Fluoride-Promoted Rearrangement of Organo Silicon Compounds: A New Synthesis of 2-(Arylmethyl)aldehydes from 1-Alkynes

Article abstract of DOI:10.1021/jo0351062

A new approach to 2-(arylmethyl)aldehydes 4 based upon a 1,2-anionotropic rearrangement of an aryl group is presented. The synthetic sequence begins with a silylformylation reaction of terminal acetylenes 5 with aryl and heteroaryl silanes 6, followed by treatment of the products (Z)-1 with TBAF. The optimization of the experimental conditions of the fluoride-promoted step is described, together with the synthetic potentialities of the process. A plausible mechanism of the rearrangement reaction is reported that suggests the addition of the fluoride ion to the arylsilicon moiety of β-silylalkenals (Z)-1 and the consequent migration of the aryl group to the adjacent carbon atom. Both aryl and heteroaryl substituents can rearrange without any loss of configuration. Bromofunctionalized substrates undergo an intramolecular reaction that affords exclusively carbacyclobenzyl aldehydes, further enhancing the high synthetic value of this method.

Full text of DOI:10.1021/jo0351062

F lu or id e-P r om oted Rea r r a n gem en t of Or ga n o Silicon Com p ou n d s:
A New Syn th esis of 2-(Ar ylm eth yl)a ld eh yd es fr om 1-Alk yn es
Laura Antonella Aronica, Patrizio Raffa, Anna Maria Caporusso, and Piero Salvadori*
Dipartimento di Chimica e Chimica Industriale, Universita` degli Studi di Pisa,
Via Risorgimento 35, 56126 Pisa, Italy
psalva@dcci.unipi.it
Received J uly 29, 2003
A new approach to 2-(arylmethyl)aldehydes 4 based upon a 1,2-anionotropic rearrangement of an
aryl group is presented. The synthetic sequence begins with a silylformylation reaction of terminal
acetylenes 5 with aryl and heteroaryl silanes 6, followed by treatment of the products (Z)-1 with
TBAF. The optimization of the experimental conditions of the fluoride-promoted step is described,
together with the synthetic potentialities of the process. A plausible mechanism of the rearrangement
reaction is reported that suggests the addition of the fluoride ion to the arylsilicon moiety of
â-silylalkenals (Z)-1 and the consequent migration of the aryl group to the adjacent carbon atom.
Both aryl and heteroaryl substituents can rearrange without any loss of configuration. Bromo-
functionalized substrates undergo an intramolecular reaction that affords exclusively carbacy-
clobenzyl aldehydes, further enhancing the high synthetic value of this method.
In tr od u ction
ineffective, and the reaction with BF3-acetic acid com-
plex generated a mixture of (E)-2-(dimethylphenylsilyl-
methylene)hexanal (E)-1a a and 2-benzylhexanal 4a a .
Complete isomerization of (Z)-1a a to (E)-1a a resulted
when paratoluensulfinic acid was used.
Silicon has received the attention of chemists for many
years because of its low cost, abundance, and nontoxic
properties. In particular, the use of organosilicon com-
pounds to synthetic laboratory and large-scale applica-
tions has been growing intensively, due to their relatively
high stability and their ability to induce chemo-, regio-,
and stereoselective transformation when combined with
appropriate catalysts. For instance, the transition-metal-
mediated hydrosilylation1 and, more recently, the rhodium-
mediated silylformylation reactions2 are among the suit-
able methods used to functionalize carbon-carbon multiple
bonds.
During our studies on the silylformylation of terminal
acetylenes3 with dimethylphenylsilane, we investigated
the synthetic potentialities of (Z)-2-(dimethylphenylsi-
lylmethylene)hexanal (Z)-1a a . While the isomerization,
the reduction, and the Wittig transformation of this
compound can be easily performed,3,4 all the attempts to
achieve the protodesilylation reaction surprisingly failed5
(Scheme 1). KF/MeOH and TBAF/MeOH were completely
On the other hand, we observed that when (Z)-2-
(dimethylphenylsilylmethylene)hexanal (Z)-1a a was re-
acted with a fluoride source such as tetrabutylammonium
fluoride (TBAF) in a polar aprotic solvent5 (THF, DMSO,
CH3CN) 2-benzylhexanal 4a a was exclusively formed
(Scheme 1). This appeared very promising from the
synthetic point of view. The reaction seemed to involve
an anionotropic 1,2-migration of a phenyl group from the
silicon atom to the adjacent carbon atom of the R,â-
unsaturated aldehyde (Z)-1a a . To our knowledge, only
Fleming6 described a similar phenyl transposition from
Si to the â position of a polysilylated enone system. As a
matter of fact, while silicon migrations from carbon to
oxygen (Brook rearrangements) are well-known pro-
cesses,7 the shift of a carbon (especially aryl groups) from
silicon to an adjacent carbon atom is more recent and
usually occurs in acylsilanes8 and in molecules character-
* Corresponding author.
(1) Marciniec, B. Silicon Chem. 2002, 1, 155-175 and references
therein.
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1994, 13, 1081-1088. (e) Zhou, J .; Alper, H. Organometallics 1994,
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10.1021/jo0351062 CCC: $25.00 © 2003 American Chemical Society
Published on Web 10/28/2003
9292
J . Org. Chem. 2003, 68, 9292-9298

Synthesis of 2-(Arylmethyl)aldehydes from 1-Alkynes
SCHEME 1
ized by the presence of a good leaving group such as
halide and triflate.9
The â-silylalkenals (Z)-1 were then prepared by silyl-
formylation2 of equimolar amounts of the corresponding
acetylenes 5 and the appropriate aryldimethylsilane 6,
as reported in Table 1. The reactions were performed at
room temperature, in a stainless steel autoclave, and
required a catalytic (0.1mol %) amount of Rh4(CO)12 with
respect to the silane.
