Alternative synthesis of 2-hydroxy-3,5,5-trimethylcyclopent-2-en-1-one

Article abstract of DOI:10.1002/hlca.200900231

The 2-hydroxy-3,5,5-trimethylcyclopent-2-en-1-one (1) was synthesized in 42% yield by rearrangement of epoxy ketone 10 on treatment with BF₃ ? Et₂O under anhydrous conditions. Intermediate 10 was available from the known enone 8, either via direct epoxidation (60% H₂O ₂ , NaOH, MeOH; yield 50%), or via reduction to the corresponding allylic alcohol 14 (LiAlH₄, THF), followed by epoxidation ([VO(acac)₂], ^tBuOOH) and reoxidation under Swern conditions, in 37% total yield.

Full text of DOI:10.1002/hlca.200900231

Helvetica Chimica Acta – Vol. 93 (2010)
111
Alternative Synthesis of 2-Hydroxy-3,5,5-trimethylcyclopent-2-en-1-one
by Christian Chapuis* and Christine Saint-Le´ger
Firmenich SA, Corporate R&D Division, P.O. Box 239, CH-1211 Geneva 8
(phone: þ 41-22-7803610; fax: þ 41-22-7803334; e-mail: Christian.chapuis@firmenich.com)
The 2-hydroxy-3,5,5-trimethylcyclopent-2-en-1-one (1) was synthesized in 42% yield by rearrange-
ment of epoxy ketone 10 on treatment with BF3 · Et2O under anhydrous conditions. Intermediate 10 was
available from the known enone 8, either via direct epoxidation (60% H2O2, NaOH, MeOH; yield 50%),
or via reduction to the corresponding allylic alcohol 14 (LiAlH4, THF), followed by epoxidation
t
([VO(acac)2], BuOOH) and reoxidation under Swern conditions, in 37% total yield.
Introduction. – The title compound 1 was first isolated from the essential oil of
Backhousia angustifolia in 1931 [1] and later identified in roasted coffee [2], as well as
in the Maillard reaction of casein pancreatic hydrolyzate derived peptides with glucose
[3]. Three syntheses have been published which are summarized in Scheme 11). The
first one consisted in the stoechiometric SeO2 oxidation of 2,4,4-trimethylcyclopenta-
none (2) [5b – 5d] giving 1 in 25% yield [5a].
Intermediate 22) is readily available, either via the corresponding enone 3 [6], by
acidic cyclization of isobutyl methacrylate (¼2-methylpropyl 2-methylprop-2-enoate)
[7], followed by hydrogenation, or from isophorone 4, via sequential BF3 · Et2O
rearrangement and NaOH treatment of its corresponding epoxide [8]. Alternatively,
hydrolytic NaOH treatment of either the tetrachlorocyclohexanone 5b, with air
oxidation, or dichlorocyclopentanone 6b, afforded the desired compound 1 [9]. Finally,
ingredient 1 was also unselectively obtained, as an inseparable mixture of mono- [10],
di- [11], and trimethylated material, by alkylation of cyclotene 7a via its ketimine
derivative [12]. Nevertheless, none of these approaches is eligible for a viable industrial
process for the safe production of a flavor, due to the toxicity of SeO2, Cl2, or trace
amounts of halogenated materials in the last step. We thus decided to explore and
present here an alternative approach, starting from cyclopentenone 8 [13], using
classical scalable conditions.
Results and Discussion. – Alkylation of isobutyric acid 9a with lithium diisopro-
pylamide (LDA) and methallyl chloride (¼ 3-chloro-2-methylprop-1-ene) afforded
practically quantitatively the reported acid 9b (95% yield) [14], which was cyclized
with polyphosphoric acid into cyclopentenone 8, with an improved yield of 83%
[13f][15] (Scheme 2). Hydrogenation of enone 8 was already reported to afford
1
)
)
For the photolysis of 1, see [4].
13C-NMR Data: 221.8 (s); 52.7 (t); 46.1 (t); 42.9 (d); 34.0 (s); 29.8 (q); 28.0 (q); 14.9 (q).
