A. Annunziata, C. Galli, M. Marinelli, T. Pau
FULL PAPER
2 H, CH2ϭ), 4.3 (s, 2 H, ArCH2), 1.4 (s, 6 H, Me). Ϫ 13C NMR
(CDCl3): δ ϭ 143 (CHϭ), 141Ϫ128 (aromatic carbon atoms), 114
General Procedure of Calibration of a Radical Clock: Precursor 1
(0.9 mmol) was irradiated at 350 nm in benzene (1.8 mL) in the
(CH2ϭ), 97 (CAiprsoϪI), 77.5 (CtertϪO), 76 (ArCH2O), 26 (Me). Ϫ presence of Bu3SnH (0.8 mmol) and azobis(isobutyronitrile)
MS; m/z: 302 [Mϩ], 287 [Mϩ Ϫ Me], 217 [Mϩ Ϫ OCMe2CHϭ (AIBN; 0.09 mmol) for 60 min.[13] The reaction flask was kept at
CH2]. Ϫ C12H15IO (302.15): calcd. C 47.68, H 4.97; found C 47.99,
H 4.78.
25 °C by means of its glass jacket connected to an external thermo-
stat. At the end, an internal standard was added (biphenyl), and
direct analysis of the sample (no workup) by GC and GC-MS gave
the molar amount of the open-chain reduction product 1H, along
with that of the cyclised reduction product 2H. By using the rela-
tionship kC/kH ϭ ([2H] ϫ [Bu3SnH])/[1H], we were able to calculate
the value of kC, since the amount of tin hydride present and the
value of kH are known. In the case of precursor 3 (and 6), the rapid
ring closure of the intermediate open-chain radical to the ring-
closed radical prevented the formation of any open-chain reduced
product 3H (and 6H), even when run with a larger amount of
Bu3SnH. A more efficient H-atom donor was sought and found in
PhSH, whose kH rate constant in the reaction with the phenyl rad-
ical is 1.9ϫ109 Ϫ1 sϪ1 at 25 °C.[21] Therefore, the calibration of
clocks 3 and 6 (0.23 mmol each) was conducted as for 1, but em-
ploying PhSH (0.70 mmol) and AIBN (0.03 mmol) in Me2SO
(1.75 mL) and Bu3SnH (0.26 mL). The values of kC could thus be
calculated.
Synthesis of Products: Anthracene (11H), and naphthalene (12H)
were commercial samples. Analytical samples of 1H, 3H, and 6H
were prepared by alkylation of phenoxide ion with either 4-bromo-
1-butene, allyl bromide or cinammyl bromide, respectively; product
8H was obtained from the alkylation of benzyl bromide with so-
dium 2-methyl-3-butenyl-2-oxide (see above). All these products
were purified by flash chromatography, characterised by MS, and
used for the determination of the GC response factor. In the case
of 9H, the response factor of isomeric 8H was employed. Products
1Ya, 1Yb, 2Ya, 2Yb were obtained from SRN1 photochemical ex-
periments (vide infra), run on a larger scale in a normal flask with-
out temperature control during irradiation, and purified by chro-
matography. Their NMR features were consistent with those al-
ready reported.[7] During chromatography of the residues of these
reactions, product 2H was also obtained in small amounts, as a
1
forerun fraction. Ϫ 2H (oil): H NMR (CDCl3): δ ϭ 7.0Ϫ6.7 (m,
4 H, ArH), 4.00Ϫ3.95 (br. t, 2 H, OCH2), 2.99Ϫ2.92 (m, 1 H,
ArCH), 1.69Ϫ1.63 (m, 2 H, CH2), 1.20Ϫ1.15 (dt, 3 H, CH3). Ϫ
13C NMR (CDCl3): δ ϭ 156 (CiAprsoϪO), 131Ϫ128 (aromatic carbon
atoms), 117 (CAiprsoϪCH), 69 (OCH2), 32 (CH2), 30 (ArCH), 18
(CH3). Ϫ Analytical samples of 4H and 7H were obtained from
the hydrodeiodination of 3 or 6 with Bu3SnH in boiling benzene.
Ϫ 4H (oil): 1H NMR (CDCl3): δ ϭ 7.0Ϫ6.8 (m, 4 H, ArH),
4.50Ϫ4.35 (d, 2 H, OCH2), 3.30Ϫ3.15 (m, 1 H, ArCH), 1.18Ϫ1.15
(d, 3 H, CH3). Ϫ 13C NMR (CDCl3): δ ϭ 154 (CAiprsoϪO), 130Ϫ128
(aromatic carbon atoms), 118 (CAiprsoϪCH), 73 (OCH2), 31 (ArCH),
16 (CH3). Ϫ 7H (oil): 1H NMR (CDCl3): δ ϭ 7.3Ϫ6.8 (m, 9 H,
ArH), 4.45Ϫ4.30 (dt, 2 H, OCH2), 3.75Ϫ3.60 (m, 1 H, ArCH),
3.10Ϫ2.85 (m, 2 H, PhCH2). Ϫ 13C NMR (CDCl3): δ ϭ 158
(CAiprsoϪO), 131Ϫ126 (aromatic carbon atoms), 140 (CiPphsoϪCH2),
120 (CAiprsoϪCH), 75 (CH2), 40 (ArCH), 37 (PhCH2). Ϫ Products
General Procedure for Photostimulated SRN1 Reaction: Under a
stream of argon, the radical clock precursor (0.2 mmol) was added
to a solution of the precursor of the anion (0.7 mmol) and tBuOK
(0.8 mmol) in Me2SO (5 mL). The mixture was stirred at 25 °C
under argon while irradiated with 16 ‘‘350-nm’’ lamps. After an
appropriate time, typically 20Ϫ60 min, the irradiation was stopped,
brine and crushed ice were added, together with a suitable amount
of an internal standard (biphenyl), and the mixture was worked up
with diethyl ether. Concentration to a small volume, and analyses
by GC and GC-MS, allowed for the measurement of the molar
amount of the products formed and for the calculation of kY ac-
cording to the relationship kY/kC ϭ [1Y]/([2H] ϩ [2Y])[YϪ]. The
photostimulated reactions of 11 or 12 (0.2 mmol) with Me3C-
COCH3 (0.29 mmol) and tBuOK (0.33 mmol) in Me2SO (4 mL)
were run analogously for ca. 20 min. Analyses as above gave the
molar amounts of the substitution and reduction products, from
which kY could be reckoned according to the relationship: [ArY]/
[ArH] ϭ kY [YϪ]/kH[SH], using 14.1 for the concentration of
neat Me2SO.
