Enantioselective synthesis of mono- and disubstituted 3, 6-dihydro-2H-pyrans and 5,6-dihydropyran-2-ones

Article abstract of DOI:10.3987/COM-03-9815

An enantioselective synthesis of mono- and disubstituted 3,6-dihydro-2H-pyrans and 5,6-dihydropyran-2-ones was achieved via ring-closing olefin metathesis, employing Grubb's catalyst, and starting from ready available chiral building blocks.

Full text of DOI:10.3987/COM-03-9815

HETEROCYCLES, Vol. 60, No. 9, 2003, pp. 2057 - 2063
Received, 26th May, 2003, Accepted, 15th July, 2003, Published online, 4th August, 2003
ENANTIOSELECTIVE
SYNTHESIS
OF
MONO-
AND
DISUBSTITUTED 3,6-DIHYDRO-2H-PYRANS AND 5,6-DIHYDRO-
PYRAN-2-ONES
Irene Izzo,* Pasquale Del Gaudio, Carmela Della Monica, Maria Squitieri,
and Francesco De Riccardis*
Department of Chemistry, University of Salerno, Via S. Allende –84081–
Baronissi, (SA), Italy
Abstract- An enantioselective synthesis of mono- and disubstituted 3,6-
dihydro-2H-pyrans and 5,6-dihydropyran-2-ones was achieved via ring-
closing olefin metathesis, employing Grubb’s catalyst, and starting from
ready available chiral building blocks.
Dihydro-2H-pyran and dihydropyran-2-one subunits are present in many biologically active natural
products showing potent cytotoxic, antiviral, thrombopoietic activities. Some examples are: elactocin,1
cytostatin,2 leptomycins,3 nafuredin,4 pironetin,5 and leustroducsins.6 In addition these compounds could
be useful building blocks for the synthesis of biologically active oxygen heterocycles via functionalization
of double bond.7 Recently many efforts have been directed towards stereoselective synthesis of 2,6-
difunctionalised di- and tetrahydropyrans8 and of α-hydroxyalkyldihydropyrans which have been used as
key intermediates in the synthesis of higher-order sugars such as (+)-3-deoxy-D-glycero-D-galacto-2-
nonulosonic acid (KDN), possessing oncofoetal antigen properties,9 and 2-deoxy-β-KDO, the most potent
inhibitor of the enzyme CMP-KDO synthetase.10
To date, however, there has been no demonstration of a general enantioselective method for the synthesis
of stereochemically defined mono- and disubstituted 3,6-dihydro-2H-pyrans (1) and 5,6-dihydropyran-2-
ones (2).11
(R)H
R1
O
(R)H
R1
O
O
1
2
With the aim of finding the most convenient and useful access to the above reported substructures, we
explored the potential of the ring-closing olefin metathesis on readily available derivatives of the

stereochemically pure starting materials (3-5). These valuable intermediates can be easily synthesized, in
both the enantiomeric forms, through stereospecific oxirane ring opening12 and straightforward functional
groups transformation,13 starting from cis- and trans-4-benzyloxy-2,3-epoxybutan-1-ols (6 and 7).14
OH
OH
OH
O
O
H
H
BnO
H
BnO
BnO
BnO
OH
H
OH
5
6
7
4
3
OTBDPS
OTBDPS
OTBDPS
Treatment of derivatives (3-5) with allyl bromide15 and acryloyl chloride 16 gave the allyl ethers (8-10) and
the acryloyl esters (11-13) in excellent yields.
O
O
O
BnO
BnO
9
10
8
OTBDPS
OTBDPS
OTBDPS
O
O
O
O
O
O
BnO
BnO
13
12
11
OTBDPS
OTBDPS
OTBDPS
Allyl ethers (8-10) and acrylates (11-13) were exposed to Grubb’s catalyst,17 bis-
(tricyclohexylphosphine)benzylidene ruthenium(IV) dichloride, RuCl2(CHC6H5)[P(C6H11)3]2, affording
the expected mono- and disubstituted 3,6-dihydro-2H-pyrans (14-16) and 5,6-dihydropyran-2-ones (17-19)
in high yields. No improvements in reaction times were observed adding to the reaction mixture titanium
isopropoxide (0.3-3 equiv.), even though has been reported that its presence increases yields of α,β-
unsatured γ- and δ-lactones and reduces the reaction times.15,18
O
O
O
BnO
BnO
15
16
14
OTBDPS
O
OTBDPS
O
OTBDPS
O
O
O
O
BnO
BnO
19
18
17
OTBDPS
OTBDPS
OTBDPS
In conclusion we have developed an efficient and general method for the enantioselective synthesis of
orthogonally protected optically active mono- and disubstituted 3,6-dihydro-2H-pyrans and 5,6-
dihydropyran-2-ones.

