MAY1966
ACETOLYSIS O F BICYCLO [2.2.1IHEPT-2-ENE-Syn-7-METHYLC A T I O N
1577
The Questian of r-Electron Delocalization in the Bicyclo[2.2.l]hept-2-ene-syn7-methyl Cation. The Acetolysis of Bicyclo[2.2.1Jhept-2-ene-syn-and -anti-7methyl 2nd Bicyclo[2.2.l]heptane-7-methyl p-Bromobenzenesulfonates’ RUTAK. BLYAND ROBERT S. BLY Llepartment of Chemistry, University of South Carolina, Columbia, South Carolina 19108 Received October 16,1966 The acetollysis of bicyclo[2.2.l]hept-2-ene-syn-7-methylp-bromobenzenesulfonate is unaided by r-electron delocalization and exhibits considerable bimolecular character. At 115” it yields predominantly bicyclo [2.2 13hept-2-ene-syn-7-methyl acetate plus syn-7-methylbicyclo [2.2.1]hept-2-en-anti-7-y1acetate and a mixture of secondary acetates similar to those formed in the acetolyses of bicyclo[2.2.2]oct-5-en-mdo-2-y1arenesulfonates. p-bromobenzenesulfonate also exhibits some bimolecular The acetolysts of bicyclo [2.2.l]hept-2-en-anti-7-methyl character and at 115’ yields mostly bicyclo [2.2.l]hept-2-ene-anti-7-methyl acetate, some syn-7-methylbicyclo[2.2.1]hept-2-en-anti-7-y1 acetate, and a mixture of secondary acetates similar to those formed in the acetolyses of bicyclo [2.’2.2]oct-5-en-ezo-2-y1arenesulfonates. Under similar conditions the acetolysis of bicyclo [2.2.1]heptane-7-methyl p-bromobenzenesulfonate shows less bimolecular character than those of the unsaturated brosylates and yields bicyclo[2.2.1]heptane-7-methyl,7-methylbicyclo[2.2.l]hept-7-yl,bicycl0[2.2.2]oct-2-y1, and bicyclo[3.2.1]oct-ezo-2-yl acetates. At. 130’ the saturated brosylate is 2.35 times as reactive as the syn brosylate which is in turn 1.67 times more reactive than the anti brosylate. An explanation is offered to account for the nature and proportion of the products in each case.
Many examples of participation by A electrons of a nearby double bond in the rate-limiting step of a solvolysis reaction are known.2 The effect is potentially greater when the double bond is highly ~ t r a i n e d when ,~ the leaving group departs a primary ~ a r b o nwhen , ~ the double bond and the carbon carrying the leaving group are fixed in close proximity throughout the course of the reaction,5 and when the developing positive charge is disposed symmetrically with respect to both ends of the double bond.” In an effort to determine the effect of overlap geometry upon the extent of such Aelectron participation we have examined the solvolytic reactivity of the bicyclo[2.2.1Ihept-2-ene-7-alkyl brosylates (1) where n = 1 and 2. This series of compounds fulfills most of the desired conditions and offers the additional advantage of a leaving group which is bonded to a carbon of “normal” hybridization.’ We report here the syntheses and acetolyses of bicyclo [2.2.1]hept-2-ene-syn- and .