Secondary 2‐Norbornyl Cation Intermediates Substituted at C(5) and C(7) by Electron‐withdrawing Groups. Addition of fluorosulfuric acid to unsaturated norbornane derivatives

Abstract

SummaryLow temperature (-130" to -110") addition of exo-norborn-5-en-2-01 (7) to excess HS03F in S02CIF yielded a mixture of exo-5-(fluorosulfonyloxy)-exo-2-and endo-2-norbornylhydroxonium ions (9 + 10) under kinetic control that was different from the mixture of 9 + 10 obtained by addition of endo-norborn-5-en-2-01(8) to HS03F under kinetic control. These mixtures differed from the mixture of 9+ 10 observed at higher temperature (-80" to -60") (thermodynamic control). Addition of 3-nortricyclanol(23) or exo-2,3-epoxynorbornane (24) to HS03F at -120"k 10" yielded a mixture containing the exo-2-(fluorosulfonyloxy)-anti-7-and syn-7-norbornylhydroxonium ions (26+ 27) as major adducts. Qualitative rates of the isomerization of 26 + 27 to the more stable ions 9 + 10 and of the isomerization 9 % 10 were evaluated. The solvolysis of 9 + 10 in HS03F yielded the exo-2, exo-5-and exo-2, endo-5-norbornanediyl bis (fluorosulfates) (21 + 22). Norbornadiene and quadricyclane added 2 equivalents of HS03F and furnished kinetically a mixture of exo-2, anti-7-and exo-2, syn-7-norbornanediyl bis (fluorosulfates) (36 + 37) as major adducts. The latter 36+37 were isomerized into a kinetic mixture of the more stable isomers 21 + 22. The rates of these isomerizations were compared. The use of DS03F and (exo-2-D)-norborn-5-en-2-01 (15) confirmed that heterolyses of the fluorosulfates were responsible for the observed isomerization; elimination-addition processes occurred but much more slowly. The results are interpreted in terms of substituted classical and o-bridged secondary 2-norbornyl cation intermediates. It appears that the electron withdrawing substituents FSO, and H20+ (HO) destabilize the o-bridged 2-norbornyl cation more at C(5) than C(7). If the o-bridged ions 5-Z substituted at C(5) by Z=FSO, or H20+ (HO) are transition states in the isomerization of the corresponding classical ions 3-Z,4-Z, the free enthalpy difference between the 'non-classical' o-bridged ion and the classical ions is not higher than the energy barrier to the quenching of the latter intermediates by FSOj in HSO,F/SO*ClF. I) 2,Present address: Lonta AG, CH-3930 Visp, Switzerland. Author, to whom correspondence should be addressed. 336HELVETICA CHIMICA ACTA -Vol. 62, Fasc. 1 (1979) -Nr. 36 Introduction. -The nature of the secondary 2-norbornyl cation has stirred a controversy that is not yet settled [l]. A long-standing problem is whether this carbocation exists as a pair of 'rapidly equilibrating' enantiomorphic structures 1 1' (double minimum energy hypersurface) or as a 'non-classical' o-bridged carbonium ion 2 with C,-symmetry in its ground state (single minimum energy hyper~urface)~).

ChemInform Abstract: 1,2‐SHIFT OF A CARBOXYL GROUP IN A WAGNER‐MEERWEIN REARRANGEMENT

“…At slightly higher temperatures (-90" to -50") the spectra change, particularly the signals of H-C (3) (A6 = + 0.7 ppm) and C (3) (A6 = + 10 ppm), whereas C (1) is only slightly affected ( A 6 = -2 ppm). This change, analogous to that observed with lb, c [20], fits with the well-known replacement of -OH2 by -OSO,F [24] [25] forming 4a. On further heating (-50" to 0') additional signals appear, particularly for H-C(3) (6=5.73) and C(3) (6 = 97.0); the position of these signals and their large coupling constants (44.6 and 180 Hz), very similar to those obtained from lb,c [20], point to the formation of a C,F-bond.…”

Regioselectivity of the Diels‐Alder Additions of 2‐Substituted 5,6 Dimethylidenenorbornanes and‐bicyclo[2.2.2]octanes

“…The regioselectivities 'parayineta' ('p'/'m') are reported in Table 1 The regioisomers p-1 l/m-1 1 -p-15/m-15 were recognized by comparing the 13C-NMR. chemical shifts of the olefinic C-atoms C(2) and C(7) with those calculated for 9-and 10-substituted methyl tricyclo[6.2.1 .02~7]undeca-2(7),4-diene-4-carbox- ylates, assuming y-and 6-substituent effects similar to those reported for 2-substituted 5-norbornenes [7]. The model compound 16 was obtained by addition of methyl propynoate to the diene 1 (see Table 2).…”

Selective Hydrogen Chloride Elimination from Primary Chlorides Induced by the Fluoride Anion. Anchimeric participation of the chloromethyl group in the heterolytic opening of an epoxide. Stereospecific syntheses of 5,6‐bis (methylidene)‐syn‐2‐norbornen‐7‐ol and 5,6‐bis (methylidene)‐endo‐3‐chloro‐exo‐2‐norbornanol

“…; yield: 0.085 g (86%), b.p. [35][36][37][38][39][40] (11). Small portions of Cr03 (1.8 g, 0.018 mol) were added under N2 to a solution at 0" of anh.…”

“…- (4; 48.6 (4; 48.3 (4; 47.0 (d); 46.5 (t, 'JcH= 150 Hz); 34.5 (f, 'JcH= 152 Hz); 34.0 (t, 'JcH= 136 Hz), see Figure. -MS.: 292 (l), 290 (4.5), 288 (Mt,9), 286 (6), 274 (0.5), 272 (3), 270 (Mt -H20, 6). 268 (4), 255 (9), 254 (12), 253 (Mf-C1, 39), 252 ( M t -HCI, 50), 251 (30), 250 (36), 241 (13), 239 (M+-CH2CI, 54), 237 ( a ) , 211 (12), 209 (60), 207 (Mt-Br, loo), 193 (lo), 191 (58), 189 (M+-Br-H20, 93), 173 (33), 171 (Mt -BrCI, 78). C9H13BrC120 (288.02) Calc.…”