2
ꢀ 2010 Verlag Helvetica Chimica Acta AG, Zꢁrich

112
Helvetica Chimica Acta – Vol. 93 (2010)
Scheme 1
i) SeO2, EtOH, 788. ii) H2, Pd/C, EtOH. iii) 35% H2O2, NaOH, MeOH. iv) BF3 · Et2O, then NaOH. v)
PhNH2, TsOH, then 2 equiv. of NaH, THF, MeI, then 15% HCl. vi) Cl2, CCl4, cat. DMF. vii) 3n NaOH,
1008. viii) HNO3, NH4VO3. ix) Dist./Ba(OH)2.
cyclopentanone 6a3) [16] in 95% yield [13b,c] (Scheme 1). We unsuccessfully
t
attempted the oxidation of 6a with either SeO2/EtOH or the more practical BuOK/
O2 conditions [17]. We then came back to our initial strategy by epoxidizing the C¼C
bond (60% H2O2 solution, NaOH, MeOH), and could isolate the epoxy ketone 104) in
50% yield5) [19]. We also tried acidic mCPBA (3-chloroperbenzoic acid) conditions
but, as expected, obtained the corresponding epoxy lactone 12 in a poor 12% yield6).
To oxidize the a-position of enone 8, we also treated it with two equiv. of BH3 · THF.
Thus, after oxidative NaOH/H2O2 workup, we isolated diol 13 in 61% yield. Further
oxidation (pyridinium chlorochromate (PCC), CH2Cl2) furnished a sample of 1 in 17%
yield. The efficiency of this process could be improved by using Swern conditions
(oxalyl chloride, CH2Cl2, DMSO, Et3N, 25% yield) during the last step7). This
nonindustrial approach at least allowed us to obtain a sample of 1, thus facilitating the
.
MS Data: 126 (38, Mþ ), 111 (27), 83 (50), 69 (48), 56 (100), 41 (48).
3
4
)
)
Both 8 and 10 possess very similar tR on both polar and apolar capillary GC columns, and UV/TLC
or GC/IR analyses are recommended to follow the reaction.
The known unsaturated lactone 11 was isolated as a by-product in 10% yield on using 30% H2O2
solution, beside 10 (30% yield). Phase-transfer conditions (30% H2O2 solution, Me3BnNCl, CH2Cl2,
H2O, NaOH [10a]) were cleaner but also less efficient (35% yield), while (KF-Al2O3, tBuOOH [18])
gave only 15% partial conversion.
5
)
6
7
)
Alternative less industrial conditions, oxone [20] or F2/H2O/MeCN/CH2Cl2 [21], were not
attempted.
)
Dess – Martin conditions gave the worst result (8% of 1), besides numerous linear derivatives of
2,2,4-trimethylpentanedial [22]; data of 2,2,4-trimethylpentanedial: 1H-NMR: 9.57 (d, J ¼ 2, 1 H);
9.45 (s, 1 H); 2.42 – 2.35 (m, 1 H); 2.11 (dd, J ¼ 7, 14, 1 H); 1.44 (dd, J ¼ 5.5, 14, 1 H); 1.11 (d, J ¼ 7,
3 H); 1.09 (s, 3 H); 1.08 (s, 3 H). 13C-NMR: 205.3 (d); 203.8 (d); 45.7 (s); 42.8 (d); 37.2 (t); 22.2 (q);
.
21.7 (q); 15.6 (q). MS: 142 (1, Mþ ), 113 (5), 95 (16), 72 (32), 58 (48), 43 (100), 41 (35). For an
untested alternative aerobic oxidative technique, see [23].

Helvetica Chimica Acta – Vol. 93 (2010)
113
Scheme 2
i) LDA, THF, methallylCl (ClCH2C(Me)¼CH2). ii) H3PO4. iii) 30% H2O2, NaOH, MeOH. iv) mCPBA,
CH2Cl2, 08. v) BH3 · THF, THF. vi) (COCl)2, DMSO, Et3N, ꢀ 108. vii) LiAlH4, THF, 08. viii) tBuOOH,
toluene, [VO(acac)2]. ix) 15% HCl. x) 0.2% H2SO4, 1008. xi) BF3 · Et2O, CH2Cl2. xii) 60% H2O2, NaOH,
MeOH.