Here, we report the optimization and the extension of
this fluoride mediated reaction to several â-silylalkenals
(Z)-1, which can represent a novel route to the prepara-
tion of a large variety of 2-arylmethyl and 2-heteroaryl-
methyl aldehydes from 1-alkynes, usually obtained
through complex synthetic pathways.10
Both aromatic and heteroaromatic silanes 6a -f were
successfully reacted, affording the silylformylation prod-
ucts (Z)-1 with good yields and complete regio- and
stereoselectivity. As we previously reported,3 the silyl-
formylation process was markedly affected by the struc-
ture of the reagents: linear â-silylalkenals (Z)-1a a and
(Z)-1fa were obtained with excellent yields under mild
experimental conditions (10 atm of CO, Table 1, entries
1 and 11), while higher CO pressure (25-50 atm) and
longer reaction times were required when the steric
hindrance of both the alkynes and the hydrosilanes
increased (Table 1, entries 2-5 and 8).
To optimize the reaction of fluoride-mediated rear-
rangement, preliminary experiments were performed
using (Z)-2-(dimethylphenylsilylmethylene)hexanal (Z)-
1a a as model compound (Table 2). All the reactions were
carried out in tetrahydrofuran since a polar aprotic
solvent was necessary to achieve the fluoride ion coor-
dination to the silicon atom of the â-silylalkenal.5 Indeed,
in the presence of a polar protic solvent such as methanol,
no reaction occurred, probably due to the strong hydrogen
bonds between MeO-H and F- that could generate a
shield effect around the fluoride ion. On the other hand,
when a solution of (Z)-1a a in THF was treated with an
equimolar amount of TBAF at room temperature, the
complete consumption of the â-silylalkenal and the
formation of the corresponding 2-benzylhexanal 4a a was
observed immediately after the addition of tetrabutyl-
ammonium fluoride (1 M in THF) to (Z)-1a a and hydro-
lyzation with water. According to this method (A, Table
2, entry 1), the desired product 4a a was obtained with
good but not excellent yield after purification on silica
gel column. The lack of purified product (60% yield vs
100% conversion) could be possibly ascribed to the mild
acid experimental conditions that could favor the forma-
tion of high weighted polycondensated products, detected
by GC analysis. With the aim of minimizing the extent
of byproducts, hydrolysis with a pH 7 buffer (KH2PO4/
Resu lts a n d Discu ssion
Alkynes 5a -f and arylsilanes 6a -f (Table 1) were
chosen as precursors for the synthesis of the â-silylal-
kenals (Z)-1, having different steric and electronic fea-
tures.
Except for the commercially available 1-hexyne (5a )
and bromoalkynes 5e,f, acetylenes 5b-d were prepared
from the corresponding bromoallenes through a well-
known procedure.11 The synthesis of arylsilanes was
performed by reacting excess Me2ClSiH with ArMgBr,
according to the method described by Hiyama and co-
workers12 (Scheme 2). Both aromatic and heteroaromatic
silanes were obtained with good to excellent yields (61-
85%).
(9) (a) Damrauer, R.; Yost, V. E.; Danahey, S. E.; O’Connell, B. K.
Organometallics 1985, 4, 1779-1784. (b) Hudrlik, P. F.; Abdallah, Y.
M.; Kulkarni, A. K.; Hudrlik, A. M. J . Org. Chem. 1992, 57, 6552-
6556. (c) Allen, J . M.; Aprahamian, S. L.; Sans, E. A.; Shechter, H. J .
Org. Chem. 2002, 67, 3561-3574.
(10) (a) Myers, A. G.; Yang, B. H.; Chen, H.; Gleason, J . L. J . Am.
Chem. Soc. 1994, 116, 9361-9362. (b) Tanner, D.; Birgersson, C.;
Gogoll, A. Tetrahedron 1994, 50, 9797-9824. (c) Myers, A. G.; Yang,
B. H.; Chen, H.; McKinstry, L.; Kopecky, D. J .; Gleason, J . L. J . Am.
Chem. Soc. 1997, 119, 6496-6511. (d) Barluenga, J . J . Pure Appl.
Chem. 1999, 71, 1385-1391. (e) Bull, S. D.; Davies, S. G.; Nocholson,
R. L.; Sanganee, H. J .; Smith, A. D. Tetrahedron: Asymmetry 2000,
11, 3475-3479. (f) Bremand, N.; Mangeney, P.; Normant, J . F. Synlett
2000, 4, 532-534. (g) Bremand, N.; Mangeney, P.; Normant, J . F.
Tetrahedron Lett. 2001, 42, 1883-1885.
(11) (a) Crandall, J . K.; Keiton, D. J .; Kohone, J .J . Org. Chem. 1968,
33, 3655-3657. (b) Bernadou, F.; Mesnard, D.; Miginiac, L. J . Chem.
Res., Synop. 1978, 106-107. (c) Caporusso, A. M.; Zoppi, A.; Da
Settimo, F.; Lardicci, L. Gazz. Chim. Ital. 1985, 115, 293-295. (d)
Caporusso, A. M.; Rosini, C.; Lardicci, L.; Polizzi, C.; Salvadori, P. Gazz.
Chim. Ital. 1986, 116, 467-469. (e) Caporusso, A. M.; Polizzi, C.;
Lardicci, L. Tetrahedron Lett. 1987, 28, 6073-6076. (f) Caporusso, A.
M.; Polizzi, C.; Lardicci, L. J . Org. Chem. 1987, 52, 3920-3923. (g)
Polizzi, C.; Consoloni, C.; Lardicci, L.; Caporusso, A. M. J . Organomet.
Chem. 1991, 417, 289-304.
(12) Fujita, M.; Hiyama, T. J . Org. Chem. 1988, 53, 5405-5415.
J . Org. Chem, Vol. 68, No. 24, 2003 9293

Aronica et al.
TABLE 1. Silylfor m yla tion of 1-Alk yn es 5a
a
Reaction performed in a stainless steel autoclave, with 3 mmol of silane 6 and 3 mmol of 1-alkyne 5, in 3 mL of toluene, at room
temperature. Yields of purified products. c Reaction time: 48 h.
b
SCHEME 2
up the formation of aldehyde 4 (Scheme 3). Indeed, the
proposed mechanism involves the addition of fluoride to
silicon yielding a pentacoordinate Si atom 7, aryl-1,2-
anionotropic rearrangement to the adjacent carbon atom
with formation of enolate 8, and its possible cyclization
and final removal of enol silyl ether 10 by water or excess
fluoride itself (Scheme 3).