EXPERIMENTAL
Compounds (8-10). General procedure.
To a solution of alcohol (4) (0.143 g, 0.310 mmol) in CH2Cl2 (2 mL) at 0°C, Ag2O (0.159 g, 0.931 mmol)
was added. The mixture was stirred for 15 min at 0°C then allyl bromide (0.160 mL, 1.86 mmol). The
resulting mixture was stirred at 0°C for 0.5 h and at rt for 18 h. Centrifugation afforded an organic phase
which was concentraded in vacuo and purified by flash chromatography (silica gel, 10-30 % ethyl ether in
petroleum ether) to give 9 as a colorless oil (0.155 g).
Compound (8): oil, 96% yield; [α]D –4.8° (c = 1.0, CHCl ); 1H-NMR (400.13 MHz, CDCl3) δ 1.06 (9 H,
3
s, (CH3)3C-Si-), 2.56 (1 H, m, H-2), 3.52 (1 H, dd, J = 9.2, 3.0 Hz, H-1), 3.62 (1 H, dd, J = 9.2, 2.8 Hz, H’-
1), 3.74 (2 H, m, -CH2-OTBDPS), 3.99 (2 H, m, –OCH2–CH=CH2), 5.01-5.11 (3 H, d, H-4, H’-4 and –
CH=CHH, overlapped), 5.18 (1 H, d, J = 17.2 Hz, –CH=CHH), 5.76 (1 H, m, H-3), 5.83 (1 H, m, –
CH=CH2), 7.35-7.42 (6 H, m, -C6H5), 7.67 (4 H, m, -C6H5); 13C-NMR (100.06 MHz, CDCl3), δ 19.9, 27.4
(× 3), 46.8, 64.6, 70.9, 72.6, 117.1, 117.2, 128.2 (× 4), 130.1 (× 2), 134.3 (× 2), 135.6, 136.2 (× 4), 137.9.
EIMS m/z 380; Anal. Calcd for C24H32O2Si: C, 75.74; H, 8.47; Si, 7.38. Found: C, 75.89; H, 8.39; Si,
7.36.
Compound (9): oil, 95% yield; [α]D –9.1° (c = 1.0, CHCl ); 1H-NMR (400.13 MHz, CDCl3) δ 1.07 (9 H,
3
s, (CH3)3C-Si-), 2.51 (1 H, m, H-3), 3.51 (1 H, dd, J = 10.5, 6.0 Hz, H-1), 3.67 (1 H, dd, J = 10.5, 5.2 Hz,
H’-1), 3.75 (1 H, dd, J = 9.8, 4.5 Hz –CHHOTBDPS), 3.76 (1 H, m, H-2), 3.94 (1 H, dd, J = 9.8, 4.9 Hz -
CHH-OTBDPS), 4.05 (1 H, dd, J = 12.6, 5.6 Hz, –OCHH-CH=CH2), 4.25 (1 H, dd, J = 12.6, 5.5 Hz, -
OCHH-CH=CH2), 4.53 (2 H, s, OCH2Ph), 5.11 (3 H, d, H-5, H’-5 and –CH=CHH, overlapped), 5.24 (1 H,
d, J = 17.2 Hz, –CH=CHH), 5.90 (2 H, m, H-4 and –CH=CH2), 7.34-7.41 (11 H, m, -C6H5), 7.69 (4 H, m,
-C6H5); 13C-NMR (100.06 MHz, CDCl3), δ 19.3, 26.9 (× 3), 48.6, 64.0, 71.6 (× 2), 73.2, 77.7, 116.3,
117.1, 127.5 (× 7), 128.3 (× 2), 129.5 (× 2), 133.6, 133.7, 135.3, 135.6 (× 4), 137.0, 138.5. EIMS m/z 500;
Anal. Calcd for C32H40O3Si: C, 76.75; H, 8.05; Si, 5.61. Found: C, 76.72; H, 8.00; Si, 5.64.
