Reductive ring opening of oxygen-containing benzo-fused heterocycles by an arene-catalysed lithiation

Article abstract of DOI:10.1055/s-2004-815971

The reductive ring opening of phthalan and isochroman in a 8 mmol scale process, using a small excess of lithium (1.35 equiv) and a substoichiometric amount of DTBB (3 mol%), leads to functionalised organolithium compounds, which after reaction with (-)-m

Full text of DOI:10.1055/s-2004-815971

PRACTICAL SYNTHETIC PROCEDURES
1115
Reductive Ring Opening of Oxygen-Containing Benzo-Fused Heterocycles by
an Arene-Catalysed Lithiation
R
eductive Ring Openin
i
g Of
O
g
xygen-Cont
u
a
ining Benzo
e
-
Fused Het
l
erocycles Yus,* Benjamín Moreno, Francisco Foubelo
Departamento de Química Orgánica, Facultad de Ciencias and Instituto de Síntesis Orgánica (ISO),
Universidad de Alicante, Apdo. 99, 03080 Alicante, Spain
Fax +34(965)903549; E-mail: yus@ua.es
PSP
Received 29 December 2003
No20
Abstract: The reductive ring opening of phthalan and isochroman in a 8 mmol scale process, using a small excess of lithium (1.35 equiv)
and a substoichiometric amount of DTBB (3 mol%), leads to functionalised organolithium compounds, which after reaction with (–)-men-
thone as electrophile followed by hydrolysis with water, gives the corresponding diols in good yields with high stereoselectivity. Dehydra-
tion of these diols leads to the corresponding oxygen-containing heterocycles, which are homologous of the starting heterocycles.
Key words: functionalised organolithium compounds, stereoselective addition, reductive opening, lithiation
1)
, -78 to -20 ºC
MsCl, Et3N
Li
O
3
Li, DTBB (3%)
O
( )n
OH
O
2) H2O, -20 ºC
( )n
OLi
( )n
( )n
OH
1a (n = 1)
1b (n = 2)
2
4a (76%)
4b (68%)
5a (78%)
5b (55%)
Scheme 1
Functionalised organolithium compounds1 can be pre- Benzylic carbon–oxygen bonds are susceptible of suffer-
pared following the same methodologies as for simple or- ing reductive cleavage by means of lithium metal to gen-
ganolithium compounds and are of interest in synthetic erate benzylic organolithium compounds. Phthalan (1a)
organic chemistry because polyfunctionalised molecules and isochroman (1b) are a special kind of cyclic benzyl
are obtained in only one step by reaction with electro- ethers. These heterocycles are opened reductively with
philic reagents.2 In the case of these functionalised inter- lithium and a catalytic amount of DTBB at 0 and 20 °C,
mediates, one of the most elegant and direct strategies respectively, to afford dianions 2 which have shown a
consists in the reductive opening of appropriate oxygen-, wide use in organic synthesis.13,14 The reaction of interme-
nitrogen- and sulfur-containing heterocycles.3 However, diates 2 with (–)-menthone (3) as electrophile at –78 °C
the following requirements should be accomplished in or- gave the diols 4, after hydrolysis with water at the same
der to achieve the reductive opening of a heterocycle: (a) temperature (Scheme 1). Regarding the stereochemistry
small heterocycles (three- and four-membered rings) due of these reaction products, the almost exclusive diastere-
to release of strain energy3 and (b) heterocycles with acti- omers are those resulting from the attack of dianions 2 to
vated bonds that can be reductively broken by means of the less hindered face of the carbonyl group. The diastere-
1
the lithiating reagent, as in the case of compounds bearing omeric ratios were determined by the study of the H
allylic4 and benzylic5 carbon–heteroatom bonds as well as NMR spectra of the crude reaction mixtures, being around
cyclic aryl ethers6 and thioethers.7 Concerning the lithia- 30:1 for phthalan derivative 4a and 22:1 in the case of iso-
tion process, one potent lithiating mixture, which has chroman derivative 4b. Finally, dehydration of diols 4 led
shown to be very effective even at low temperatures, con- to the homologous spiro heterocyclic compounds 5. All
sists in the use of an excess of lithium in the presence of a attempts to perform the dehydration under acidic condi-
catalytic amount of an arene,8 naphthalene and 4,4¢-di- tions gave always a mixture of diastereomers due to
tert-butylbiphenyl (DTBB), and these are most commonly epimerisation of the new stereogenic center. However, to-
used.9 More recently, polymer supported naphthalene, tal retention of the configuration was obtained when the
biphenyl10 and also polyphenylene11 have been used as diols 4 were treated with an excess of methanesulfonyl
electron-transfer reagents in these processes.12
chloride in the presence of triethylamine in dichlo-
romethane. The configuration of the new stereogenic cen-
ter for the major isomers was confirmed by a NOESY
experiment in compound 5b. NOE is observed between
one of the diastereotopic protons at benzylic position
[2.35 ppm (d, J = 14.2 Hz)] and the axial proton next to
SYNTHESIS 2004, No. 7, pp 1115–1118
x
x
.