analysis of alternative processes. Since enone 8 seemed sensitive to oxidative
conditions, and prone to Bayer– Villiger reaction, we also decided to reduce it
(LiAlH4, THF, 88% yield) to the corresponding allyl alcohol 14. At this stage, we could
readily and stereoselectively epoxidize the C¼C bond (tBuOOH, [VO(acac)2], 62%
yield, [24]) to the cis-epoxy alcohol 158). This compound is also very sensitive and was
readily transformed into triol 16 by a simple washing with 15% aqueous HCl solution
during an extraction. Swern oxidation of 15 (oxalyl chloride, DMSO, Et3N, 67% yield)
afforded the desired epoxy ketone 10. Following a known procedure, used for a
monomethylated isomer [9], we attempted to isomerize 10 with 0.2% H2SO4 solution,
but isolated instead of 1 the crystalline dihydroxy ketone 17 in 15% yield. Formally, a
further dehydration at a more acidic pH should result in the target molecule [25], but
8
)
Due to the geometry of the five-membered ring, and even with the NOESY experiments in hand,
we were unable to fully ascertain the relative cis or trans configuration of both OH groups in
1
structures of 13, 16, and 17, based on undisputable arguments. Simulated H-NMR and IR spectra
suggest the following relative configurations: rel-(1RS,2SR,5SR)-13; rel-(1RS,2RS,3RS)-16; rel-
(4RS,5SR)-17; but in view of the absence of chirality in the final compound 1, further derivatizations
or X-ray structure analyses were not undertaken.

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Helvetica Chimica Acta – Vol. 93 (2010)
we preferred instead to directly isomerize epoxide 10 by treatment with BF3 · Et2O
under anhydrous conditions. Thus, we readily obtained the desired crystalline flavor
ingredient 1 in 42% yield9). Although this alternative approach is longer and globally
less efficient than the direct epoxidation of enone 8, this reduction/oxidation route
could eventually be shortened by a direct access to the allyl alcohol 1410).
Conclusion. – We could obtain pure 1 by rearrangement of epoxy ketone 10 with
BF3 · Et2O under anhydrous conditions (42% yield)9). This latter intermediate is
available from the reported enone 8, either by direct 60% H2O2/NaOH epoxidation
(50% yield)11) or, less efficiently (37% yield), via [VO(acac)2]/tBuOOH epoxidation
of the corresponding allyl alcohol 14, prior to reoxidation under Swern conditions.
Another two-step transformation of 8, involving a hydroboration/Swern oxidation
sequence, is less industrial (15% global yield).
We are indebted to Dr. Jean-Yves de Saint Laumer for calculations of the coupling constants in
theoretical 1H-NMR analyses (CDCl3) of 13 and 16 ).
12
Experimental Part
General. See [26]. All the chiral compounds presented here were obtained as racemates.
2-Hydroxy-3,5,5-trimethylcyclopent-2-en-1-one (1). BF3 · Et2O (1.6 g, 11 mmol) was added dropwise
to a soln. of epoxy ketone 10 (15.5 g, 110 mmol) in CH2Cl2 (200 ml). After 2 h at 208, the mixture was
diluted with CH2Cl2 (100 ml) and washed with sat. aq. NaHCO3 soln. to neutrality. The org. phase was
dried (Na2SO4) and concentrated and the residue bulb-to-bulb distilled: pure 1 (42%). White crystals.
M.p. (pentane) 84.5 – 85.58. B.p. 778/6 mbar. IR: 3501, 3421, 3329, 2968, 2928, 2869, 1756, 1695, 1651, 1460,
1404, 1358, 1299, 1234, 1197, 1177, 1147, 1087, 1055, 1028, 959, 932, 839, 781, 704, 658. 1H-NMR: 2.30 (q,
J ¼ 1.5, 2 H); 2.00 (t, J ¼ 1.5, 3 H); 1.30 (s, 6 H); 1.28 (s, OH). 13C-NMR: 208.3 (s); 146.4 (s); 142.4 (s);
.
44.8 (t); 41.2 (s); 25.1 (2q); 14.2 (q). MS: 140 (100, Mþ ), 125 (85), 107 (22), 97 (26), 85 (15), 79 (18), 69
(23), 56 (20), 43 (22), 41 (27).
3,5,5-Trimethylcyclopent-2-en-1-one (8). A mixture of enone 9b (17.8 g, 125 mmol) and polyphos-
phoric acid (85 g) was heated to 1408 for 4 h. Ice (100 g) was added to the cold mixture which was then
stirred for 1 h. The aq. phase was extracted with Et2O (5 ꢁ 80 ml), the org. phase washed to neutrality
with sat. aq. NaHCO3 soln. and then H2O, dried (Na2SO4), and concentrated, and the residue distilled:
pure 8 (83%). B.p. 678/8.5 to 628/7.4 mbar. IR: 2960, 2926, 2867, 1701, 1624, 1432, 1378, 1323, 1302, 1224,
1
1128, 1099, 848, 720, 616. H-NMR: 5.85 (s, 1 H); 2.44 (s, 2 H); 2.11 (s, 3 H); 1.11 (s, 6 H). 13C-NMR:
.