-anti-7-methyl and bicyclo [2.2.1]heptane-7-methyl p-bromobenzenesulfonates, 2b, 3b, and 4b, respectively. (1) A preliminary report of this work was presented a t the 146th National Meeting of the American Chemical Society, Denver, Colo., Jan 1964; S b stracts, p 6C. (2) For recent summaries, see (a) J. A. Berson in “Molecular Rearrangements,” Part 1, P. deMayo. Ed.. Interscience Publishers, Inc., New York, N. Y.. 1963, p 111 ff; (b) B. Capon, Quart. Rev. (London), 18, 85 (1964). (3) (a) H.C. Brown in “The Transition State.” Special Publication No. 16, The Chemical Society, London, 1962, p 140 ff; (b) H. C. Brown and S. Nishida, Abstracts of the 139th National Meeting of the American Chemical Society, St. Louis, Mo., March 1961, p 20; cf. (c) 8. Winstein, M. Shatavsky, C. Norton, and R. B. Woodward, J . A m . Chem. Soc., 77, 4183 (1955); (d) S. Winstein and C. Ordronneau, ibid., 81, 2084 (1960); (e) unpublished work of H. ;I. Schmid and K. C. Schreiber, reported by 5. Winstein and M. Shatavsky. tbid., 78,595 (1956). (4) Provided t h a t nucleophilic participation b y the solvent is held to a minimum, e.g. (a) 6. Winstein, C. R. Lindgren, H. Marshall, and L. L. Ingraham, ibid., 76, 147 (1953); (h) S. Winstein and H. Marshall, ibid., 74, 1120 (1952); (c) P. D. Bartlett, S. Bank, R. J. Crawford, and G. H. Schmid, ibid., 87, 1288 (1965). (5) Cf. (a) R. G. Lawton, ibid., 83, 2399 (1961); (b) P. D. Bartlett and S. Bank, ibid., 88. 2591 (1961); (c) 8. Winstein, B. K. Morse, E. Grunwald, H. W . Jones, J. Corse, D. Trifan, and H. Marshall, ibid., 74, 1127 (1952); (d) P. D.Bartlett, W. S. Tlphanovsky. D. A. Bolon, and G. H. Schmid, ibid., 87, 1288 (1965). (6) (a) P. D. Bartlett and D. G. Sargent, ibid., 87, 1297 (1965); (b) P. Bruck, D. Thompson, and S. Winstein, Chem. Ind. (London), 590 (1960); ( 0 ) S. Winstein and R. L. Hansen, Tetrahedron Letter#. No. 26, 4 (1960). (7) (a) H. C . Brown and FI. M. Bell, J . A m . Chem. SOC.,86, 2324 (1963); see also (b) R. C. Fort, Jr., and P. Schleyer, Chem. Rev., 64, 277 (1964), for a discussion of this point.
1
2
a, Z = OH b, Z = OBs c, Z = OAc
4
3 d, Z = OTs e, Z = NH2
Results Kinetics.-The apparent first-order titrimetric rate constants, k (see Experimental Section), for the solvolysis of Zb, 3b, and 4b in anhydrous acetic acid containing about 1% acetic anhydride are recorded in Table I. The dependence of the rate of each acetolysis upon added sodium acetate, sodium brosylate, and lithium perchlorate-expressed by the parameters bn in the equation8 k
=
ko(1
+ bl[salt 1 ] i + bZ[salt 211)
where ko is the apparent first-order titrimetric rate constant at zero ionic strength and the subscript i H -CHzOBs
H-CHaZ HOAc-NaOAc 115”
2b
2c
+
unknown acetate
+
il 8c
7c
!iC
1oc
9c
a , Z = OH b, Z = OBs C, 2 = OAc
llc
d, Z = OTs e , Z = NH2
(8) A. H. Fainberg and 9. Winstein, J . A m . Chem. SOC.,78, 2763 (1956).
BLYAND BLY
1578 TABLEI APPARENT FIRST-ORDER RATECONSTANTS FOR 2 BROSYLA TES OF THE BICYCLI( Run
Compd
Temp, OC
[ROBsli, M
THE
[NaOAo]i ,
M
Pi
ACETOLYSIS