x
x
.2
0
0
4
Advanced online publication: 12.02.2004
DOI: 10.1055/s-2004-815971; Art ID: Z19003SS
© Georg Thieme Verlag Stuttgart · New York

1116
M. Yus et al.
PRACTICAL SYNTHETIC PROCEDURES
the new stereogenic center which appear at 0.44 ppm as a oids (estrone and cholestanone)16 gives the expected
dd (J = 12.2, 12.35 Hz) (Figure 1).
selectively functionalised natural products.
As commented above, the functionalised organolithium
compounds 2 have been used extensively in organic syn-
thesis. Thus, the reaction of the organolithium intermedi-
ate 2b with equimolecular amounts of zinc bromide and
copper cyanide, followed by treatment with 1,4-dibro-
mobut-2-ene leads, after hydrolysis, almost exclusively to
the corresponding alcohol 10 resulting from a SN2¢ dis-
placement, the process being highly regioselective
(Scheme 2).17 The reaction of 2a with an electrophilic ole-
fin such as benzylidenacetone in the presence of copper(I)
salts and HMPA in THF at –78 °C leads, after hydrolysis
with a saturated solution of ammonium chloride, to the
hydroxy ketone 11, resulting from a conjugate addition
(Scheme 2).18,19 The palladium-catalysed Negishi cross-
coupling reaction can also be applied to the in situ gener-
ated functionalised organozinc reagent, which are easily
prepared from functionalised organolithium 2a by a lithi-
um-zinc transmetallation process with zinc bromide. This
reaction is not possible without the help of both the zinc
and palladium components, the process working well for
arylic and vinylic bromides, as well as with iodides. In the
case of p-(trifluoromethyl)phenyl bromide, compound 12
is obtained in good yield (Scheme 2).20,21 Finally,
chemoselective acylation can be easily achieved using a
tandem reaction of intermediate 2b with acetic anhydride
and propanoyl chloride, after generating the correspond-
ing zinc-copper species, to give compound 13
(Scheme 2).22
NOE
H
H
H
O
5b
Figure 1 NOE enhancement for 5b
At this point it is worthy to note the advantage of working
on a larger scale (8 mmol) compared to the process per-
formed at 1 mmol scale. Due to the low density of lithium
powder in the reaction medium, in the small scale process
an important amount of the metal is lost on the walls of the
flask, so a large excess (ca. 15:1, lithium:substrate molar
ratio) is needed. On the contrary for the 8 mmol scale,
only a 2.5:1 molar ratio was necessary to carry out the
lithiation step.
The lithiation of 1a can be directed to the introduction of
two different electrophiles at both benzylic positions in a
sequential manner. Thus, if after addition of pentan-3-one
as the first electrophile, the resulting alcoholate 6 is stirred
in the presence of the excess of lithiating mixture at room
temperature for four additional hours, a new organolithi-
um intermediate 8 is formed, which by reaction with car-
bon dioxide as a second electrophile, yields, after acidic
hydrolysis, the hydroxy acid 9.13 On the other hand, the
hydrolysis of the dialcoholate 6 leads to the diol 7
(Scheme 2).13 The use of keto derivatives of some protect-
ed monosaccharides (glucose, fructose),15 as well as ster-
All reactions were carried out under argon in oven-dried glassware.