Compound (10): oil, 78% yield; [α]D –11.1° (c = 1.0, CHCl ); 1H-NMR (400.13 MHz, CDCl3) δ 1.07 (9
3
H, s, (CH3)3C-Si), 2.51 (1 H, m, H-3), 3.51 (1 H, dd, J = 9.8, 5.0 Hz, H-1), 3.58 (1 H, dd, J = 10.0, 6.6 Hz
–CHHOTBDPS), 3.61 (1 H, dd, J = 10.0, 5.7 Hz -CHH-OTBDPS), 3.84 (1 H, dd, J = 9.8, 8.7 Hz, H’-1),
3.98 (1 H, ddd, J = 8.7, 5.0, 3.3 Hz, H-2), 4.08 (1 H, dd, J = 12.8, 5.4 Hz, –OCHH-CH=CH2), 4.25 (1 H,
dd, J = 12.8, 5.5 Hz, -OCHH-CH=CH2), 4.50 (1 H, d, J = 12.1 Hz, –OCHHPh), 4.56 (1 H, d, J = 12.1 Hz,
–OCHHPh), 5.02 (1 H, dd, J = 17.2, 1.9 Hz, H-5), 5.07 (1 H, dd, J = 10.5, 1.8 Hz, H’-5), 5.12 (1 H, d, J =
10.3 Hz, –OCH2CH=CHH), 5.24 (1 H, d, J = 15.8 Hz, –OCH2CH=CHH), 5.74 (1 H, m, H-4), 5.90 (1 H,
m, –OCH2CH=CH2), 7.34-7.41 (11 H, m, -C6H5), 7.68 (4 H, m, -C6H5); 13C-NMR (100.06 MHz, CDCl3),
δ 19.3, 26.9 (× 3), 49.0, 64.0, 72.1, 72.3, 73.2, 76.0, 116.1, 118.0, 127.5, 127.6 (× 6), 128.3 (× 2), 129.6 (×

2), 133.7 (× 2), 135.1, 135.6 (× 5), 138.5. EIMS m/z 500; Anal. Calcd for C32H40O3Si: C, 76.75; H, 8.05;
Si, 5.61. Found: C, 76.69; H, 8.01; Si, 5.61.
Compounds (11-13). General procedure.
To a solution of 4 (0.080 g, 0.174 mmol) in CH2Cl2 (2 mL) at –78°C, DMAP (0.004 g, 0.034 mmol), (i-
Pr)2NEt (0.210 mL, 1.21 mmol) and acryloyl chloride (0.056 mL, 0.694 mmol) were added. The resulting
mixture was stirred at –20° for 18 h, quenched with HCl (2 mL, 2 M), washed with a saturated solution of
NaHCO3. The organic phase was dried (Na2SO4), filtered and concentrated in vacuo. The residue was
purified by flash chromatography (silica gel 10-30% ethyl ether in petroleum ether) to give 12 as a
colorless oil (0.092 g)
Compound (11): oil, 96% yield; [α]D –4.1° (c = 1.0, CHCl ); 1H-NMR (400.13 MHz, CDCl3) δ 1.07 (9 H,
3
s, (CH3)3C-Si-), 2.66 (1 H, m, H-2), 3.73 (2 H, m, –CH2OTBDPS), 4.34 (2 H, m, H-1, H’-1), 5.13 (1 H, d,
J = 11.8 Hz, H-4 ), 5.14 (1 H, d, J = 16.0 Hz, H’-4 ), 5.79 (1 H, m, H-3), 5.80 (1 H, d, J = 10.4 Hz, –
CH=CHH), 6.09 (1 H, dd, J = 17.2, 10.4 Hz, –CH=CH2), 6.36 (1 H, d, J = 17.2 Hz, –CH=CHH), 7.36-7.43
13
(6 H, m, -C6H5), 7.67 (4 H, m, -C6H5); C-NMR (100.06 MHz, CDCl3), δ 19.3, 26.8 (× 3), 45.1, 63.7,
64.2, 117.4, 127.7 (× 4), 128.5, 129.6 (× 2), 130.5, 133.5 (× 2), 135.6, (× 4), 135.8, 166.0. EIMS m/z 394;
Anal. Calcd for C24H30O3Si: C, 73.05; H, 7.66; Si, 7.12. Found: C, 73.00; H, 7.69; Si, 7.10.