stands for initial concentration-are given in Table 11. The derived activation parameters for the acetolysis of each brosylate (see Experimental Section) are listed in Table 111. TABLE I1 OF APPARENT FIRST-ORDERACETOLYSIS DEPENDENCE RATESAT 129.7' UPON ADDEDSALTS Compd
2b 3b
4b
10%
aec-1
2.65 1.59 6.21
8.74 15.2 5.45
of b for addedNaOBs LiC104
2.03 4.54 3.16
TABLEI11 ACTIVATION PARAMETERS FOR THE ACETOLYSIS OF THE BICYCLIC BROSYLATES
106 k, sec -1
99.4 0.0215 0.0299 0.0312 0.175 2b 1 0.0216 0.0309 0.0322 0.195 2 0.0216 0.0296 0.0309 0.198 3 115.0 0.0212 0.0295 0.0313 0.873 4 0.0212 0.0290 0.0308 0.874 5 115.2 0.0412 0.0852 0.0906 1.29 6 129.7 0.0207 0,0295 0.0917" 4.29" 7 0.0208 0.0642 0 . 0947b 4,266 8 0.0206 0.0876 0.0949 4.65 9 0.0425 0.0849 0.0920 4.57 10 0.0208 0.0558 0.0605 3.98 11 0.0209 0.0295 0.0320 3.30 12 0,0207 0.0292 0.0317 3.32 13 99.4 0.0217 0.0300 0.0313 0.153 14 3b 0,0216 0.0311 0.0324 0.156 15 0.0215 0.0297 0.0310 0.140 16 115.0 0.0204 0.0296 0.0315 0.638 17 0.0212 0.0295 0.0314 0.651 18 115.4 0.0430 0.0839 0.0893 0.971 19 129.7 0.0207 0.0295 0.0931" 3.16c 20 0.0209 0.0635 0. 0936d 3.2gd 21 0.0208 0.0851 0.0922 3.68 22 0.0435 0.0846 0.0917 3.54 23 0,0207 0.0556 0.0602 2.95 24 0.0207 0.0299 0.0324 2.35 25 0.0206 0.0294 0.0319 2.33 26 99.4 0.0213 0,0300 0.0313 0.412 4b 27 0,0214 0.0311 0.0324 0.410 28 0,0214 0.0302 0.0315 0.403 29 115.0 0.0209 0.0292 0.0310 1.82 30 0.0209 0.0293 0.0311 1.92 31 115.2 0.0371 0.0856 0,0910 2.51 32 129.7 0.0205 0.0296 0.0929' 10.88" 33 0.0208 0.0637 0.0940' 8.82, 34 0.0400 0.0858 0.0930 9.02 35 0.0204 0.0842 0.0912 9.03 36 0.0205 0.0560 0.0607 8.15 37 0.0205 0.0292 0.0317 7.28 38 0.0206 0.0293 0.0318 7.11 39 0.0226 0.0255 0.0276 7.00 40 0.0200 0.0251 0.0280 7.11 41 b Contains 0.0232 a Contains 0.0551 M lithium perchlorate. M sodium p-bromobenzenesulfonate. c Contains 0.0564 M lithium perchlorate. d Contains 0.0229 M sodium p-bromobenzenesulfonate. Contains 0.0561 M lithium perchlorate. Contains 0.0231 M sodium p-bromobenzenesulfonate.
-Value NaOAo
VOL.31
6.55
9.54 10.5
Products.-The acetolysis of bicyclo [2.2.1 Ihept-2ene-syn-7-methyl p-bromobenzenesulfonate (2b) a t 115" (eq 1) yields a mixture which contains-in addition to a small amount of hydrocarbon (@--the unrearranged acetate 2 c, syn-7-met hy lbicy clo [2.2.1 ]hept-2-en-anti-
AH*, Compd
kcal/mole
BicycloI2.2.1J hepb2-en~yn-7methyl OBs (2b) Bicyclo [2.2.1]hepb2-ene-unti-7methyl OBs (3b) Bicyclo [2.2.1]heptane-7-methyl OBs (4b)
AS*, eu
27.0 i 0 . 2 -12.6 It 0 . 5 26.3 =I=0 . 2
-15.0 It 0 . 5
27.4 i 0 . 2
-10.1 f 0 . 5
7-yl acetate (Sc), tricyclo [2.2.1.02~6]heptane-3-methyI acetate (Sc), bicyclo [3.2.1Ioct-3-en-endo-2-yl acetate (~OC), bicyclo [3.2.l]oct-3-en-ezo-2-ylacetate (1 IC), bicyclo [2.2.2]oct-5-en-ezo-2-yl acetate (7c), an unidentified acetate 8c (see Experimental Section), and a t least four diacetates. The acetolysis mixture from 2b contains no detectable amount (ie., more than -0.1%) of bicyclo [2.2.1Ihept-2-ene-anti-7-methyl acetate (3c), tricyclo [2.2.2.02~6]oct-endo-3-yl acetate (12c), tricyclo[2.2.2.02!6]oct-ez0-3-yl acetate (13c),or bicyclo [2.2.2]oct5-en-endo-2-yl acetate (SC).~The relative proportion