All reagents were commercially available and were used as re-
ceived. THF was distilled from sodium benzophenone ketyl. IR
spectra were measured (neat) with a Nicolet Impact 400 D-FT Spec-
Ph
OH
O
11
(58%)
1) PhCH=CHCOCH3, CuI
[n = 1]
2) NH4Cl
1) BrCH2CH=CHCH2Br
ZnBr2, CuCN
Li
Et2CO
[n = 1]
H2O
OLi
OLi
OH
OH
2) HCl, H2O
[n = 2]
( )n
Br
OLi
OH
10
(49%)
7
2a (n = 1)
2b (n = 2)
6
(74%)
1) ZnBr2, CuCN·LiCl
2) (MeCO)2O
Li, DTBB (3%)
1) ZnBr2
[n = 1] 2) 4-CF3C6H4Br, Pd(PPh3)4
3) EtCOCl
[n = 2]
4) H2O
3) H2O
1) CO2
OLi
OH
O
O
2) HCl, H2O
CF3
O
OH
Li
CO2H
12
(67%)
8
9
13
(53%)
(41%)
Scheme 2
Synthesis 2004, No. 7, 1115–1118 © Thieme Stuttgart · New York

PRACTICAL SYNTHETIC PROCEDURES
Ring Opening of Benzo-Fused Heterocycles
1117
trometer. NMR spectra were recorded with a Bruker AC-300 using
CDCl3 as the solvent. 13C NMR DEPT was used to assign the C at-
oms. LRMS and HRMS were measured with Shimadzu GC/HS QP-
5000 and Finingan MAT95 S spectrometers, respectively. The pu-
rity of volatile products and the chromatographic analyses (GC)
were determined with a Hewlett-Packard HP-5890 instrument
equipped with a flame ionisation detector and a 12 m capillary col-
umn (0.2 mm diam., 0.33 mm film thickness), using N2 (2 mL/min)
as carrier gas, Tinjector = 275 °C, Tdetector = 300 °C, Tcolumn = 60 °C (3
min) and 60–270 °C (15 °C/min), P = 40 kPa. Specific rotations
were determined with a Perkin Elmer 341 digital polarimeter.
H), 2.50 (d, J = 13.7 Hz, 1 H), 2.93–3.10 (m, 2 H), 3.40 (d, J = 13.7
Hz, 1 H), 3.81–3.87 (m, 2 H), 7.11–7.25 (m, 4 H).
13C NMR (75 MHz, CDCl3): d = 18.0 (CH3), 20.8 (CH2), 22.3
(CH3), 23.7 (CH3), 26.0 (CH), 27.6 (CH), 35.0 (CH2), 35.6 (CH2),
42.3 (CH2), 46.8 (CH2), 50.7 (CH), 63.3 (CH2), 75.2 (C), 125.8
(CH), 126.5 (CH), 129.6 (CH), 132.3 (CH), 136.6 (C), 138.2 (C).
MS (EI, 70 eV): m/z (%) = 272 [M+ – (H2O), 1], 155 (57), 137 (34),
136 (32), 118 (36), 117 (22), 115 (11), 106 (25), 105 (21), 95 (41),
91 (20), 81 (100), 79 (10), 77 (13), 69 (44).
HRMS (EI): m/z calcd for C19H28O (M – H2O): 272.2140; found:
272.2116.
(1R,2S,5R)-1-(2-Hydroxymethylbenzyl)-2-isopropyl-5-methyl-
cyclohexanol (4a)
Spiro Compound 5a
To a blue suspension of lithium powder (150 mg, 21.4 mmol) and a
catalytic amount of DTBB (130 mg, 0.5 mmol; 3 mol%) in anhyd
THF (25 mL) under argon was added dropwise phthalan (1a; 960
mg, 0.88 mL, 8.0 mmol) at 0 °C, and the resulting mixture was
stirred for 6 h (monitored by GC) at the same temperature. Then, the
temperature was cooled down to –78 °C and (–)-menthone (3; 1.23
g, 1.56 mL, 8.0 mmol) was added dropwise. After that, the reaction
mixture was allowed to warm to –20 °C for around 3 h, hydrolysed
with H2O (10 mL), and extracted with EtOAc (3 × 40 mL). The
combined organic layers were dried (Na2SO4) and evaporated (15
Torr). The residue was purified by column chromatography (hex-
ane–EtOAc, 20:1, 85 g Merck silica gel 60, 0.063–0.200 mm) to
give 4a as a colourless oil (1.67 g, 76%); [a]D20 –19.5 (c = 1.0,
CH2Cl2); Rf 0.13 (hexane–EtOAc, 5:1).