Compound (12): oil, 96% yield; [α]D –2.0° (c = 1.0, CHCl ); 1H-NMR (400.13 MHz, CDCl3) δ 1.02 (9 H,
3
s, (CH3)3C-Si-), 2.74 (1 H, m, H-3), 3.63 (1 H, dd, J = 10.9, 5.4 Hz, H-1), 3.67 (1 H, dd, J = 9.9, 4.2 Hz, –
CHHOTBDPS), 3.70 (1 H, dd, J = 10.9, 2.9 Hz, H’-1), 3.76 (1 H, dd, J = 9.9, 4.9 Hz, –CHHOTBDPS),
4.43 (1 H, d, J = 12.0 Hz, –OCHHPh), 4.55 (1 H, d, J = 12.0 Hz, –OCHHPh), 5.14 (1 H, d, J = 10.8 Hz,
H-5 ), 5.15 (1 H, d, J = 16.8 Hz, H’-5), 5.34 (1 H, m, H-2), 5.81 (1 H, d, J = 10.7 Hz, –CH=CHH), 5.86 (1
H, m, H-3), 6.11 (1 H, dd, J = 17.3, 10.7 Hz, –CH=CH2), 6.37 (1 H, d, J = 17.3 Hz, –CH=CHH), 7.33-7.43
13
(11 H, m, -C6H5), 7.62 (4 H, m, -C6H5); C-NMR (100.06 MHz, CDCl3), δ 19.2, 26.7 (× 3), 47.0, 63.6,
69.6, 72.1, 73.0, 118.2, 127.6 (× 7), 128.3 (× 2), 128.6, 129.5 (× 2), 130.7, 133.3 (× 2), 134.0, 135.6, (× 4),
137.1, 166.1. EIMS m/z 514; Anal. Calcd for C32H38O4Si: C, 74.67; H, 7.44; Si, 5.46. Found: C, 74.60; H,
7.37; Si, 5.45.
Compound (13): oil, 84% yield; [α]D –7.7° (c = 1.0, CHCl ); 1H-NMR (400.13 MHz, CDCl3) δ 1.07 (9 H,
3
s, (CH3)3C-Si-), 2.71 (1 H, m, H-3), 3.60 (2 H, m, H-1 and H’-1), 3.73 (2 H, m, –CH2OTBDPS), 4.50 (1
H, d, J = 12.0 Hz, –OCHHPh), 4.55 (1 H, d, J = 12.0 Hz, –OCHHPh), 5.12 (1 H, d, J = 17.2 Hz, H-5 ),
5.14 (1 H, d, J = 10.3 Hz, H’-5), 5.56 (1 H, m, H-2), 5.76 (1 H, m, H-4), 5.83 (1 H, d, J = 10.0 Hz, –
CH=CHH), 6.13 (1 H, dd, J = 17.2, 10.0 Hz, –CH=CH2), 6.40 (1 H, d, J = 17.2 Hz, –CH=CHH), 7.36-
13
7.43 (11 H, m, -C6H5), 7.65 (4 H, m, -C6H5); C-NMR (100.06 MHz, CDCl3), δ 19.2, 26.8 (× 3), 47.3,
63.7, 69.4, 71.2, 72.9, 118.8, 127.7 (× 7), 128.4 (× 2), 128.6, 129.6 (× 2), 130.7, 133.3, 133.4, 134.6,

135.6, (× 4), 138.1, 165.5. EIMS m/z 514; Anal. Calcd for C32H38O4Si: C, 74.67; H, 7.44; Si, 5.46. Found:
C, 74.65; H, 7.41; Si, 5.45.
Compounds (14-16). General procedure.
To a solution of the allyl ether (9) (0.030 g, 0.060 mmol) in degassed CH2Cl2 (10 mL), Grubb’s catalyst
(0.010 g, 0.012 mmol) was added. The resulting mixture was stirred at reflux for 24 h. The mixture was
then cooled to rt, concentrated in vacuo. The residue was purified by flash chromatography (silica gel, 50-
100% CH2Cl2 in petroleum ether) to give 15 as a colorless oil (0.028 g).
