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Helvetica Chimica Acta ± Vol. 82 (1999)
NH3. Elemental analyses were performed in analytical laboratories of the Organic Chemistry Institute of the
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University of Zurich and the Polish Academy of Sciences (CBMiM) in èodz.
2. Starting Materials. The 2,2,4,4-tetramethylcyclobutane-1,3-dione (2) was prepared from 2-methylpropa-
noyl chloride and Et3N in CH2Cl2 by a modified procedure based on the protocol of Miller and Johnson [18]. The
sterically congested 2,2,5,5-tetramethylcyclopentanone and 2,2,6,6-tetramethylcyclohexanone were obtained by
exhaustive methylation of the corresponding cycloalkanones according to [19]. Benzyl(triethyl)ammonium
chloride (TEBA) was prepared from Et3N and PhCH2Cl as recommended by MaÎkosza [20], and
trichloromethyl(phenyl)mercury was synthesized according to [21]. CHCl3 was purified (removal of EtOH)
by treatment with conc. H2SO4 and H2O [22].
3. Reaction of 2 with NaOH/CHCl3 /TEBA. To a soln. of 2 (1.40 g, 10 mmol) and TEBA (200 mg,
0.88 mmol) in CHCl3 (10 ml) in a round bottom flask, 10 ml of a 50% aq. soln. of NaOH were added. The two-
phase system was vigorously stirred, while the temp. was kept at 208 (water bath). The progress of the reaction
5
was followed by recording 1H-NMR spectra of the organic phase ). After ca. 2 h, 2 (s at 1.25 ppm) was
consumed completely. The mixture was diluted with H2O (100 ml) and extracted with CH2Cl2 (3 Â 30 ml), the
combined org. phases were dried (CaCl2), filtered, and evaporated. The aq. phase was acidified with conc.
H2SO4 and saturated with NaCl. The oily layer was extracted with CH2Cl2 (3 Â 30 ml). After usual workup and
6
evaporation, the oily residue obtained was treated with a soln. of CH2N2 in Et2O ).
The mixtures of products from the org. and aq. phases were separated chromatographically (SiO2; hexane
with increasing amounts of CH2Cl2). Three products, 7 ± 9, were obtained from the org. phase and two esters, 12
and 13, from the aq. phase.
4,4-Dichloro-2,2,5,5-tetramethylcyclopentane-1,3-dione (7). Isolated as the first fraction after chromatog-
raphy of the org. phase (hexane/CH2Cl2 6:4). Yield: 223 mg (10%). Colorless crystals. M.p. 34 ± 358 (pentane).
IR (neat): 2950s, 1830m, 1790vs, 1760vs, 1720s, 1660m, 1560m, 1460s, 1370m, 1230s (br.), 1120m, 1100m, 1000m,
930m, 880m, 820w. 1H-NMR: 1.43, 1.37 (2s, 4 Me). 13C-NMR: 213.4, 201.9 (2s, 2 CO); 92.6 (s, CCl2); 59.0, 48.7
.
(2s, C(2), C(5)); 25.3, 21.1 (2q, 4 Me). EI-MS (70 eV): 223 (1, M ), 205(14), 203(43), 175(36), 170(14),
133(24), 99(13), 96(12), 81(81), 72(29), 70(99), 39(100). Anal. calc. for C9H12Cl2O2 (223.10): C 48.45, H 5.42,
Cl 31.78; found: C 48.69, H 5.28, Cl 31.59.
4-(Dichloromethylidene)-2,2,5,5-tetramethylcyclopentane-1,3-dione (9). Isolated as the second fraction
after chromatography of the org. phase (hexane/CH2Cl2 45/55). Yield: 94 mg (4%). Pale-yellow crystals. M.p.
82 ± 838 (MeOH). IR (KBr): 2950m, 1755m (CO), 1705vs (CO), 1555s (CC), 1450m, 1270m, 1100s,
1000w, 895m, 850w, 700w. 1H-NMR: 1.56, 1.23 (2s, 4 Me). 13C-NMR: 218.3, 200.7 (2s, 2 CO); 138.1, 133.3 (2s,
CCCl2); 52.9, 52.2 (2s, C(2), C(5)); 22.8, 21.9 (2q, 4 Me). CI-MS: 252 (100, [M 17] ). EI-MS: 239 (< 1),
.
237(0.7), 235 (1, M ), 199(100), 166(21), 164(33), 138(53), 136(91), 85(15), 70(36). Anal. calc. for
C10H12Cl2O2 (235.11): C 51.08, H 5.14, Cl 30.16; found: C 51.14, H 5.21, Cl 29.78.
2-Chloro-3,3,5,5-tetramethyl-4-oxocyclopent-1-enyl 2,2,4-Trimethyl-3-oxopentanoate (8). Isolated as the
most-polar fraction after chromatography of the org. phase (hexane/CH2Cl2 15/85). Yield: 164 mg (10%).
Colorless crystals. M.p. 73 ± 748 (MeOH). IR (KBr): 2970s, 1760vs (CO), 1700s (CO), 1680m (CC),
1
1460vs, 1270m, 1240s, 1140vs (C O), 1105s, 1050w, 1010s, 900w. H-NMR: 3.07 (sept., J 4.5, Me2CH); 1.53,
1.25, 1.17 (3s, 6 Me); 1.16 (d, J 4.5, Me2CH). 13C-NMR: 216.6 (s, C(4')O); 211.9 (s, C(3)O); 170.0 (s,
C(1)O); 146.1, 128.8 (2s, CC); 56.5, 52.2, 50.7 (3s, C(2), C(1'), C(2')); 37.0 (d, C(4)); 22.9, 22.4, 22.2, 20.5
.
(4q, 8 Me). EI-MS (15 eV): 330 (< 1), 328 (< 1, M ), 141(43), 71(100), 70(2). CI-MS: 346 (100, [M
NH4] ). Anal. calc. for C17H25ClO4 (328.84): C 62.09, H 7.66, Cl 10.78; found: C 62.07, H 7.65, Cl 10.83.
Methyl 2,2,4-Trimethyl-3-oxopentanoate (12). Isolated by distillation of the methyl-ester mixture after
workup of the aq. phase and purified by redistillation at 14 Torr. Yield: 277 mg (16%). Colorless liquid. B.p. 79 ±
808/14 Torr ([23]: b.p. 74.5 ± 758/10 Torr). 1H-NMR: 3.72 (s, MeO); 2.83 (sept., J 6.5, Me2CH); 1.35 (s, 2 Me);
1.07 (d, J 6.5, Me2CH). 13C-NMR: 212.4 (s, CO, ketone); 174.1 (s, CO, ester); 56.0 (s, C(2)); 52.3 (q,
MeO); 36.7 (d, C(4)); 21.8, 20.3 (2q, 4 Me).
Dimethyl 2-Hydroxy-2-isopropyl-3,3-dimethylbutane-1,4-dioate (13). Isolated after chromatography of the
methylated products of the aq. phase as the more-polar fraction and purified by distillation at 0.15 Torr. Yield:
367 mg (16%). Colorless thick liquid. B.p. 62 ± 648/0.15 Torr. IR (neat): 3400m (br., OH), 2950s, 1730vs (CO),
5
)
Ca. 0.5 ml of the CHCl3 soln. was diluted with CH2Cl2, dried (CaCl2), the solvents evaporated, and the
1H-NMR spectrum measured in CDCl3.
The 1H-NMR analysis of the reaction mixture after 2 h displayed a 1:1 ratio of the esters 12 and 13,
whereas, after 3 h, the ratio was determined as 1:3 (s corresponding to MeO at 3.72 and 3.78 ppm, resp.).
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)