6
Z
12
Z = OH b, Z = OBs a,
c, Z = OAc
13
d, Z = OTs e, 2 = NH2
of the various acetates in the acetolysis mixture, determined as described in the Experimental Section, is recorded in Table IV. TABLE IV COMPOSITION OF THE ACETOLYSIS MIXTUREOF BICYCLO[2.2.1] HEPT-2-ENE-Syn-7-METliYL p-BROMOBENZENESULFONATE (2b) AT 115' IN BUFFERED ACETIC ACID % composition* a t Compd5
0.42 half-lifec
1.02 half-livead
9.0 half-lives
*
0 . 6 =!= 0 . 2 0 . 6 0.2 86.5Al.O 78.5Al.O 0 . 5 f 0.2 0 . 5 f0 . 2 8C 1 . 2 f0 . 3 1 . 2 =k 0 . 3 9c -0.2 0.8A 0.4 1oc 3 . 0 It 0 . 5 2 . 8 =!= 0 . 5 llc 7 . 5 i~0 . 5 7.6 A 0 . 5 Diacetates ... -0.5 8 . 0 f0 . 5 In order of elution from the 20-ft Carbowax column. Excluding hydrocarbon(s). c 79% of the starting brosylate, 2b, uncontaminated with isomeric brosylates, waa recoverd from the reaction mixture. d 48% of the starting brosylate, 2b, uncontaminated with isomeric brosylates, waa recovered from this reaction mixture. 5c 2c 7c
0.6 i0.2 87.211.0 0.4 f0.2 1 . 2 j= 0 . 3 CHH). Anal. Calcd for C14HlaBrOsS:C, 48.99; H , 4.41; Br, 23.28; 0,13.98. Found: C,49.04; H,4.55; Br,23.39; 0,13.96. This material was used for the acetolysis studies without further purification. Bicyclo[Z.2.l]hept-2-ene-syn-7-methylAcetate (2c).-A solution of 50 mg (0.40 mmole) of bicyclo[2.2.l]hept-2-ene-8yn-7methanol (2a) and 0.5 ml of acetic anhydride in 1.0ml of pyridine was heated under reflux for 12 hr. The reaction mixture was cooled to loo, acidified to pH -5, and extracted with four 5-ml portions of pentane. The combined pentane extract was washed (41) Melting and boiling points are uncorrected. Microanalyses were performed by either Bernhardt Mikroanalitisches Laboratorium, Mtilheim, or Galbraith Laboratories, Inc., Knoxville, Tenn. The infrared spectra were determined on a Perkin-Elmer grating spectrophotometer, Model 337, the nmr spectra on a Varian A-80 spectrometer at -35O using tetramethylsilane ( T 10.00) and/or chloroform ( T 2.69) as internal standards in carbon tetrachloride. The gas chromatographic analyses were carried out on an F and M Model 500 linear temperature-programmed gas chromatograph using helium as a carrier gas at flow rates of 50-120 cc/min. The chromatographic columns used were 0.25 in. X 8 f t coiled copper tubes packed with 20% Carbowax 20M on 100-140 mesh Gee-Chrom-S (Applied Science Laboratories, Inc., State College, Pa.) or 20% Silicone Oil 200 on 60-80 mesh Chromasorb I' (Johns-Manville Products Corp.); a 0.25 in. X 7.5 ft coiled copper tube packed with 20% Carbowax 20M on 60-80 mesh Chromasorb W ; and a 0.25 in. x 20 ft coiled copper tube packed with 20% Carbowax 20M on 1OC-140 mesh Gas-Chrom-S. (42) R. K. Bly and R. S. Bly, J . U r p . Chem., 18,3165 (1963). (43) R. S. Tipson, ibid., 9, 235 (1944).