214.6 (s); 175.5 (s); 128.0 (d); 49.7 (t); 44.6 (s); 25.0 (2q); 19.4 (q). MS: 124 (30, Mþ ), 109 (100), 81 (28),
79 (15), 53 (8), 41 (9), 39 (12).
2,2,4-Trimethylpent-4-enoic Acid (9b). Obtained in 95% yield according to [14] and [13f]. B.p. 808/
8 mbar. IR: 3076, 2972, 2931, 1696, 1474, 1448, 1407, 1366, 1311, 1279, 1221, 1163, 1137, 942, 893, 867, 825,
9
)
Compound 1 is also very sensitive to purification conditions. For example, a column
chromatography (SiO2) with the eluent AcOEt should be avoided due to partial transesterification
.
to the corresponding 2,4,4-trimethyl-5-oxocyclopent-1-en-1-yl acetate. MS: 182 (0, Mþ ), 140 (96),
125 (74), 112 (23), 107 (13), 97 (22), 85 (27), 69 (19), 56 (38), 43 (100), 41 (39).
Thus, for example, the intramolecular oxo – ene reaction of 2,2,4-trimethylpent-4-enal was already
reported to form the endocyclic homoallyl alcohol, an analogue of 14 [13a].
This shorter access will be further optimized.
10
)
11
12
)
)
3
13: J ¼ 4.8 vs. 8.5 Hz between trans-positioned HꢀC(1) and HꢀC(5) for cis- vs. trans-positioned
OHꢀC(1) and OHꢀC(2), resp. 16: 3J ¼ 5.2 vs. 7.6 Hz between trans-positioned OHꢀC(1) and
OHꢀC(2) for cis- vs. trans-positioned OHꢀC(3) and OHꢀC(2), resp.

Helvetica Chimica Acta – Vol. 93 (2010)
115
788. 1H-NMR: 12.0 (s, OH); 4.84 (s, 1 H); 4.71 (s, 1 H); 2.34 (s, 2 H); 1.72 (s, 3 H); 1.21 (s, 6 H).
.
13C-NMR: 185.2 (s); 142.2 (s); 114.5 (t); 48.2 (t); 42.0 (s); 25.4 (2q); 23.6 (q). MS: 142 (10, Mþ ), 127 (16),
97 (100), 81 (14), 70 (15), 55 (52), 41 (23).
3,3,5-Trimethyl-6-oxabicyclo[3.1.0]hexan-2-one (10). DMSO (1.2 g, 15 mmol) was added dropwise
at ꢀ 708 to a soln. of (COCl)2 (981 mg, 7.7 mmol) in CH2Cl2 (14 ml). A soln. of alcohol 15 (1.0 g, 7 mmol)
in CH2Cl2 (7 ml) was added dropwise, followed, after 0.25 h, by Et3N (3.55 g, 35 mmol). The temp. was
then slowly increased to 208 during 1 h, Et2O (30 ml) was added, and the org. phase was washed to
neutrality with aq. sat. NH4Cl soln., dried, and concentrated. Bulb-to-bulb distillation afforded pure
ketone 10 (67%). B.p. 718/0.7 mbar. IR: 2967, 2930, 2869, 1741, 1470, 1450, 1410, 1382, 1360, 1268, 1226,
1144, 1126, 1060, 918, 865, 809, 774, 710, 682, 613. 1H-NMR: 3.24 (s, 1 H); 2.20 (d, J ¼ 14.7, 1 H); 1.84 (d,
J ¼ 14.7, 1 H); 1.56 (s, 3 H); 1.13 (s, 3 H); 1.06 (s, 3 H). 13C-NMR: 214.7 (s); 64.0 (s); 62.2 (d); 43.4 (t); 43.2
.
(s); 27.6 (q); 25.9 (q); 18.2 (q). MS: 140 (95, Mþ ), 125 (9), 109 (18), 97 (65), 83 (75), 70 (100), 55 (68), 43
(72), 41 (80), 39 (45).
