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M. Dejmek et al.
PAPER
action conversion. Column chromatography was performed on
silica gel (40–60 mm). HRMS analysis of pure compounds was con-
ducted on an LTQ Orbitrap XL instrument (Thermo Fisher Scientif-
ic). Melting points are uncorrected. Microwave syntheses were
carried out in a CEM Discover instrument with a single-mode cav-
ity and focused microwave heating (microwave power supply 0–
300 W, 1 W increments, IR temperature sensor, sealed vessel mode,
pressure range 0–20 bar, 10 mL or 80 mL vials). Chemicals and sol-
vents were purchased and used as received. The yields are first re-
ported as those for chromatographically purified compounds and
then for compounds purified by crystallization or distillation (see
below).
Ethyl (1R*,2S*,4S*)-1,4,5,6,7,7-Hexachlorobicyclo[2.2.1]hept-
5-ene-2-carboxylate (5a)18a
Yield: 603 mg (81%); white solid; or yield: 519 (71%); white crys-
tals; mp 70 °C (Lit.18a 69 °C).
1H NMR (500 MHz, CDCl3): d = 1.31 (t, JCH3,CH2 = 7.1 Hz, 3
H,CH3), 2.58 (dd, Jgem = 12.5, J3en,2 = 4.1 Hz, 1 H, H-3endo), 2.68
(dd, Jgem = 12.5, J3ex,2 = 8.9 Hz, 1 H, H-3exo), 3.61 (dd, J2,3ex = 8.9,
J2,3en = 4.1 Hz, 1 H, H-2), 4.14–4.27 (m, 2 H, CH2).
13C NMR (126 MHz, CDCl3): d = 14.06 (CH3), 38.10 (C-3), 50.49
(C-2), 62.26 (CH2), 78.44 and 80.84 (C-1, C-4), 102.53 (C-7),
129.53 (C-6), 132.32 (C-5), 168.41 (COO).
HRMS (ESI): m/z calcd for C10H8O2Cl6: 369.8655; found:
369.8664.
Small-Scale Diels–Alder Reaction in Microwave Synthesizer;
General Procedure
A 1:2 molar mixture of dicyclopentadiene (1; 1.5 mmol) and the
corresponding dienophile (3 mmol) with hydroquinone (10 mg), or
an equimolar mixture of chlorinated diene 3 or 4 (2 mmol) and the
corresponding dienophile (2 mmol), was heated in a sealed micro-
wave vessel at the specified temperature for a given period of time
(Tables 1 and 2). The crude reaction mixture (sufficient conversion
of diene determined by GC-MS) was chromatographed (silica gel,
25 g; EtOAc–hexane, 1:99 to 3:97). Chlorinated compounds with a
suitable melting point may also be crystallized (MeOH with a few
drops H2O). To achieve sufficient purity of the acquired crystals in
the cases of 5h and 5i, filtration through a plug of silica was neces-
sary. The purity of all prepared compounds was confirmed by GC-
MS analysis (>98%).
(1R*,2R*,4S*)-1,4,5,6,7,7-Hexachlorobicyclo[2.2.1]hept-5-en-2-
yl Acetate (5b)18b
Yield: 580 mg (81%); colorless solid; mp 44 °C (Lit.18b 44 °C).
1H NMR (500 MHz, CDCl3): d = 2.01 (dd, Jgem = 13.3, J3en,2 = 2.5
Hz, 1 H, H-3endo), 2.11 (s, 3 H, CH3), 3.05 (dd, Jgem = 13.3,
J3ex,2 = 7.7 Hz, 1 H, H-3exo), 5.70 (dd, J2,3ex = 7.7, J2,3en = 2.5 Hz, 1
H, H-2).
13C NMR (126 MHz, CDCl3): d = 20.51 (CH3), 43.42 (C-3), 77.03
(C-2), 78.21 and 81.27 (C-1, C-4), 100.78 (C-7), 130.22 (C-6),
132.58 (C-5), 169.63 (COO).
HRMS (ESI): m/z calcd for C9H6O2Cl6: 355.8499; found: 355.8500.
Ethyl (1R*,2R*,4S*)-1,4,5,6,7,7-Hexachlorobicyclo[2.2.1]hept-
5-en-2-yl Ether (5c)18c
Yield: 215 mg (31%); brownish oil.
(1R*,4R*,5R*)-5-Phenylbicyclo[2.2.1]hept-2-ene (2e)17c
Yield: 410 mg (80%); colorless liquid [chromatographically insep-
arable mixture of endo/exo-isomers (4:1)].
1H NMR (500 MHz, CDCl3): d = 1.34 (ddd, Jgem = 11.8, J6en,5 = 4.8,
J5en,7a = 2.5 Hz, 1 H, H-6endo), 1.49 (dm, Jgem = 8.1 Hz, 1 H, H-7b),
1.53 (dm, Jgem = 8.1 Hz, 1 H, H-7a), 2.22 (ddd, Jgem = 11.8,
J6ex,5 = 9.3, J6ex,1 = 3.8 Hz, 1 H, H-6exo), 2.98 (m, 1 H, H-1), 3.11
(m, 1 H, H-4), 3.41 (m, 1 H, H-5), 5.82 (ddm, J3,2 = 5.7, J3,4 = 2.9
Hz, 1 H, H-3), 6.28 (ddm, J2,3 = 5.7, J2,1 = 3.1 Hz, 1 H, H-2), 7.15–
7.33 (m, 5 H, H-2¢, H-3¢, H-4¢).