To a solution of the diol 4a (276 mg, 1.0 mmol) in anhyd CH2Cl2 (3
mL) under argon was added dropwise first methanesulfonyl chlo-
ride (252 mg, 0.17 mL, 2.2 mmol) and then Et3N (222 mg, 0.30 mL,
2.2 mmol) at 0 °C. The reaction mixture was stirred for 4 h (moni-
tored by GC) at the same temperature. The mixture was then hydrol-
ysed with aq 2 M HCl (5 mL), the organic layer was neutralised with
an aq sat. solution of NaHCO3, washed with H2O (10 mL), extracted
with EtOAc (3 × 15 mL), and the organic layer was dried (Na2SO4)
and evaporated (15 Torr). The residue was purified by column chro-
matography (hexane, 30 g Merck silica gel 60, 0.063–0.200 mm) to
yield 5a as a colourless oil (201 mg, 78%); [a]D20 –29 (c = 0.42,
CH2Cl2); Rf 0.39 (hexane).
IR (film): 2951, 2918, 2853, 1732, 1454, 1072 1363 cm–1.
1H NMR (300 MHz, CDCl3): d = 0.67 (dd, J = 12.5, 14.0 Hz, 1 H),
0.81 (d, J = 6.7 Hz, 3 H), 0.87 (d, J = 6.9 Hz, 3 H), 0.93 (d, J = 7.0
Hz, 3 H), 1.17–1.32 (m, 2 H), 1.50–1.68 (m, 3 H), 1.70–1.82 (m, 1
H), 1.95–2.05 (m, 1 H), 2.16–2.22 (m, 1 H), 2.17 (d, J = 16.0 Hz, 1
H), 3.33 (d, J = 16.0 Hz, 1 H), 4.60–4.72 (m, 2 H), 6.99–7.02 (m, 1
H), 7.07–7.16 (m, 3 H).
13C NMR (75 MHz, CDCl3): d = 18.3 (CH3), 20.9 (CH2), 22.3
(CH3), 24.0 (CH3), 26.2 (CH), 27.9 (CH), 35.5 (CH2), 35.9 (CH2),
42.0 (CH2), 50.3 (CH), 62.0 (CH2), 75.2 (C), 123.9 (CH), 125.4
(CH), 126.3 (CH), 129.2 (CH), 134.0 (C), 134.9 (C).
IR (film): 3350, 2951, 2863, 1701, 1640, 1448 cm–1.
1H NMR (300 MHz, CDCl3): d = 0.81 (d, J = 6.2 Hz, 3 H), 0.87–
1.04 (m, 2 H), 0.98 (d, J = 7.02 Hz, 6 H), 1.21–1.51 (m, 4 H), 1.59–
1.67 (m, 1 H), 1.73–1.78 (m, 1 H), 2.35–2.45 (m, 1 H), 2.43 (d,
J = 13.9 Hz, 1 H), 2.71 (br s, 2 H), 3.61 (d, J = 13.9 Hz, 1 H), 4.42
(d, J = 11.9 Hz, 1 H), 4.81 (d, J = 11.9 Hz, 1 H), 7.14–7.27 (m, 3 H),
7.33–7.38 (m, 1 H).
13C NMR (75 MHz, CDCl3): d = 18.0 (CH3), 21.0 (CH2), 22.3
(CH3), 23.8 (CH3), 25.9 (CH), 28.0 (CH), 34.8 (CH2), 42.4 (CH2),
46.8 (CH2), 51.1 (CH), 63.3 (CH2), 74.7 (C), 126.9 (CH), 127.3
(CH), 130.6 (CH), 133.0 (CH), 136.0 (C), 140.5 (C).
MS (EI, 70 eV): m/z (%) = 258 (M+, 27), 173 (54), 146 (17), 145
(23), 117 (10), 105 (16), 104 (100), 103 (12), 78 (15), 69 (27).
MS (EI, 70 eV): m/z (%) = 258 [M+ – H2O, 3], 104 (100), 95 (11),
81 (29), 69 (21).
HRMS (EI): m/z calcd for C18H26O (M): 258.1984; found:
258.1978.
HRMS (EI): m/z calcd for C18H26O (M – H2O): 258.1984; found:
258.1971.