Compound (14): oil, 98% yield; [α]D +49.9° (c = 0.8, CHCl ); 1H-NMR (400.13 MHz, CDCl3) δ 1.06 (9
3
H, s, (CH3)3C-Si-), 2.44 (1 H, m, H-3), 3.63 (2 H, m, -CH2-OTBDPS), 3.77 (1 H, dd, J = 11.1, 5.8 Hz, H-
2), 3.88 (1 H, dd, J = 11.1, 5.7 Hz, H’-2), 4.09 (2 H, m, H-6, H’-6), 5.69 (1 H, br d, J = 10.7 Hz, H-4 or
H-5), 5.77 (1 H, d, J = 10.7 Hz, H-5 or H-4), 7.30-7.44 (6 H, m, -C6H5), 7.66 (4 H, m, -C6H5); 13C-NMR
(100.06 MHz, CDCl3), δ 19.2, 26.8 (× 3), 37.8, 64.7, 65.6, 66.3, 125.3, 127.6 (× 4), 127.8, 129.6 (× 2),
133.7 (× 2), 135.6 (× 4); EIMS m/z 352; Anal. Calcd for C22H28O3Si: C, 74.95; H, 8.01; Si, 7.97. Found:
C, 74.89; H, 8.00; Si, 7.94.
Compound (15): oil, 100% yield; [α]D +86.7° (c = 1.0, CHCl3); 1H-NMR (400.13 MHz, CDCl ) δ 1.03 (9
3
H, s, (CH3)3C-Si-), 2.28 (1 H, m, H-3), 3.51 (1 H, dd, J = 10.4, 4.9 Hz, -CHH-OTBDPS), 3.72 (2 H, m, -
CH2-OBn), 3.80 (1 H, dd, J = 10.4, 8.2 Hz, -CHH-OTBDPS), 3.91 (1 H, m, H-2), 4.23 (2 H, m, H-6, H’-
6), 4.49 (1 H, d, J = 12.3 Hz, CHH-Ph), 4.65 (1 H, d, J = 12.3 Hz, CHH-Ph), 5.71 (2 H, m, H-4, H-5),
13
7.29-7.44 (9 H, m, -C6H5), 7.63 (6 H, m, -C6H5); C-NMR (100 MHz, CDCl3) δ 19.0, 26.7 (× 3), 39.6,
62.7, 66.3, 71.6, 73.4, 75.5, 125.6, 127.7 (× 8), 128.3 (× 2), 129.6 (× 2), 133.4 (× 2), 135.5 (× 4), 138.3;
EIMS m/z 472; Anal. Calcd for C30H36O3Si: C, 76.23; H, 7.68; Si, 5.94. Found: C, 76.20; H, 7.69; Si,
5.87.
Compound (16): oil, 70% yield; [α]D +26.0° (c = 1.0, CHCl ); 1H-NMR (400.13 MHz, CDCl3) δ 1.04 (9
3
H, s, (CH3)3C-Si-), 2.41 (1 H, m, H-3), 3.54 (2 H, m, -CH2-OTBDPS), 3.64 (2 H, m, -CH2-OBn), 3.76 (1
H, m, H-2), 4.16 (1 H, br d, J = 17.3 Hz, H-6), 4.26 (1 H, br d, J = 17.3 Hz, H’-6), 4.56 (2 H, br s, -CH2-
Ph), 5.73 (1 H, br d, J = 9.7 Hz, -H-4), 5.83 (2 H, br d, J = 9.7 Hz, H-5), 7.30-7.43 (9 H, m, -C6H5), 7.66 (4
H, m, -C6H5); 13C-NMR (100.06 MHz, CDCl3) δ 19.3, 26.8 (× 3), 38.8, 64.7, 64.8, 71.2, 73.4, 74.8, 126.0,
127.1, 127.5, 127.7 (× 6), 128.3 (× 2), 129.7 (× 2), 133.4, (× 2), 135.6 (× 4), 138.2; EIMS m/z 472; Anal.
Calcd for C30H36O3Si: C, 76.23; H, 7.68; Si, 5.94. Found: C, 76.25; H, 7.65; Si, 5.87.
Compounds (17-19). General procedure.
To a solution of the acrylate (12) (0.041 g, 0.080 mmol) in degassed CH2Cl2 (17 mL), Grubb’s catalyst
(0.023 g, 0.028 mmol) was added. The resulting mixture was stirred at reflux for 48-76 h. The mixture was

then cooled to rt, concentrated in vacuo. The residue was purified by flash chromatography (silica gel, 90-
100% of CH2Cl2 in petroleum ether) to give 18 as a colorless oil (0.039 g).