VOL.31
with water and dried over anhydrous sodium sulfate. The solvent was removed by distillation through a 0.5 x 15 cm wirespiral-packed column. The residue was dktilled in a short-path still at 5 mm, using an oil-bath temperature of 115', to give 51 mg (77%) of product: 3070, 1620, 716 (-HC=CH-), 1740, and 1234 cm-l (-0-COCHa); nmr, v::? T 4.16 (quintet, 2 =CH-),42b44 6.13 (doublet, J = 7 cps, 2 -0-CH2CHCHH). Anal. Calcd for ClOHl4O2: C, 72.26; H , 8.49. Found: C, 72.40; H, 8.66. Bicyclo[2.2.1]hept-2-ene-anti-7-methyl p-Bromobenzenesulfonate (3b).-This compound was prepared in the same manner as the syn isomer 2b,'s using 4.02 g (0.0324mole) of bicyclo[2.2.l]hept-2-ene-anti-7-methanol(3a),L28.86 g (0.0347 mole) of p-bromobensenesulfonyl chloride, and 40 ml of pyridine. The yield was 8.86 g (79.6%): mp 83-84'; 3090, 3060, 1640,700(-HC=CH-), 1360,and 1280 cm-l (-OSO,); mmr, v::? T 2.32 (singlet, 4 =CH-, aromatic), 3.99 (triplet, J = 2.3 cps, 2 =CH--, n o n a r ~ m a t i c ) , ~ 6.29 , ~ ' (doublet, J = 8 cps, 2 -O-CH&HCHH, and 2 >CHH). Anal. Calcd for C14HlaBrOaS:C, 48.99; H , 4.41; Br, 23.28. Found: C, 49.18; H, 4.33; Br, 23.34. This material was used for the acetolysis studies without further purification. Bicyclo[2.2.l]hept-2-ene-unti-7-methyl Acetate (3c).-This compound was prepared in the same manner as 212, using 11 mg (0.089mmole) of bicyclo [2.2.l]hept-2-ene-unti-7-methanol (3a), 0.5 ml of acetic anh dride, and 1 ml of pyridine. The yield was 8.0 mg (55%): 3070, 1610,c7'?0 (-HC=CH-), 1750, and 1242 cm-l (-0-COCHs); nmr, vmsX T 3.96 (triplet, J = 2 cps, 2 =CH-),4n,44 6.38 (doublet, J = 8 cps, 2 -O-CH&HCHH, and 2XHH). Anal. Calcd for C10H1402: C, 72.26; H , 8.49. Found: C,
VZ?
::v
v::!
72.23; H, 8.60. Bicyclo[2.2.l]heptane-7-methanol(4a).-TO a solution of 1.00 g (8.06mmoles) of bicyclo[2.2.1] hept-2-ene-syn-7-methanol (2a) in 15 ml of absolute methanol was added 200 mg of 5% palladiumon-charcoal catalyst. The solution was stirred in an atmosphere of hydrogen until no more gas was taken up. The methanol WBS removed by distillation a t atmospheric pressure and the product was distilled under vacuum in a short-path still (oil-bath temperature, 90-100",pressure, 7 mm) to yield 0.99 g (97%) of the saturated alcohol 4a: YE: 3640 (0-H, nonbonded) and 3350 cm-l (broad, 0-H, bonded); nmr, v::? T 6.52 (doublet, J = 8 cps, 2 -O-CH2CH CeH6 > p-N02C6H4).s This is easily seen from the first three reaction times recorded in Table I. The 1)-nitrophenacyl ylid 2c required 10 (1) Paper XI: A. J. Speziale and K. W. Ratts, J. Am. Ckern. SOC., 87, 5603 (1965). (2) (a) H. Staudinser and J. Meyer. Helu. Chim. Acta. 4, 635 11919); (b) J. E. Franz and C. Osuch, Tetrahedron Letters, 18, 841 (1963). (3) 0.Dimroth, Chem. Ber., 88, 670 (1905). (4) A. M. van Leusen, P. M. Smid, and J. Strating, T e h h e d r o n Letters, 6,337 (1965). (5) For discussions of :vlid basicities. see (a) A. J. Speziale and K. I\’, Ratte, J . Am. Chem. Soc., 86, 2790 (1963); (b) 5. Fliszrr, R. F. Hudson, and G. Salvadori, H e h . Chim. Acta, 48, 1580 (1963).
hr (infrared monitor) with tosyl azide to obtain the triazole 4c; the acetonyl ylid 2a required only 15 min for complete conversion to triazole 4a. These observations are in accord with the reported basicities of the ylidse5 CHARTI1
5
The adduct from tosyl azide (5,R’= p-CH&sH8Oz-; see Chart 11) can delocalize the electron pair via p-d overlap with the sulfonyl group thus diminishing the reversibility of the reaction. Similar resonance stabilization is possible in the adduct from benzoyl azide. However, when R’ is alkyl, e.g., 3c, or aryl, 3d, no such