Spiro Compound 5b
To a solution of the diol 4b (290 mg, 1.0 mmol) in anhyd CH2Cl2 (3
mL) under argon was added dropwise first methanesulfonyl chlo-
ride (252 mg, 0.17 mL, 2.2 mmol) and then Et3N (222 mg, 0.30 mL,
2.2 mmol) at 0 °C. The reaction mixture was stirred for 1 h (moni-
tored by GC) at the same temperature. The reaction mixture was
then hydrolysed with aq 2 M HCl (5 mL), the organic layer was neu-
tralised with an aq sat. solution of NaHCO3, washed with H2O (10
mL), extracted with EtOAc (3 × 15 mL), and the organic layer was
dried (Na2SO4) and evaporated (15 Torr). The residue was purified
by column chromatography (hexane, 30 g Merck silica gel 60,
0.063–0.200 mm) to yield 5b as a colourless oil (149 mg, 55%);
[a]D20 –87.5 (c = 0.76, CH2Cl2); Rf 0.50 (hexane).
(1R,2S,5R)-1-[2-(2-Hydroxyethyl)benzyl]-2-isopropyl-5-meth-
ylcyclohexanol (4b)
To a blue suspension of lithium powder (150 mg, 21.4 mmol) and a
catalytic amount of DTBB (130 mg, 0.5 mmol; 3 mol%) in anhyd
THF (25 mL) under argon was added dropwise isochroman (1b;
1.07 g, 1.00 mL, 8.0 mmol) at 20 °C, and the resulting mixture was
stirred for 4 h (monitored by GC) at the same temperature. Then, the
temperature was cooled down to –78 °C and (–)-menthone (3; 1.23
g, 1.56 mL, 8.0 mmol) was added dropwise. After that, the reaction
mixture was allowed to warm to –20 °C for around 3 h, hydrolysed
with H2O (20 mL), and extracted with EtOAc (3 × 40 mL). The
combined organic layers were dried (Na2SO4) and evaporated (15
Torr). The residue was purified by column chromatography (hex-
ane–EtOAc, 20:1, 85 g Merck silica gel 60, 0.063–0.200 mm) to
yield 4b as a colourless oil (1.57 g, 68%); [a]D20 –29.2 (c = 1.1,
CH2Cl2); Rf 0.37 (hexane–EtOAc, 2:1).
IR (film): 2940, 2864, 1733, 1493, 1454 cm–1.
1H NMR (300 MHz, CDCl3): d = 0.44 (dd, J = 12.2, 12.35 Hz, 1 H),
0.71 (d, J = 6.5 Hz, 3 H), 0.79–0.89 (m, 1 H), 0.94 (d, J = 7.0 Hz, 3
H), 0.98 (d, J = 6.8 Hz, 3 H), 1.0–1.15 (m, 1 H), 1.39–1.73 (m, 5 H),
2.30–2.38 (m, 1 H), 2.35 (d, J = 14.2 Hz, 1 H), 2.60 (dd, J = 4.7 Hz,
15.0 Hz, 1 H), 3.16–3.26 (m, 1 H), 3.56 (t, J = 11.6 Hz, 1 H), 3.67
(d, J = 14.2 Hz, 1 H), 3.77–3.83 (m, 1 H), 6.97–7.25 (m, 4 H).
IR (film): 3375, 3060, 2946, 1722, 1596, 1454 cm–1.
1H NMR (300 MHz, CDCl3): d = 0.76 (d, J = 6.55 Hz, 3 H), 0.82–
0.95 (m, 1 H), 0.98 (d, J = 7.0 Hz, 3 H), 1.00 (d, J = 7.1, 3 H), 1.18–
1.58 (m, 6 H), 1.71–1.75 (m, 1 H), 2.07 (br s, 2 H), 2.32–2.41 (m, 1
13C NMR (75 MHz, CDCl3): d = 18.4 (CH3), 20.7 (CH2), 22.4
(CH3), 24.1 (CH3), 25.9 (CH), 26.9 (CH), 35.5 (CH2), 39.2 (CH2),
Synthesis 2004, No. 7, 1115–1118 © Thieme Stuttgart · New York

1118
M. Yus et al.
PRACTICAL SYNTHETIC PROCEDURES
39.6 (CH2), 47.7 (CH2), 53.7 (CH), 61.0 (CH2), 76.1 (C), 126.0
(CH), 126.1 (CH), 128.5 (CH), 130.0 (CH), 139.5 (C), 140.9 (C).
MS (EI, 70 eV): m/z (%) = 272 (M+, 13), 119 (40), 118 (100), 117
Fenude, E.; Rassu, G. J. Org. Chem. 1992, 57, 1444.