Compound (17): oil, 95% yield; [α]D +11.5° (c = 1.0, CHCl3); 1H-NMR (400.13 MHz, CDCl3) δ 1.02 (9
H, s, (CH3)3C-Si), 2.73 (1 H, m, H-5), 3.68 (2 H, m, -CH2-OTBDPS), 4.42 (2 H, m, H-6, H’-6), 6.01 (1 H,
d, J = 9.8 Hz, H-3), 6.77 (1 H, dd, J = 9.8, 3.7 Hz, H-4), 7.38-7.47 (6 H, m, -C6H5), 7.62 (4 H, m, -C6H5);
13C-NMR (100.06 MHz, CDCl3) δ 19.2, 26.7 (× 3), 36.9, 62.5, 68.3, 122.0, 127.8 (× 4), 130.0 (× 2), 132.7,
132.8, 135.5 (× 4), 146.7, 163.5; EIMS m/z 366; IR (CHCl3): υ = 1720 cm-1 (C=O); Anal. Calcd for
C22H26O3Si: C, 76.09; H, 7.15; Si, 7.66. Found: C, 76.04; H, 7.17; Si, 7.67.
Compound (18): oil, 90% yield; [α]D +94.3° (c = 1.0, CHCl3); 1H-NMR (400.13 MHz, CDCl3) δ 1.02 (9
H, s, (CH3)3C-Si), 2.70 (1 H, m, H-5), 3.66 (4 H, overlapped, CH2-OBn, and CH2-OTBDPS), 4.43 (1 H, d,
J = 11.8 Hz, -CHH-Ph), 4.52 (1 H, d, J = 11.8 Hz, -CHH-Ph), 4.72 (1 H, m, H-6), 6.05 (1 H, br d, J = 9.5
Hz, H-3), 6.87 (1 H, dd, J = 9.5, 5.9 Hz, H-4), 7.29-7.39 (11 H, m, -C6H5), 7.60 (4 H, m, -C6H5); 13C-NMR
(100.06 MHz, CDCl3) δ 19.0, 26.7 (× 3), 38.2, 60.9, 69.1, 73.5, 77.8, 121.9, 127.8 (× 7), 128.4 (× 2), 129.9
(× 2), 132.7 (× 2), 135.4 (× 4), 137.5, 146.9, 163.5; EIMS m/z 486; IR (CHCl3): υ = 1720 cm-1 (C=O);
Anal. Calcd for C30H34O4Si: C, 74.04; H, 7.04; Si, 5.77. Found: C, 74.02; H, 7.10; Si, 5.77.
Compound (19): oil, 100% yield; [α]D +43.6° (c = 1.0, CHCl3); 1H-NMR (400.13 MHz, CDCl3) δ 1.04 (9
H, s, (CH3)3C-Si-), 2.89 (1 H, m, H-5), 3.56 (1 H, dd, J = 10.9, 3.8 Hz, -CHH-OBn), 3.67 (1 H, dd, J =
10.3, 1.9 Hz, -CHH-OTBDPS), 3.68 (1 H, br d, J = 10.9, -CHH-OBn), 3.80 (1 H, dd, J = 10.3, 5.0 Hz, -
CHH-OTBDPS), 4.46 (1 H, d, J = 12.0 Hz, -CHH-Ph), 4.54 (1 H, d, J = 12.0 Hz, -CHH-Ph), 4.65 (1 H,
m, H-6), 6.03 (1 H, dd, J = 10.0, 2.1 Hz, H-3), 6.78 (1 H, dd, J = 10.0, 3.1 Hz, H-4), 7.26-7.43 (11 H, m, -
13
C6H5), 7.60 (4 H, m, -C6H5); C-NMR (100.06 MHz, CDCl3) δ 19.2, 26.8 (× 3), 37.8, 62.8, 69.2, 73.5,
78.0, 121.8, 127.6, 127.9 (× 6), 128.4 (× 2), 130.0 (× 2), 132.7, 132.8, 135.5 (× 4), 137.6, 147.6, 163.3.
EIMS m/z 486; IR (CHCl3): υ = 1730 cm-1 (C=O); Anal. Calcd for C30H34O4Si: C, 74.04; H, 7.04; Si,
5.77. Found: C, 74.04; H, 7.07; Si, 5.66.
ACKNOWLEDGMENTS
This work has been supported by the MIUR (“PRIN: Chimica dei Composti Organici di Interesse
Biologico”) and by the Università degli Studi di Salerno.
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