F. Ciminale, L. Lopez, A. Nacci, L. D’Accolti, F. Vitale
FULL PAPER
27.55, 26.36 ppm. IR (KBr): ν = 3058, 1709, 701 cm–1. MS (m/z
˜
duced by antimony pentachloride and by aminium salt A,
(b) the observed inhibition of reactions modified by ad-
dition of equimolar amounts (vs. the catalysts) of the non-
nucleophilic base DBP, (c) the characterization of the 1:1
DBP/SbCl5 complex, and (d) the reactivity of aliphatic vic-
diols,[21] which, contrary to aromatic vic-diols,[10a,10c] show
high oxidation potentials not affected by aryl–aryl interac-
tions, to make their preliminary electron-transfer oxidation
totally unsuitable.
%): 224 [M+, 3], 181 (100), 165 (29), 103 (34), 77 (22), 43 (17).
Spiro[adamantane-2,4Ј-homoadamantan-5Ј-one] (2e): M.p. 177 °C
(lit.[18a,23,24] 176–178 °C). 1H NMR (CDCl3): δ = 2.75–2.65 (m, 1
H), 2.55–2.45 (m, 1 H), 2.15–0.77 (m, 26 H) ppm. 13C NMR
(CDCl3): δ = 219.3, 129.8, 127. 8, 49.8, 38.5, 37.7, 36.1, 34.2, 33.4,
32.7, 31.1, 30.6, 29.9, 28.9, 27.9, 27.3, 26.3, 26.2, 25.9, 21.7 ppm.
IR (KBr): ν = 2955, 2931, 2926, 2915, 1681 cm–1. MS (m/z %): 284
˜
(100) [M+].
2,6-Di-tert-butylpyridine/Antimony Pentachloride Complex: On ad-
dition, with stirring at room temperature, of equimolar amounts of
2,6-di-tert-butylpyridine to a dichloromethane solution of anti-
mony pentachloride a dusty, white precipitate was observed. This,
collected by filtration and dried under vacuum, showed the follow-
ing physical and chemical properties: m.p. 128–130 °C. 1H NMR
(500 MHz, CD3CN): δ = 8.48 (t, 1 H), 7.92 (d, 2 H), 1.5 (s, 18
H) ppm. 13C NMR (CD3CN): δ = 164.1, 148.7, 123.6, 37.5,
Experimental Section
Melting points were taken on an electrothermal apparatus and are
uncorrected. 1H and 13C NMR spectra were recorded on Varian
XL 200 and Bruker AM 500 MHz instruments. IR and MS spectra
were performed on a Perkin–Elmer FT-1710 (KBr pellets) and on a
Shimadzu QP5000 instrument, respectively. Optical rotations were
measured with a Perkin–Elmer 241 MC polarimeter. GC analyses
were carried out on a HP 5890A gas chromatograph with a capil-
lary column (ZB-1, 30 m, 0.25 mm i. d.). Dichloromethane was
purified by washing with sulfuric acid solution and distillation over
calcium hydride and was then stored in the dark under nitrogen
and over molecular sieves. Acetonitrile (HPLC grade from Carlo
Erba Co.) was used as received. Starting materials 1a–d, 1f and 2,6-
di-tert-butylpyridine (DBP) were commercial samples from Ald-
rich Co. Aminium salts A1 and B2 and substrate 1e[9] were synthe-
sized by the procedures reported in the literature.
28.8 ppm. IR (KBr): ν = 3374, 3014, 2877, 2861, 2747, 1620, 1529,
˜
1376, 1250, 1190, 888, 819, 738 cm–1. C13H21Cl5NSb (486.92):
calcd. C 31.84, H 4.32, N 2.86; found C 31.35, H 4.10, N 2.78.
[(S)-2,2,3-Trimethyl-3-cyclopentenyl]acetaldehyde (1S,2S,3R,5S)-Pi-
nane Acetal (4f) and [(S)-2,2,4-Trimethyl-3-cyclopentenyl]acetal-
dehyde (1S,2S,3R,5S)-Pinane Acetal (5f): Equimolar amounts of
these acetals were obtained upon treatment of dichloromethane
solutions of 1f with catalytic amounts of antimony pentachloride.
By GC/MS spectrometry, this unsolved pair of reaction products
showed the same fragmentation patterns as authentic samples pre-
pared individually by acid-catalysed (p-toluenesulfonic acid) reac-
tions of pinane diol 1f (85 mg, 0.5 mmol) with equimolar amounts
of (2,2,3-trimethyl-3-cyclopentenyl)acetaldehyde (2f) and (2,2,4-tri-
methyl-3-cyclopentenyl)acetaldehyde (3f) (76 mg, 0.5 mmol),
respectively.[11c] The involvement of the aldehydes 2f and 3f as inter-
mediates in the reactions of diol 1f with catalysts A, B and SbCl5
was accounted for by carrying out similar reactions on DCM solu-
tions of 1f in the presence of an equimolar amount of pinacol 1d.