NaOH) was carried out. Yet, no increase of the product
amount was observed, even operating at low temperature
(methods B and C, Table 2). A remarkable improvement
of the yield (78%) was achieved by performing a reverse
addition of the â-silylalkenal to a solution of excess TBAF
in THF (method E). The same result was obtained when
this methodology was extended to different â-silylalde-
hydes such as o-tolyl-, p-tolyl-, and even thienyldimeth-
ylsilylalkenal, confirming the large applicability and the
high synthetic potentialities of the rearrangement pro-
cess.
While all attempts to isolate enol silyl ethers 9 and 10
were unsuccessful, the presence of enolate 8 as interme-
diate of the reaction was confirmed by the results
obtained performing the reaction with the bromo-
substituted aldehydes (Z)-1ea and (Z)-1fa (Scheme 4).
Surprisingly, not only the cyclopentyl but even the
cyclopropyl derivatives were easily formed, indicating an
intramolecular nucleophilic attack of the carbanion to the
Br-CH2 bond. The cyclization process was so favored
(82-90% yields of the purified product) that the experi-
mental conditions did not need to be optimized in these
cases.
In all cases, the yields of the corresponding 3-arylal-
dehydes 4 were clearly enhanced (Table 2, entries 5, 7,
9, and 13 vs entries 1, 6, 8, and 12). The excess
tetrabutylammonium solution, which contains 5% water,
probably favors the fast hydrolysis of enol silyl ethers 9
and 10, reasonably formed during the process, speeding
The described results demonstrate that no protodesi-
lylation process may occur when a â-silylalkenal is
treated with a fluoride source that is under the common
9294 J . Org. Chem., Vol. 68, No. 24, 2003

Synthesis of 2-(Arylmethyl)aldehydes from 1-Alkynes
TABLE 2. TBAF -In d u ced An ion otr op ic Rea r r a n gem en t of â-Silyla lk en a l
a
b
Yields of purified products. Method A: 1 mL of TBAF (1 M in THF) was added to 1 mmol of aldehyde in 10 mL of THF at room
temperature and then hydrolyzed immediately with water. c Method B: 1 mL of TBAF (1 M in THF) was added to 1 mmol of aldehyde
d
in 10 mL of THF at room temperature and then hydrolyzed immediately with KH2PO4-NaOH (pH 7). Method C: 1 mL of TBAF (1 M
in THF) was added to 1 mmol of aldehyde in 10 mL of THF at 0 °C and then hydrolyzed immediately with KH2PO4-NaOH (pH 7).
e Method D: 1 mmol of aldehyde was added to 1 mL of TBAF (1 M in THF) dissolved in 10 mL at room temperature and then hydrolyzed
f
immediately with water. Method E: 1 mmol of aldehyde was added to 2.5 mL of TBAF (1 M in THF) dissolved in 10 mL at room temperature
and then hydrolyzed immediately with water. Reactions performed in DMSO. A diastereoisomeric (50:50) mixture was obtained.
g
h
protodesilylation conditions.13 On the other hand, the
transformation of the â-silylalkenals into the correspond-
ing R,â-unsaturated aldehydes would represent an al-
ternative preparation of these important molecules with
respect to the direct hydroformylation of alkynes, which
usually suffers from a lack of regio-, chemo-, and stereo-
selectivity.14 On the contrary, an easy three-step sequence
of reduction,15 protodesilylation,16 and reoxidation17 can
afford the desired aldehydes, as described in Scheme 5
for (Z)-2-(dimethylphenylsilylmethylene)hexanal (Z)-1a a .
(13) (a) Bachi, M. D.; Bosch, E. Tetrahedron Lett. 1988, 29, 2581-
2584. (b) J efford, C. W.; Moulin, M. Helv. Chim. Acta 1991, 74, 336-
342. (c) Kishi, N.; Maeda, T.; Mikami, K.; Nakai, T. Tetrahedron 1992,
48, 4087-4098. (d) Brasseur, D.; Marek, I.; Normant, J . F. Tetrahedron
1996, 52, 7235-7250. (e) Chenede´, A.; Abd. Rahamn, N.; Fleming, I.
Tetrahedron Lett. 1997, 38, 2381-2382. (f) Shepard, M. S.; Carreira,
E. M. J . Am. Chem. Soc. 1997, 119, 2596-2605. (g) Anderson, J . C.;
Flaherty, A. J . Chem. Soc., Perkin Trans. 1 2000, 3025-3027.
(14) (a) Fell, B.; Beutler, M. Tetrahedron Lett. 1972, 13, 3455-3456.
(b) Botteghi, C.; Salomon, C. Tetrahedron Lett. 1974, 15, 4285-4288.
(c) J ohnson, J . R.; Cuny, G. D.; Buchwald, S. L. Angew. Chem., Int.
Ed. Engl. 1995, 34, 1760-1761. (d) Ishii, Y.; Miyashita, K.; Kamita,
K.; Hidai, M. J . Am. Chem. Soc. 1997, 119, 6448-6449.
J . Org. Chem, Vol. 68, No. 24, 2003 9295

Aronica et al.
SCHEME 3
SCHEME 4
aptitudes of the aryl and heteroaryl moiety appeared to
be greater than that of methyl. Considering that the
anionotropic migration can be successfully extended to
a large variety of â-silylalkenal characterized by different
steric and electronic features, the method can easily
afford 2-(arylmethyl)aldehydes and related derivatives,
useful building blocks for organic synthesis18 and impor-
tant industrial substrates.19 It is noteworthy that when
the reaction was performed with a bromo-functionalized
â-silylalkenal an unexpected intramolecular process oc-
curred and carbacyclobenzyl aldehydes were obtained
with excellent yields.
Exp er im en ta l Section
SCHEME 5
Gen er a l Rem a r k s. All solvents were reagent-grade ma-
terials purified by standard methods. Tetrahydrofuran and
toluene were distilled from sodium immediately before use.