4,4,6-Trimethyl-3,7-dioxabicyclo[4.1.0]heptan-2-one (12). A soln. of enone 8 (300 mg, 2.4 mmol) in
CH2Cl2 (5 ml) was added at 08 to a soln. of 70% mCPBA (600 mg, 2.4 mmol) in CH2Cl2 (5 ml). After
18 h at 208, the mixture was diluted with CH2Cl2 and extracted with sat. aq. NaHCO3 soln. The org. phase
was washed to neutrality with H2O, dried (Na2SO4), and concentrated and the residue purified by CC
(SiO2 ; Et2O): pure 12 (12%). B.p. 758/0.15 mbar. IR: 2980, 2934, 1725, 1445, 1419, 1386, 1372, 1362, 1303,
1281, 1198, 1133, 1075, 1018, 997, 984, 908, 855, 834, 808, 761, 735, 686. 1H-NMR: 3.36 (s, 1 H); 2.20 (d, J ¼
15, 1 H); 2.10 (d, J ¼ 15, 1 H); 1.55 (s, 3 H); 1.48 (s, 3 H); 1.39 (s, 3 H). 13C-NMR: 168.6 (s); 81.3 (s); 60.1
.
(s); 53.8 (d); 38.8 (t); 31.7 (q); 29.6 (q); 21.0 (q). MS: 156 (1, Mþ ); 100 (20), 97 (63), 83 (14), 69 (43), 55
(26), 43 (100), 41 (46).
3,3,5-Trimethylcyclopentane-1,2-diol (13). A soln. of BH3 · THF complex (1.0m in THF; 32 ml,
32 mmol) was added dropwise at 08 to a soln. of enone 8 (2.0 g, 16 mmol) in THF (20 ml). After 1.5 h, a
15% aq. NaOH soln. (4 ml) was added, followed at 08 by 35% H2O2 soln. (2.0 ml). The mixture was
diluted with Et2O (30 ml) and washed to neutrality with H2O. The org. phase was dried (Na2SO4) and
concentrated and the residue purified by CC (SiO2 ; cyclohexane/Et2O 95 :5 ! 5 :95): pure 13 (61%).
This material crystallized from cyclohexane. M.p. 74 – 778. IR: 3223, 2969, 2954, 2925, 2892, 2863, 1457,
1346, 1286, 1117, 1068, 1016, 999, 911, 843, 790, 715. 1H-NMR: 3.72 (br. s, 2 OH); 3.46 (d, J ¼ 4.3, 2 H);
1.80 – 1.70 (m, 2 H); 1.20 – 1.10 (m, 1 H); 1.05 (d, J ¼ 7, 3 H); 1.04 (s, 3 H); 0.93 (s, 3 H). 13C-NMR: 85.7
.
(d); 83.8 (d); 44.3 (t); 36.7 (s); 34.4 (d); 29.6 (q); 24.9 (q); 18.7 (q). MS: 144 (8, Mþ ), 126 (16), 111 (69),
88 (28), 83 (54), 71 (100), 69 (76), 57 (70), 43 (56), 41 (70).
3,5,5-Trimethylcyclopent-2-en-1-ol (14). A soln. of enone 8 (6.7 g, 53 mmol) in Et2O (10 ml) was
added dropwise at 08 to a suspension of LiAlH4 (1.0 g, 27 mmol) in Et2O (230 ml). After 2 h at 208, H2O
(1 ml), 15% NaOH soln. (1 ml), and H2O (10 ml) were successively added. The mixture was filtered and
the filtrate dried (MgSO4) and concentrated. Bulb-to-bulb distillation afforded pure 14 (88%). B.p. 688/
9.0 mbar. IR: 3337, 3045, 2953, 2911, 2866, 2839, 1658, 1466, 1440, 1378, 1363, 1322, 1195, 1154, 1038, 1020,
992, 942, 885, 865, 825, 671.1H-NMR: 5.38 (s, 1 H); 4.13 (s, 1 H); 2.22 (d, J ¼ 16.2, 1 H); 1.94 (d, J ¼ 16.2,
1 H); 1.73 (s, 3 H); 1.26 (br. s, OH); 1.05 (s, 3 H); 1.04 (s, 3 H). 13C-NMR: 145.0 (s); 126.4 (d); 85.2 (d);
.
50.4 (t); 42.2 (s); 28.7 (q); 22.8 (q); 17.1 (q). MS: 126 (8, Mþ ), 111 (100), 108 (30), 93 (99), 91 (55), 77
(43), 55 (20), 43 (20), 41 (18), 39 (20).