11Y and 12Y were available from a previous investigation.[12b]
Ϫ
Product 7Yc was obtained from the photostimulated reaction
(350 nm) of 6 (0.13 g, 0.6 mmol) with Me3CCOCH3 (240 µL,
1.9 mmol) and tBuOK (0.23 g, 2.0 mmol) in Me2SO (8 mL) for 2 h.
Workup with brine and diethyl ether, followed by chromatography
with hexane/CHCl3 (9:1) on silica gel, gave 7Yc as an oil (70 mg,
Base-Catalysed Isomerisation of 3H: This reaction was conducted
at room temperature in Me2SO with an equimolar amount of
Me3CCOCH2Ϫ Kϩ. Workup with diethyl ether and evaporation of
the solvent left a residue that was carefully distilled in order to
remove Me3CCOCH3 (bp. 100 °C). The residue consisted mainly
of iso-3H, contaminated with ca. 20% of 3H. Similar isomerisations
of allyl ethers to 1-propenyl ethers have been reported.[22] Ϫ 3Η:
1H NMR (CDCl3): δ ϭ 7.3Ϫ6.9 (m, 5 H, ArH), 6.2Ϫ6.0 (m, 1 H,
1
38%). Ϫ H NMR (CDCl3): δ ϭ 7.6Ϫ6.7 (m, 9 H, ArH), 4.65 (dt,
2 H, ArOCH2), 3.75 (dq, 1 H, ArCH), 3.45 (dq, 1 H, CH2CHPh),
3.0Ϫ2.7 (m, 2 H, CH2CO), 1.1 (s, 9 H, CMe3). Ϫ 13C NMR
(CDCl3): δ ϭ 212 (CϭO), 138Ϫ115 (aromatic carbon atoms), 74
(ArOCH2), 43 (CMe3), 41 (CH2CO) 38 (ArCH), 34 (CH2CHPh),
23 (CMe3). Ϫ Compound iso-3Yc was obtained from the photosti-
mulated reaction (350 nm) of 3 (0.37 g, 1.4 mmol) with Me3C-
COCH3 (0.8 mL, 6.4 mmol) and tBuOK (0.73 g, 6.5 mmol) in
Me2SO (20 mL) for 2 h. After workup with diethyl ether, column
chromatography of the residue with hexane/CHCl3 (9:1) on silica
gel gave an oil (0.23 g, 71%), whose NMR spectra are consistent
CHϭ), 5.50Ϫ5.25 (br. q, 2 H, CH2ϭ), 4.55 (dd, 2 H, OCH2). Ϫ
Ar
13C NMR (CDCl3): δ ϭ 158 (C
ϪO), 130 (CH2ϭ), 116
ipso
(CHϭ), 69 (OCH2). Ϫ iso-3H: 1H NMR (CDCl3): δ ϭ 7.3Ϫ6.8 (m,
5 H, ArH), 6.35 (dd, 1 H, OCHϭ), 4.8 (m, 1 H, ϭCHMe), 1.7 (dd,
1
with the structure of iso-3Yc. Ϫ H NMR (CDCl3): δ ϭ 7.3Ϫ6.8
Ar
3 H, Me). Ϫ 13C NMR (CDCl3): δ ϭ 158 (C
(OCHϭ), 107 (ϭCHMe), 26 (Me).
ϪO), 141
ipso
(m, 4 H, ArH), 6.3 (dd, 1 H, OCHϭ), 4.8 (quint, 1 H, MeCHϭ),
3.8 (s, 2 H, ArCH2CO), 1.6 (dd, 3 H, CH3CHϭ), 1.2 (s, 9 H,
CMe3). Ϫ 13C NMR (CDCl3): δ ϭ 213 (CϭO), 142 (OCHϭ), 115
(MeCHϭ), 45 (CMe3), 36 (ArCH2CO), 27 (CMe3), 9 (CH3CHϭ).
Ϫ A DEPT experiment confirmed the presence of only one methyl-
Acknowledgments
ene group: δ ϭ 36 (ArCH2CO). Ϫ MS; m/z: 232 [Mϩ], 191 [Mϩ
Ϫ
CHϭCHMe], 175 [Mϩ Ϫ OCHϭCHMe], 147 [Mϩ Ϫ COCMe3],
Financial support from Italian MURST is gratefully acknow-
ledged.
85 [COCMe3], 57 [CMe3].
1328
Eur. J. Org. Chem. 2001, 1323Ϫ1329