Dimethylphenylsilane and 1-hexyne were distilled and stored
over molecular sieves. Bromoalkynes 5e,f were used without
20
purification. Rh4(CO)12 was prepared and purified as previ-
ously reported. 3-Methyl-1-butyne 5b, 3-methyl-1-pentyne 5c,
and 3-phenyl-1-butyne 5d were synthesized from the corre-
sponding bromoallenes according to literature methods.11 (o-
Methylphenyl)dimethylsilane21 6b, (p-methylphenyl)dimeth-
ylsilane12 6c, (p-methoxyphenyl)dimethylsilane12 6d , biphenyl-
4-yl-dimethylsilane22 6e, and dimethylthiophen-2-ylsilane23 6f
were generated from the corresponding Grignard reagents
according to the method described by Hiyama and co-work-
ers.12
GLC analyses were performed with a DB1 capillary column
(30 m × 0.52 mm, 5 micron) using He as the carrier gas and
a flame ionization detector (FID). Column chromatography was
performed on silica gel 60 (230-400 mesh).
The three reactions were performed under mild experi-
mental conditions, and the crude products were employed
in the next step without any further purification, afford-
ing aldehyde 12a a with a 90% total yield from (Z)-1a a .
The protodesilylation process of the allylic alcohol (Z)-
2a a was easily performed, since the presence of the OH
in the â position to the silyl moiety promotes the removal
of the silicon group (beta effect).14,6 The subsequent
oxidation17 with pyridinium dichromate (PDC) yielded
the desired unsaturated aldehyde 12a a quantitatively.
Gen er a l P r oced u r e for th e Rh od iu m -Ca ta lyzed Silyl-
for m yla tion of 1-Alk yn es 5a -f w ith sila n es 6a -f. Carbo-
nylation reactions were run in
a 25 mL stainless steel
autoclave fitted with a Teflon inner crucible and a stirring bar.
In a typical run, 3 mmol of silane, 3 mmol of the required
Con clu sion s
(18) (a) Sola`, L.; Reddy, K. S.; Vidal-Ferran, A.; Moyano, A.; Pericas,
M. A.; Riera, A.; Alvarez-Larena, A.; Pinella, J . F. J . Org. Chem. 1998,
63, 7078-7082. (b) Yang, H. W.; Romo, D. Tetrahedron Lett. 1998, 39,
2877-2880. (c) Roda, G.; Riva, G.; Danieli, B. Tetrahedron: Asymmetry
1999, 10, 3939-3949. (d) Boucley, C.; Cahiez, G.; Carini, S.; Cere`, V.;
Comes-Franchini, M.; Knochel, P.; Pollicino, S.; Ricci. A. J . Organomet.
Chem. 2001, 624, 223-228.
(19) (a) Rhone-Poulenc DE, 1145161, 1963; Chem. Abstr. 1963, 59,
9900d. (b) Soda Aromatic Co. NL, 6502482, 1964; Chem. Abstr. 1966,
64, 19497g. (c) Givaudan, L.; Cie DE, 2851024, 1979; Chem. Abstr.
1979, 91, 107808a.
(20) Martinengo, S.; Giordano, G.; Chini, P. Inorg. Synth. 1990, 28,
242-245.
(21) Hevesi, L.; Dehon, M.; Crutzen, R.; Lazarescu-Grigore, A. J .
Org. Chem. 1997, 62, 2011-2017.
(22) Ospita, J .; Sugimoto, K.; Watanabe, T.; Kunai, A.; Ishikawa,
M.; Aoyama, S. J . Organomet. Chem 1998, 564, 47-56.
(23) Hu, S. S.; Weber, W. P. J . Organomet. Chem 1989, 369, 155-
163.
This paper describes a new synthetic pathway to
2-(arylmethyl)aldehydes from terminal acetylenes con-
sisting of a two-step silylformylation-aryl migration
sequence. The aryl anionotropic rearrangement, which
represents the key step of the method, was optimized.
During the rearrangement process, the original config-
uration of the Ar group on the silicon atom (o-tolyl,
p-tolyl, 1-thienyl, ...) was maintained and the migratory
(15) Eguchi, M.; Zeng, Q.; Korda, A.; Ojima, I. Tetrahedron Lett.
1993, 915-918.
(16) Oda, H.; Sato, M.; Morizawa, Y.; Oshima, K.; Nozaki, H.
Tetrahedron 1985, 41, 3257-3268.
(17) Shimizu, N.; Imazu, S.; Shibata, F.; Tsuno, Y. Bull. Chem. Soc.
J pn. 1991, 64, 1122-1128.
9296 J . Org. Chem., Vol. 68, No. 24, 2003

Synthesis of 2-(Arylmethyl)aldehydes from 1-Alkynes
1-alkyne, 3 mL of toluene, and a 0.1 mmol % of Rh4(CO)12 were
put, under CO atmosphere, in a Pyrex Schlenk tube. This
solution was introduced in the autoclave, previously placed
under vacuum (0.1 mmHg), by a steel siphon. The reactor was
pressurized with carbon monoxide and the mixture was stirred
at room temperature for 24 h, unless otherwise specified. After
removal of excess CO (fume hood), the reaction mixture was
diluted with pentane, filtered (Celite), and concentrated by
bulb-to-bulb distillation (1 mmHg). The residue was purified
by column chromatography on silica gel using pentane/EtOAc
(95/5) as eluent, affording the pure aldehydes (Z)-1a a -fa
(Table 1).
6H), 2.78 (t, J ) 7.6 Hz, 2H), 3.25 (t, J ) 7.6 Hz, 2H), 6.96 (s,
1H), 7.34-7.43 (m, 3H), 7.49-7.56 (m, 2H), 9.41 (s, 1H); 13C
NMR (50.3 MHz, CDCl3) δ -1.7, 30.0, 32.0, 128.2, 129.7, 133.7,
136.3, 153.4, 154.8, 194.8; GC-MS (EI) m/z (rel int) 297 (M+),
295 (M+), 283 (8), 281 (12), 203 (62), 210 (8), 189 (81), 141 (86),
135 (100), 129 (66), 105 (46), 91 (28), 77 (55). Anal. Calcd for
C
13H17BrOSi: C, 52.53; H, 5.76; Br, 26.88. Found: C, 52.51;
H, 5.73; Br, 26.85.