(f) Bachki, A.; Foubelo, F.; Yus, M. Tetrahedron Lett. 1998,
39, 7759. (g) Foubelo, F.; Yus, M. Tetrahedron Lett. 1999,
40, 743. (h) Foubelo, F.; Saleh, S. A.; Yus, M. J. Org. Chem.
2000, 65, 3478. (i) Ferrández, J. V.; Foubelo, F.; Yus, M.
Eur. J. Org. Chem. 2001, 3223. (j) Yus, M.; Foubelo, F.;
Ferrández, J. V.; Bachki, A. Tetrahedron 2002, 58, 4907.
(7) (a) Screttas, C. G.; Micha-Screttas, M. J. Org. Chem. 1978,
43, 1064. (b) Screttas, C. G.; Micha-Screttas, M. J. Org.
Chem. 1979, 44, 713. (c) Cohen, T.; Bhupathy, M. Acc.
Chem. Res. 1989, 22, 152. (d) Foubelo, F.; Gutiérrez, A.;
Yus, M. Tetrahedron Lett. 1997, 38, 4837. (e) Foubelo, F.;
Gutiérrez, A.; Yus, M. Synthesis 1999, 503. (f) Foubelo, F.;
Gutiérrez, A.; Yus, M. Tetrahedron Lett. 1999, 40, 8173.
(g) Foubelo, F.; Gutiérrez, A.; Yus, M. Tetrahedron Lett.
1999, 40, 8177. (h) Foubelo, F.; Yus, M. Tetrahedron Lett.
2000, 41, 5335. (i) Gutiérrez, A.; Foubelo, A.; Yus, M.
Tetrahedron 2001, 57, 4411. (j) Yus, M.; Foubelo, F.;
Ferrández, J. V. Chem. Lett. 2002, 726. (k) Yus, M.;
Foubelo, F.; Ferrández, J. V. Tetrahedron Lett. 2002, 43,
7205. (l) Yus, M.; Foubelo, F.; Ferrández, J. V. Tetrahedron
2003, 59, 2083.
(82), 91 (10).
HRMS (EI): m/z calcd for C19H28O (M): 272.2140; found:
272.2132.
Acknowledgement
This work was financially supported by the DGES from the Spanish
Ministerio de Educación Cultura y Deporte (project no. PB-97-
0133) and by the Generalitat Valenciana (project no. GV01-443).
B.M. thanks the Spanish Ministerio de Ciencia y Tecnología for a
predoctoral fellowship.
References
(1) For reviews, see: (a) Nájera, C.; Yus, M. Trends Org. Chem.
1991, 2, 155. (b) Nájera, C.; Yus, M. Recent Res. Dev. Org.
Chem. 1997, 1, 67. (c) Nájera, C.; Yus, M. Curr. Org.
Chem. 2003, 7, 867.
(2) (a) Wakefield, B. Organolithium Methods; Academic Press:
London, 1988. (b) Clayden, J. Organolithiums: Selectivity
for Synthesis; Pergamon: Amsterdam, 2002.
(3) For reviews, see: (a) Yus, M.; Foubelo, F. Rev. Heteroatom
Chem. 1997, 17, 73. (b) Yus, M.; Foubelo, F. Targets in
Heterocyclic Systems 2002, 6, 136. (c) Yus, M. Pure Appl.
Chem. 2003, 75, 1453.
(8) For the first account of this reaction, see: Yus, M.; Ramón,
D. J. J. Chem. Soc., Chem. Commun. 1991, 398.
(9) For reviews, see: (a) Yus, M. Chem. Soc. Rev. 1996, 155.
(b) Ramón, D. J.; Yus, M. Eur. J. Org. Chem. 2000, 225.
(c) Yus, M. Synlett 2001, 1197.
(10) (a) Gómez, C.; Ruiz, S.; Yus, M. Tetrahedron Lett. 1998, 39,
1397. (b) Gómez, C.; Ruiz, S.; Yus, M. Tetrahedron 1999,
55, 7017.
(4) (a) Alonso, F.; Lorenzo, E.; Yus, M. Tetrahedron Lett. 1997,
38, 2187. (b) Sabes, S. F.; Urbanek, R. A.; Forsyth, C. J. J.