1H NMR (500 MHz, CDCl3): d = 1.18 (t, JCH3,CH2 = 7.0 Hz, 3 H,
CH3), 1.98 (dd, Jgem = 12.8, J3en,2 = 2.3 Hz, 1 H, H-3endo), 2.87 (dd,
Jgem = 12.8, J3ex,2 = 7.5 Hz, 1 H, H-3exo), 3.62 and 3.85 (dq,
Jgem = 9.3, JCH2,CH3 = 7.0 Hz, 2 H, OCH2), 4.47 (dd, J2,3ex = 7.5,
J2,3en = 2.3 Hz, 1 H, H-2).
13C NMR (126 MHz, CDCl3): d = 15.25 (CH3), 43.71 (C-3), 67.38
(OCH2), 78.28 and 82.88 (C-1, C-4), 83.71 (C-2), 101.30 (C-7),
130.34 (C-6), 131.47 (C-5).
13C NMR (126 MHz, CDCl3): d = 32.94 (C-6), 43.19 (C-1), 43.47
(C-5), 48.58 (C-4), 50.22 (C-7), 125.57 (C-4¢), 127.59 (C-3¢),
128.23 (C-2¢), 132.79 (C-3), 137.15 (C-2), 145.02 (C-1¢).
HRMS (ESI): m/z calcd for C9H8OCl6: 341.8706; found: 341.8710.
Diethyl (1R*,2S*,3S*,4S*)-1,4,5,6,7,7-Hexachlorobicyc-
lo[2.2.1]hept-5-ene-2,3-dicarboxylate (5d)17b
Yield: 320 mg (36%); brownish oil.
1H NMR (500 MHz, CDCl3): d = 1.33 and 1.34 (t, JCH3,CH2 = 7.2 Hz,
6 H, CH3), 3.50 (d, J3,2 = 5.4 Hz, 1 H, H-3), 4.24 (d, J2,3 = 5.4 Hz, 1
H, H-2), 4.18–4.34 (m, 4 H, CH2).
HRMS (ESI): m/z calcd for C13H14: 170.1096; found: 170.1091.
(1R*,2R*,4R*)-Bicyclo[2.2.1]hept-5-en-2-yl Benzoate (2g)17e
Yield: 525 mg (82%); colorless liquid [chromatographically separa-
ble mixture of endo/exo-isomers (7:2)]. The endo-isomer has not
been described before.
13C NMR (126 MHz, CDCl3): d = 14.07 (CH3), 51.72 (C-3), 53.24
(C-2), 62.41 and 62.66 (CH2), 79.89 and 79.99 (C-1, C-4), 101.94
(C-7), 131.85 (C-6), 133.75 (C-5), 166.07 and 168.07 (COO).
1H NMR (500 MHz, CDCl3): d = 1.09 (dm, Jgem = 12.6 Hz, 1 H, H-
3endo), 1.42 (dm, Jgem = 8.9 Hz, 1 H, H-7b), 1.54 (dm, Jgem = 8.9
Hz, 1 H, H-7a), 2.26 (ddd, Jgem = 12.6, J3ex,2 = 8.1, J3ex,4 = 3.7 Hz, 1
H, H-3exo), 2.92 (m, 1 H, H-4), 3.27 (m, 1 H, H-1), 5.54 (ddd,
J2,3ex = 8.1, J2,1 = 4.0, J2,3en = 2.6 Hz, 1 H, H-2), 6.08 (ddm,
J6,5 = 5.7, J6,1 = 2.9 Hz, 1 H, H-6), 6.39 (ddm, J5,6 = 5.7, J5,4 = 3.1
Hz, 1 H, H-5), 7.42 (m, 2 H, H-3¢), 7.54 (m, 1 H, H-4¢), 7.97 (m, 2
H, H-2¢).
HRMS (ESI): m/z calcd for C13H12O4Cl6: 441.8867; found:
441.8881.
(1R*,4S*,5R*)-1,2,3,4,7,7-Hexachloro-5-phenylbicyc-
lo[2.2.1]hept-2-ene (5e)18d
13C NMR (126 MHz, CDCl3): d = 34.83 (C-3), 42.30 (C-4), 45.96
(C-1), 47.66 (C-7), 75.62 (C-2), 128.28 (C-3¢), 129.47 (C-2¢),
130.54 (C-1¢), 131.58 (C-6), 132.73 (C-4¢), 138.59 (C-5), 166.71
(COO).
Yield: 720 mg (95%); white solid; or yield: 636 mg (84%); white
crystals; mp 69–70 °C (Lit.18d 73 °C).
1H NMR (500 MHz, CDCl3): d = 2.51 (dd, Jgem = 13.0, J6en,5 = 4.2
Hz, 1 H, H-6endo), 2.93 (dd, Jgem = 13.0, J6ex,5 = 9.2 Hz, 1 H, H-
6exo), 3.99 (dd, J5,6ex = 9.1, J5,6en = 4.2 Hz, 1 H, H-5), 7.11 (m, 2 H,
H-2¢), 7.32–7.36 (m, 3 H, H-3¢, H-4¢).
HRMS (ESI): m/z calcd for C14H14O2: 214.0994; found: 214.0988.
13C NMR (126 MHz, CDCl3): d = 40.73 (C-6), 51.66 (C-5), 78.98
and 84.11 (C-1, C-4), 102.85 (C-7), 128.44 (C-4¢), 128.53 (C-3¢),
128.93 (C-2¢), 131.05 and 131.17 (C-2, C-3), 134.22 (C-1¢).
Synthesis 2011, No. 24, 4077–4083 © Thieme Stuttgart · New York