6-B r o m o -2-[(d im e t h y lp h e n y ls ily l)m e t h y le n e ]h e x -
a n a l (Z)-1fa : colorless oil; IR (neat) 3063, 2957, 2736, 1686,
1589, 1455, 1428, 1251 cm-1 1H NMR (200 MHz, CDCl3) δ
;
0.51 (s, 6H), 1.50-1.68 (m, 2H), 1.78-1.94 (m, 2H), 2.32 (t, J
) 8.1 Hz, 2H), 3.39 (t, J ) 6.6 Hz, 2H), 6.96 (s, 1H), 7.33-
7.43 (m, 3H), 7.45-7.55 (m, 2H), 9.76 (s, 1H); 13C NMR (50.3
MHz, CDCl3) δ -0.1, 26.9, 30.9, 32.3, 33.3, 128.2, 129.5, 133.5,
137.8, 149.6, 156.2, 193.0; GC-MS (EI) m/z (rel int) 311 (M+
- 15), 309 (M+ - 15), 249, (15), 247 (16), 203 (43), 187 (97),
167 (28), 139 (64), 129 (100), 105 (64), 91 (81), 75 (50), 43 (58).
Anal. Calcd for C15H21BrOSi: C, 55.38; H, 6.51; Br, 24.56.
Found: C, 55.34; H, 6.53; Br, 24.59.
Spectral data of (Z)-1a a , (Z)-1ba , (Z)-1ca , and (Z)-1d a
perfectly agreed with literature.3
2-[(Dim et h yl-o-t olylsilyl)m et h ylen e]h exa n a l (Z)-1a b :
colorless oil; IR (neat) 3048, 2952, 2741, 1683, 1589, 1448, 1252
1
cm-1; H NMR (200 MHz, CDCl3) δ 0.52 (s, 6H), 0.89 (t, J )
7.2 Hz, 3H), 0.24-1.42 (m, 4H), 2.27 (dt, J ) 7.3, 0.9 Hz, 2H),
2.36 (s, 3H), 6.98 (t, J ) 0.9 Hz, 1H), 7.24-7.44 (m. 3H), 7.57
(dd, J ) 7.3, 1.5 Hz, 1H), 9.97 (s, 1H); 13C NMR (50.3 MHz,
CDCl3) δ 0.4, 13.9, 22.4, 23.3, 30.6, 31.4, 125.3, 129.9, 130.1,
134.1, 136.4, 143.2, 150.2, 156.6, 193.3; GC-MS (EI) m/z (rel
int) 245 (M+ - 15), 203 (35), 169 (15), 151(18), 140 (20), 127
Gen er a l P r oced u r es for th e TBAF -P r om oted Rea r -
r a n gem en ts of (Z)-1: Meth od A. To a solution of 1 mmol of
(Z)-1 in 10 mL of THF was added, at room temperature, 1
mL of TBAF (1 M in THF). The reaction mixture was
hydrolyzed with water and extracted with Et2O, and the
organic layers were dried over Na2SO4. After concentration
under vacuum, the crude product was purified by column
chromatography on silica gel using hexane/EtOAc (90/10) as
eluent. Meth od B. To a solution of 1 mmol of (Z)-1 in 10 mL
of THF was added, at room temperature, 1 mL of TBAF (1 M
in THF). The reaction mixture was hydrolyzed with KH2PO4-
NaOH (pH 7) and submitted to the usual workup (method A).
Meth od C. Identical to method B, except for the experimental
temperature (0 °C). Meth od D. One millimole of aldehyde was
added to 1 mL of TBAF (1 M in THF) dissolved in 10 mL of
THF, at room temperature, hydrolyzed immediately after with
water, and extracted with Et2O, and the organic layers were
dried over Na2SO4. After concentration under vacuum, the
crude product was purified by column chromatography on
silica gel using hexane/EtOAc (90/10) as eluent. Meth od E.
Identical to method D, except for the quantity of TBAF (2.5
mL).
(33), 91 (12), 75 (35), 61 (33), 43 (100). Anal. Calcd for C16H24
OSi: C, 73.79; H, 9.29. Found: C, 73.73; H, 9.26.
-
2-[(Dim eth yl-p-tolylsilyl)m eth ylen e]h exa n a l (Z)-1a c:
colorless oil; IR (neat) 3052, 2941, 2733, 1684, 1590, 1458,
1
1250, 1106 cm-1; H NMR (200 MHz, CDCl3) δ 0.53 (s, 6H),
0.95 (t, J ) 6.9 Hz, 3H), 1.32-1.52 (m, 4H), 2.35 (t, J ) 7.8
Hz, 2H), 2.38 (s, 3H), 6.97 (s, 1H), 7.22 (d, J ) 7.5 Hz, 2H),
7.46 (d, J ) 7.5 Hz, 2H), 9.82 (s, 1H); 13C NMR (50.3 MHz,
CDCl3) δ 0.02, 13.9, 21.5, 22.5, 30.7, 31.6, 129.0, 133.6, 134.4,
139.4, 149.2, 157.1, 193.3; GC-MS (EI) m/z (rel int) 245 (M+-
15), 217 (11), 203 (70), 149(32), 127 (38), 119 (15), 105 (16), 91
(15), 75 (25), 61 (34), 43 (100). Anal. Calcd for C16H24OSi: C,
73.79; H, 9.29. Found: C, 73.76; H, 9.29.
2-[(4-Me t h oxyp h e n yl)d im e t h ylsilylm e t h yle n e ]h e x-
a n a l (Z)-1a d : colorless oil; IR (neat) 3009, 2956, 2847, 2737,
1682, 1594, 1503, 1464, 1279, 1249, 1112 cm-1; 1H NMR (200
MHz, CDCl3) δ 0.48 (s, 6H), 0.90 (t, J ) 7.3 Hz, 3H), 1.26-
1.44 (m, 4H), 2.29 (t, J ) 7.2 Hz, 2H), 3.80 (s, 3H), 6.89-6.93
(m, 3H), 7.43 (d, J ) 8.4 Hz, 2H), 9.77 (s, 1H); 13C NMR (50.3
MHz, CDCl3) δ 0.1, 13.9, 22.4, 30.6, 31.5, 55.0, 114.0, 128.8,
135.0, 149.4, 157.0, 160.7, 193.4; GC-MS (EI) m/z (rel int) 276
(M+), 161 (42), 219 (100), 165 (40), 159 (43), 135 (21), 127 (50),
91 (24), 75 (43), 59 (66). Anal. Calcd for C16H24O2Si: C, 69.51;
H, 8.75. Found: C, 69.48; H, 8.72.
