = But), and crude1,4,5,6,7,7-hexachloro-3-methylenenorborn-5-en-2-endo-yl t-butyl sulphide (14; R = But) (0.2 g), b.p. 90" a t 0.05mmHg, T (60 MHz) 4.30 (H-8 transoid), 4.47 (H-8 cisoid),5.92 (t, H-6-exo), and 8-58 (s, But), J(8-cisoid,8-transoid)1, J(8-transoid,G-exo) 1.8, J(8-cisoid,6-exo) 2.1 Hz, vmax.1598 cm-l (cis-ClC=CCl). Attempts to characterise thesulphide via oxidation to a sulphone led to decomposition.D. R. Adams thanks the S.R.C. for a Research Student-ship.[3/1585 Received, 26th Jzdy, 19731l3 D. Seyferth and A . B. Envin, J . L 4 ~ i i e v . Chew. Soc., 1967, 89,1458