Am. Chem. Soc. 1998, 120, 2534. (c) Alonso, F.; Lorenzo,
E.; Yus, M. Tetrahedron Lett. 1998, 39, 3303. (d) Lorenzo,
E.; Alonso, F.; Yus, M. Tetrahedron 2000, 56, 1745.
(e) Lorenzo, E.; Alonso, F.; Yus, M. Tetrahedron Lett. 2000,
41, 1661. (f) Alonso, F.; Falvello, L. R.; Fanwick, P. E.;
Lorenzo, E.; Yus, M. Synthesis 2000, 949. (g) Alonso, F.;
Meléndez, J.; Yus, M. Helv. Chim. Acta 2002, 85, 3262.
(h) Yus, M.; Maciá, B.; Gómez, C. Tetrahedron 2003, 59,
5183. (i) Alonso, F.; Lorenzo, E.; Meléndez, J.; Yus, M.
Tetrahedron 2003, 59, 5199.
(5) (a) Azzena, U.; Demartis, S.; Fiori, M. G.; Melloni, G.;
Pisano, L. Tetrahedron Lett. 1995, 36, 5641. (b)Almena, J.;
Foubelo, F.; Yus, M. J. Org. Chem. 1996, 61, 1859.
(c) Almena, J.; Foubelo, F.; Yus, M. Tetrahedron 1996, 52,
8545. (d) For a review, see:Azzena, U. Trends Org. Chem.
1997, 6, 55. (e) Almena, J.; Foubelo, F.; Yus, M.
(11) Yus, M.; Gómez, C.; Candela, P. Tetrahedron 2002, 58,
6207.
(12) For studies on the mechanism of this reaction, see: (a) Yus,
M.; Herrera, R. P.; Guijarro, A. Tetrahedron Lett. 2001, 42,
3455. (b) Yus, M.; Herrera, R. P.; Guijarro, A. Chem.–Eur.
J. 2002, 8, 2574. (c) Herrera, R. P.; Guijarro, A.; Yus, M.
Tetrahedron Lett. 2003, 44, 1309. (d) Herrera, R. P.;
Guijarro, A.; Yus, M. Tetrahedron Lett. 2003, 44, 1313.
(13) Almena, J.; Foubelo, F.; Yus, M. Tetrahedron 1995, 51,
3351.
(14) Almena, J.; Foubelo, F.; Yus, M. Tetrahedron 1995, 51,
3365.
(15) (a) Soler, T.; Bachki, A.; Falvello, L. R.; Foubelo, F.; Yus,
M. Tetrahedron: Asymmetry 1998, 9, 3939. (b) Soler, T.;
Bachki, A.; Falvello, L. R.; Foubelo, F.; Yus, M.
Tetrahedron: Asymmetry 2000, 11, 493.
(16) (a) Falvello, L. R.; Foubelo, F.; Soler, T.; Yus, M.
Tetrahedron: Asymmetry 2000, 11, 2063. (b) Foubelo, F.;
Soler, T.; Yus, M. Tetrahedron: Asymmetry 2001, 12, 801.
(17) Yus, M.; Gomis, J. Eur. J. Org. Chem. 2003, 2043.
(18) Pastor, I. M.; Yus, M. Tetrahedron Lett. 2000, 41, 1589.
(19) Pastor, I. M.; Yus, M. Tetrahedron 2001, 57, 2371.
(20) Yus, M.; Gomis, J. Tetrahedron Lett. 2001, 42, 5721.
(21) Yus, M.; Gomis, J. Eur. J. Org. Chem. 2002, 1989.
(22) Yus, M.; Gomis, J. Tetrahedron 2003, 59, 4967.
Tetrahedron 1997, 53, 5563. (f) Azzena, U.; Carta, S.;
Melloni, G.; Sechi, A. Tetrahedron 1997, 53, 16205.
(6) (a) Maercker, A. Angew. Chem., Int. Ed. Engl. 1987, 26,
972. (b) Lazana, M. C. R. L. R.; Franco, M. L. T. M. B.;
Herold, B. J. J. Am. Chem. Soc. 1989, 111, 8640.
(c) Casado, F.; Pisano, L.; Farriol, M.; Gallardo, I.; Marquet,
J.; Melloni, G. J. Org. Chem. 2000, 65, 322. (d) Azzena,
U.; Denurra, T.; Melloni, G.; Piroddi, A. M. J. Org. Chem.
1990, 55, 5386. (e) Azzena, U.; Denurra, T.; Melloni, G.;
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