2-Ben zylh exa n a l 4a a perfectly agreed with the literature.4
2-(2-Meth ylben zyl)h exa n a l, 4a b: colorless oil; IR (neat)
2956, 2930, 2716, 1726, 1464 cm-1; 1H NMR (200 MHz, CDCl3)
δ 0.88 (t, J ) 6.6 Hz, 3H), 1.20-1.38 (m, 2H), 1.40-1.78 (m,
4H); 2.31 (s, 3H), 2.52-2.6 (m, 1H), 2.69 (dd, J ) 6.6, 13.3 Hz,
1H), 2.97 (dd, J ) 6.6, 13.3 Hz, 1H), 7.10-7.14 (m, 4H), 9.53
(d, J ) 2.6, 1H); 13C NMR (50.3 MHz, CDCl3) δ 13.8, 19.4, 22.7,
28.7, 29.1, 32.4, 52.1, 125.9, 126.4, 126.5, 130.4, 136.0, 137.1,
204.6; GC-MS (EI) m/z (rel int) 147 (M+-57), 129 (21), 105
(100), 91 (18), 77 (10). Anal. Calcd for C14H20O: C, 82.30; H,
9.87. Found: C, 82.28; H, 9.91.
2-(4-Meth ylben zyl)h exa n a l, 4a c: colorless oil; IR (neat)
2956, 2932, 2712, 1725, 1513, 1248 cm-1; 1H NMR (200 MHz,
CDCl3) δ 0.87 (t, J ) 6.6 Hz, 3H), 1.23-1.35 (m, 2H), 1.42-
1.53 (m, 2H), 1.58-1.70 (m, 2H), 2.31 (s, 3H), 2.52-2.64 (m,
1H), 2.67 (dd, J ) 6.6, 13.6 Hz, 1H), 2.94 (dd, J ) 6.6, 13.6
Hz, 1H), 7.04 (d, J ) 8.4 Hz, 2H), 7.09 (d, J ) 8.4 Hz, 2H)
9.64 (d, J ) 2.4, 1H); 13C NMR (50.3 MHz, CDCl3) δ 13.8, 20.9,
22.7, 28.2, 29.0, 34.6, 53.4, 128.8, 129.1, 135.7, 135.8, 204.8;
GC-MS (EI) m/z (rel int) 204 (M+), 147 (30), 91(17), 77 (12).
Anal. Calcd for C14H20O: C, 82.30; H, 9.87. Found: C, 82.28;
H, 9.85.
2-[(Bip h en yl-4-yld im eth ylsila n yl)m eth ylen e]h exa n a l
(Z)-1a e: colorless oil; IR (neat) 3066, 3026, 2957, 2738, 1682,
1
1597, 1428, 1254 cm-1; H NMR (200 MHz, CDCl3) δ 0.57 (s,
6H), 0.95 (t, J ) 6.9 Hz, 3H), 1.28-1.56 (m, 4H), 2.37 (t, J )
7.0 Hz, 2H), 6.99 (s,1H), 7.35-7.50 (m. 4H), 7.60-7.65 (m, 5H),
9.98 (s, 1H); 13C NMR (50.3 MHz, CDCl3) δ -0.1, 13.9, 22.4,
30.5, 31.55, 126.8, 127.1, 127.5, 128.7, 134.0, 136.6, 140.7,
142.2, 148.8, 157.2, 193.2; GC-MS (EI) m/z (rel int) 322 (M+),
307 (60), 265 (75), 211 (29), 205 (30), 195 (34); 181 (26), 181
(26), 169 (67), 153 (29), 127 (100), 105 (22), 75 (75). Anal. Calcd
for C21H26OSi: C, 78.21; H, 8.13. Found: C, 78.22; H, 8.10.
2-[(Dim et h ylt h iop h en e-2-ylsila n yl)m et h ylen e]h exa -
n a l (Z)-1a f: colorless oil; IR (neat) 3075, 2956, 2929, 2859,
2735, 1686, 1585, 1466, 1406, 1253, 1214 cm-1; 1H NMR (200
MHz, CDCl3) δ 0.54 (s, 6H), 0.90 (t, J ) 7.3 Hz, 3H), 1.26-
1.44 (m, 4H), 2.30 (t, J ) 7.2 Hz, 2H), 6.88 (s, 1H), 7.18 (dd, J
) 3.3, 4.5 Hz, 1H), 7.29 (dd, J ) 0.6, 3.3 Hz, 1H), 7.62 (dd, J
) 0.6, 4.5 Hz, 1H) 9.82 (s, 1H); 13C NMR (50.3 MHz, CDCl3) δ
1.1, 13.9, 22.0, 30.5, 31.6, 128.4, 131.5, 135.1, 137.5, 147.9,
175.4, 193.1; GC-MS (EI) m/z (rel int) 252 (M+), 237 (56), 195
(100), 177 (19), 135 (26), 111 (13), 98 (14), 75 (20). Anal. Calcd
for C13H20OSSi: C, 61.85; H, 7.99. Found: C, 61.83; H, 7.96.
4-Br om o-2-[(d im eth ylp h en ylsilyl)m eth ylen e]bu ta n a l
(Z)-1ea : colorless oil; IR (neat) 3067, 2954, 2808, 1687, 1594,
2-(4-Meth oxyben zyl)h exa n a l, 4a d : colorless oil; IR (neat)
2956, 2932, 2712, 1725, 1513, 1248 cm-1; 1H NMR (200 MHz,
CDCl3) δ 0.86 (t, J ) 6.6 Hz, 3H), 1.21-1.33 (m, 2H), 1.39-
1.50 (m, 2H); 1.55-1.65 (m, 2H), 2.49-2.58 (m, 1H), 2.65 (dd,
J ) 7.5, 14.2 Hz, 1H), 2.89 (dd, J ) 7.5, 14.2 Hz, 1H), 3.75 (s,
3H), 6.79 (d, J ) 8.7 Hz, 2H), 7.05 (d, J ) 8.7 Hz, 2H) 9.62 (d,
J ) 2.7, 1H); 13C NMR (50.3 MHz, CDCl3) δ 13.8, 22.7, 28.3,
29.1, 34.2, 53.6, 55.2, 113.9, 129.9, 130.8, 158.1, 205.0; GC-
1
1428, 1250, 1106 cm-1; H NMR (200 MHz, CDCl3) δ 0.54 (s,
J . Org. Chem, Vol. 68, No. 24, 2003 9297

Aronica et al.