This reaction led to the simultaneous formation of two different
acetals, namely 4f and 5f, together with (2,2,3-trimethyl-3-cyclopen-
tenyl)acetaldehyde pinacol acetal (7f) and (2,2,4-trimethyl-3-cyclo-
pentenyl)acetaldehyde pinacol acetal (8f). The structure of 7f was
confirmed by an acid-catalysed reaction between the aldehyde 2f
and an excess of 1d, with subsequent comparison of its fragmenta-
tion pattern with that observed in the reaction of the diol 1f carried
out in the presence of pinacol 1d.
Pinacol–Pinacolone Rearrangement of Diols 1a–f by Antimony
Pentachloride. General Procedure: Catalytic amounts of DCM solu-
tions of antimony pentachloride (10 mol %) were rapidly added,
under air at room temperature, to stirred solutions of 1a–f
(100 mol %) in dry CH2Cl2 (10 mL). The solutions adopted a pale
yellow colour, which persisted through the process. The progress of
the reactions was monitored by TLC until completion, and then
by GC and GC/MS spectroscopy. The reaction mixtures were
quenched with sodium hydrogencarbonate solution (NaHCO3
10%, 5 mL), then dichloromethane (10 mL) was added. The or-
ganic layer was separated and dried over sodium sulfate (Na2SO4).
The solvent was removed in vacuo, and the reaction products, iso-
lated by column chromatography (silica gel, petroleum ether/ethyl
ether 10:1 as eluent), were fully characterized by physical, spectro-
scopic data, and comparison with authentic synthesized samples,
already reported in the literature.
Triphenylacetophenone (2a): M.p. 179–180 °C (lit.[4c] 179–180 °C).
Acknowledgments
IR (KBr): ν = 3087, 1674, 701 cm–1. MS (m/z %): 243 (M+ – PhCO,
˜
100), 165 (54), 105 (9), 77 (6).
The authors thank the Ministero dell’Università e della Ricerca
Scientifica e Tecnologica (MIUR).
Triphenylacetaldehyde (2b): M.p. 104–105 °C (lit.[13b] 104–105 °C).
1H NMR (CDCl3): δ = 10.28 (s, 1 H) 7.25–7.06 (m, 15 H) ppm. IR
(KBr): ν = 3058, 2724, 1685 cm–1. MS (m/z %): 243 (M+ – CHO,
˜
[1] T. N. Baker, W. P. Doherty, W. S. Kelly, W. Newmeyer, J. E.
Rogers, R. E. Spaulding, R. I. Walters, J. Org. Chem. 1965, 30,
3714–3718.
[2] F. A. Bell, A. Ledwith, D. C. Sherrington, J. Chem. Soc. C
1969, 2719–2720.
[3] a) N. L. Bauld, Tetrahedron 1989, 45, 5307–5363; b) M.
Schmittel, A. Burghart, Angew. Chem. Int. Ed. Engl. 1997, 36,
2550–2589; c) S. F. Nelsen, Acc. Chem. Res. 1987, 20, 269–276.
[4] a) P. G. Gassman, D. A. Singleton, J. Am. Chem. Soc. 1984,
106, 7993–7995; b) F. G. Bordwell, M. J. Bausch, J. Am. Chem.
Soc. 1986, 108, 2473–2474; c) D. Sul Han, H. J. Shine, J. Org.
Chem. 1996, 61, 3977–3982; d) H. Hart, A. Teuerstein, M. A.
Babin, J. Am. Chem. Soc. 1981, 103, 903–906; e) L. Eberson,
100), 165 (56).
Benzhydryl Phenyl Ketone (3b): M.p. 134–135 °C (lit.[13b] 133–
1
135 °C). H NMR (CDCl3): δ = 8.03–7.95 (m, 2 H), 7.58–7.18 (m,
13 H), 6.06 (s, 1 H) ppm. 13C NMR (CDCl3): δ = 199.82, 139.35,
137.05, 133.21, 129.30, 129.11, 128.97, 127.83, 59.43 ppm. IR
(KBr): ν = 3065, 2978, 1683 cm–1. MS (m/z %): 272 [M+, 2], 167
˜
(40), 105 (100), 77 (19).
3,3-Diphenylbutan-2-one (2c): M.p. 41 °C (lit.[10a] 41 °C). H NMR
1
(CDCl3): δ = 7.38–7.21 (m, 10 H), 2.14, (s, 3 H), 1.90 (s, 3 H) ppm.
13C NMR (CDCl3): δ = 209.04, 143.52, 128.30, 126.85, 62.25,
1602
© 2005 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Org. Chem. 2005, 1597–1603