3,3,5-Trimethyl-6-oxabicyclo[3.1.0]hexan-2-ol (15). At 208, 70% aq. tBuOOH soln. (9.0 g, 70 mmol)
was added dropwise at 208 to a soln. of alcohol 14 (5.9 g, 47 mmol) and [VO(acac)2] (186 mg, 0.7 mmol)
in toluene (80 ml). After 2 h at 208, the mixture was diluted with Et2O (120 ml) and extracted with sat. aq.
NaHCO3 soln. and H2O to neutrality. The org. phase was dried (Na2SO4) and concentrated and the
residue bulb-to-bulb distilled: pure 15 (62%). B.p. 788/4.8 mbar. IR: 3423, 2954, 2929, 2868, 1469, 1448,
1426, 1383, 1362, 1309, 1221, 1169, 1150, 1088, 1051, 1029, 1000, 984, 965, 922, 882, 868, 832, 804, 693, 662.
1H-NMR: 3.83 (s, 1 H); 3.38 (s, 1 H); 2.03 (br. s, OH); 1.89 (d, J ¼ 14.4, 1 H); 1.59 (d, J ¼ 14.4, 1 H); 1.40
(s, 3 H); 1.03 (s, 3 H); 1.00 (s, 3 H). 13C-NMR: 80.7 (d); 67.3 (d); 62.9 (s); 45.8 (t); 39.2 (s); 30.1 (q); 24.7
.
(q); 18.4 (q). MS: 142 (11, Mþ ), 127 (10), 109 (33), 85 (100), 72 (33), 57 (41), 55 (35), 43 (65), 41 (38).
1,4,4-Trimethylcyclopentane-1,2,3-triol (16). A soln. of epoxy alcohol 15 (4.1 g, 29 mmol) in Et2O
(50 ml) was washed with 15% aq. HCl soln. (3 ꢁ 30 ml) and then with sat. aq. NH4Cl soln. to neutrality.
The org. phase was dried (MgSO4) and concentrated and the residue bulb-to-bulb distilled: 16 (21%).

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Helvetica Chimica Acta – Vol. 93 (2010)
B.p. 738/1.3 mbar. IR: 3395, 2961, 2933, 2870, 1700, 1656, 1469, 1448, 1407, 1378, 1366, 1306, 1259, 1224,
1202, 1140, 1093, 1028, 1011, 990, 948, 894, 854, 781, 698, 657. 1H-NMR: 4.26 (d, J ¼ 4.4, 1 H); 4.09 (d, J ¼
4.4, 1 H); 2.76 (br. s, 3 H); 2.11 (s, 2 H); 1.64 (s, 3 H); 1.21 (s, 3 H); 1.02 (s, 3 H). 13C-NMR: 82.9 (d); 80.3
.
(d); 74.4 (s); 55.0 (t); 39.6 (s); 29.9 (q); 27.4 (q); 25.3 (q). MS: 160 (1, Mþ ), 142 (7), 109 (9), 83 (11), 72
(100), 57 (17), 43 (14).
4,5-Dihydroxy-2,2,4-trimethylcyclopentanone (17). A mixture of epoxy ketone 10 (200 mg,
1.4 mmol) in 0.2% H2SO4 soln. (0.9 ml) was heated to reflux for 1 h. The mixture was diluted with
H2O (10 ml) and extracted with CH2Cl2 (3 ꢁ 10 ml). The org. phase was dried (Na2SO4) and
concentrated and the residue purified by CC (SiO2 ; cyclohexane/Et2O 95 :5): pure 17 (15%). White
crystals. IR: 3358, 3270, 2974, 2963, 2931, 2866, 2843, 1742, 1464, 1448, 1389, 1378, 1359, 1315, 1302, 1231,
1182, 1144, 1102, 1058, 1033, 1001, 952, 945, 892, 827, 795, 678. 1H-NMR: 4.53 (s, 1 H); 3.53 (br. s, OH);
3.26 (br. s, OH); 2.11 (d, J ¼ 13.5, 1 H); 2.00 (d, J ¼ 13.5, 1 H); 1.22 (s, 3 H); 1.19 (s, 3 H); 1.13 (s, 3 H).
.
13C-NMR: 219.2 (s); 82.6 (d); 75.3 (s); 48.3 (t); 42.0 (s); 28.8 (q); 25.4 (q); 22.4 (q). MS: 158 (21, Mþ ),
140 (48), 125 (35), 101 (100), 88 (42), 74 (42), 55 (32), 43 (60), 41 (30).
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Received June 12, 2009