MS (EI) m/z (rel int) 221 (M+ + 1) 163 (4), 121 (100), 91 (5),
77 (5), 41 (13). Anal. Calcd for C13H18O2: C, 76.33; H, 9.15.
Found: C, 76.31; H, 9.18.
NMR (200 MHz, CDCl3) δ 1.06-1.12 (m, 2H), 1.25-1.31 (m,
2H), 3.12 (s, 2H); 7.27-7.42 (m, 5H), 8.87 (s, 1H); 13C NMR
(50.3 MHz, CDCl3) δ 12.7, 32.6, 34.9, 126.2, 128.2, 129.3, 138.6,
201.3; GC-MS (EI) m/z (rel int) 160 (M+), 159 (28), 142 (39),
129 (52), 103 (16), 91 (100), 77 829), 65 (33), 51 (17). Anal.
Calcd for C11H12O: C, 82.46; H, 7.55. Found: C, 82.41; H, 7.52.
1-Ben zylcyclop en ta n eca r ba ld eh yd e, 4fa : colorless oil;
2-Bip h en yl-4-ylm et h ylh exa n a l 4a e: colorless oil; IR
(neat) 2956, 2929, 2710, 1724, 1487, 1261 cm-1; 1H NMR (200
MHz, CDCl3) δ 0.93 (t, J ) 7.0 Hz, 3H), 1.28-1.82 (m, 6H),
2.58-2.72 (m, 1H), 2.78 (dd, J ) 6.6, 13.5 Hz, 1H), 3.05 (dd, J
) 6.6, 13.5 Hz, 1H), 7.23-7.63 (m, 9H) 9.70 (d, J ) 2.6, 1H);
13C NMR (50.3 MHz, CDCl3) δ 13.8, 22.6, 28.3, 29.0, 34.5, 53.3,
126.9, 127.10, 127.13, 128.7, 129.3, 137.9, 139.2, 140.7, 204.6;
GC-MS (EI) m/z (rel int) 266 (M+), 209 (9), 167 (100), 152
(12), 115 (4). Anal. Calcd for C19H22O: C, 85.67; H, 8.32.
Found: C, 85.69; H, 8.35.
IR (neat) 2721, 1948, 1877, 1809, 1720.cm-1 1H NMR (200
;
MHz, CDCl3) δ 1.48-1.68 (m, 6H), 1.85-1.95 (m, 2H), 2.91 (s,
2H), 7.09-7.27 (m, 5H), 9.56 (s, 1H); 13C NMR (50.3 MHz,
CDCl3) δ 24.8, 32.3, 41.1, 59.1, 126.4, 128.2, 129.8, 137.9, 205.0;
GC-MS (EI) m/z (rel int) 188 (M+), 91(100), 41 (16), 39 (19).
Anal. Calcd for C13H16O: C, 82.94; H, 8.57. Found: C, 82.91;
H, 8.53.
2-Th iop h en e-2-ylm et h ylh exa n a l, 4a f: colorless oil; IR
(neat) 3103, 3067, 2958, 2911, 2859, 2714, 1726, 1456 cm-1
;
Syn th esis of 2-Meth ylen eh exa n a l 12a a . To a solution of
2 mmol of (Z)-1a a in 10 mL of absolute EtOH, cooled at 0 °C,
were added 3 mmol of NaBH4. The suspension was stirred at
room temperature for 3 h, hydrolyzed with water and extracted
with dichloromethane. The organic layers were dried over Na2-
SO4 and then concentrated under vacuum. The crude 2-[(dim-
ethylphenylsilyl)methylene]hexan-1-ol (Z)-2a a was dissolved
in 10 mL of DMSO and treated with 2 mL of TBAF (1 M in
THF). The solution was heated at 60 °C for 2 h, hydrolyzed
(H2O), and extracted with Et2O. The organic fractions were
dried over Na2SO4 and evaporated in vacuo, and the crude
2-methylenehexan-1-ol 11a a was added to a solution of PDC
(6 mmol in 10 mL of DMF and 10 mL of CH2Cl2). The solution
was stirred for 2 h, hydrolyzed with water, and extracted with
pentane. The organic layers were dried (Na2SO4), and the
solvent was removed under vacuum. The crude 2-methylene-
hexanal 12a a was purified by column chromatography on silica
gel using hexane/EtOAc (95/5) as eluent affording 0.20 g (1.8
mmol, 90%) of pure aldehyde.
1H NMR (200 MHz, CDCl3) δ 0.87 (t, J ) 6.6 Hz, 3H), 1.24-
1.38 (m, 2H), 1.46-1.60 (m, 2H); 1.62-1.74,(m, 2H), 2.56-
2.66 (m, 1H), 2.95 (dd, J ) 6.3, 15.0 Hz, 1H), 3.18 (dd, J )
6.3, 15 Hz, 1H), 6.76-6.78 (m, 1H), 6.89 (dd, J ) 3.3, 5.1 Hz,
1H) 7.11 (dd, J ) 1.2, 5.1 Hz, 1H) 9.66 (d, J ) 2.4, 1H); 13C
NMR (50.3 MHz, CDCl3) δ 13.8, 22.7, 28.2, 28.8, 28.9, 53.4,
123.8, 125.6, 126.9, 141.3, 204.1; GC-MS (EI) m/z (rel int) 196
(M+), 139 (17), 111 (13), 97 (100), 84 (27). Anal. Calcd for
C
11H16OS: C, 67.30; H, 8.22. Found: C, 67.31; H, 8.26.
2-Ben zyl-3-m et h ylbu t a n a l 4b a : colorless oil; IR (neat)
2717, 1949, 1877, 1804, 1724 cm-1; 1H NMR (200 MHz, CDCl3)
δ 1.04 (d, J ) 7 Hz, 6H), 2.06 (m, 1H), 2.45-2.56 (m, 1H),
2.75 (dd, J ) 14.0, 2.7 Hz, 1H), 2.99 (dd, J ) 14.0, 9.2 Hz,
1H), 7.10-7.32 (m, 5H), 9.68 (d, J ) 2.6 Hz, 1H); 13C NMR
(50.3 MHz, CDCl3) δ 19.7, 19.9, 28.2, 31.9, 59.6, 126.1, 128.4,
128.8, 139.6, 204.9; GC-MS (EI) m/z (rel int) 133 (M+ - 43),
105 (9), 91 (50), 65 (11), 56 (20), 52 (21), 43 (42), 41 (92), 39
(100). Anal. Calcd for C12H16O: C, 81.77; H, 9.15. Found: C,
81.75; H, 9.18.
2-[(Dim eth ylph en ylsilyl)m eth ylen e]h exa n -1-ol (Z)-2a a :
1
2-Ben zyl-3-m eth ylpen tan al 4ca (diaster eoisom er ic m ix-
tu r e, 50:50): colorless oil; IR (neat) 2719, 1945, 1879, 1802,
1724, 1705 cm-1; 1H NMR (200 MHz, CDCl3) δ 0.83-1.04 (m,
12H), 1.2-2.0 (m, 6H), 2.56-3.10 (m, 6H), 7.1-7.3 (m, 10H);
9.66 (d, J ) 2.3 Hz, 1H), 9.72 (d, J ) 2.3 Hz, 1H); 13C NMR
(50.3 MHz, CDCl3) δ 11.7 and 11.8, 16.0 and 16.2, 27.0, 30.6
and 32.2, 34.5 and 35.3, 58.0 and 58.2, 126.1 and 126.2, 128.3
and 128.4, 128.7 and 128.8, 139.6 and 139.9, 204.7 and 205.1;
GC-MS (EI) m/z (rel int) (1 diastereoisomer), 133 (M+ - 57),
115 (10), 91 (55), 77 (3), 65 (6), 56 (29), 43 (29), 41 (100); GC-
MS (EI) m/z (rel int) (1 diastereoisomer) 133 (M+ - 57), 105
(8), 91 (66), 65 (8), 56 (13), 43 (35), 41 (100), 39 (79). Anal.
Calcd for C13H18O: C, 82.06; H, 9.53. Found: C, 82.03; H, 9.55.
2-Ben zyl-3-p h en ylbu ta n a l 4d a (d ia ster eoisom er ic m ix-
tu r e, 50:50): colorless oil; IR (neat) 2721, 1945, 1877, 1792,
colorless oil; IR (neat) 3354; 1614; 1427; 1248 cm-1; H NMR
(200 MHz, CDCl3) δ 0.36 (s, 6H), 0.91 (t, J ) 7.0 Hz, 3H), 1.03
(s, 1H), 1.22-1.52 (m, 4H), 2.50 (t, J ) 7.0 Hz, 2H), 3.97 (s,
2H), 5.55 (s, 1H), 7.32-7.35 (m, 3H), 7.45-7.55 (m, 2H); 13C
NMR (50.3 MHz, CDCl3) δ 0.5, 13.9, 22.5, 30.4, 36.9, 65.2,
124.2, 127.9, 128.9, 133.5, 140.3, 159.0; GC-MS (EI) m/z (rel
int) 233 (M+-15), 215 (9), 171 (9), 145 (16), 155 (25), 137 (71),
135 (86), 121 (17), 105 (19), 91 (12), 75 (100), 61 (29), 43 (48).
Anal. Calcd for C15H24OSi: C, 72.52; H, 9.74. Found: C, 72.50;
H, 9.77.
2-Meth ylen eh exa n -1-ol 11a a :24 colorless oil; 1H NMR (200
MHz, CDCl3) δ 0.89 (t, J ) 6.9 Hz, 3H), 1.23-1.50 (m, 4H),
2.10 (t, J ) 8.0 Hz, 2H), 4.05 (s, 2H), 4.80-4.88 (m, 1H), 4.92-
5.00 (m, 1H); 13C NMR (50.3 MHz, CDCl3) δ 13.9, 22.5, 30.0,
32.7, 66.9, 109.0, 149.3.
1
1
1724 cm-1; H NMR (200 MHz, CDCl3) δ 1.31 (d, J ) 6.9 Hz,
2-Meth ylen eh exa n a l 12a a :25 colorless oil; H NMR (200
3H), 1.39 (d, J ) 6.9, 3H), 2.55-3.31 (m, 8H), 7.00-7.40 (m,
20H), 9.57 (d, J ) 3 Hz, 1H), 9.65 (d, J ) 3 Hz, 1H); 13C NMR
(50.3 MHz, CDCl3) δ 18.2 and 19.4, 32.4 and 34.3, 39.9 and
40.1, 59.6 and 59.9, 126.3 and 126.3, 126.9, 127.5 and 127.7,
128.5 and 128.6, 128.7 and 128.9, 136.8 and 139.2, 143.8, 204.2
and 204.7; GC-MS (EI) m/z (rel int) (1 diastereoisomer), 220
(M+ - 18), 147 (10), 133 (80), 115 (10), 105 (100), 91 (54), 77
(16), 65 (11), 51 (15); GC-MS (EI) m/z (rel int) (1 diastereo-
isomer), 220 (M+ - 18), 147 (23), 133 (75), 115 (9), 105 (100),
91 (62), 77 (19), 65 (12), 51 (15). Anal. Calcd for C17H18O: C,
85.67; H, 7.61. Found: C, 85.66; H, 7.63.
MHz, CDCl3) δ 0.91 (t, J ) 6.9 Hz, 3H), 1.26-1.52 (m, 4H),
2.25 (t, J ) 6.8 Hz, 2H), 5.98 (s, 1H), 6.24 (s, 1H), 9.54 (s, 1H).
Ack n ow led gm en t. Financial support for this work
was provided by the Ministero dell’Istruzione, dell’Uni-
versita` e della Ricerca (MIUR PRIN 2001 project no.
2001038991).
J O0351062
(24) Barluenga, J .; Fernandez-Simon, J . L.; Concellon, J . M.; Yus,
M. J . Chem. Soc., Perkin Trans. 1 1989, 77-80.
(25) Alexakis, A.; Commercon, A.; Coulentianos, C.; Normant, J . F.
Tetrahedron 1984, 40, 715-731.
1-Ben zylcyclop r op a n eca r ba ld eh yd e, 4ea : colorless oil;
1
IR (neat) 2919, 2728, 2080, 1947, 1879, 1708, 1495 cm-1; H
9298 J . Org. Chem., Vol. 68, No. 24, 2003