One-pot multicoupling reaction of silylcopper reagents, organolithium compounds and α,β-unsaturated nitriles

Article abstract of DOI:10.1039/c0ob00775g

The silylcupration of allene using a lower order silylcopper species gives an allylsilane-vinyl copper intermediate 2 which, in conjunction with an organolithium reagent, is able to participate in a one-pot multicoupling reaction with α,β-unsaturated nitr

Full text of DOI:10.1039/c0ob00775g

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PAPER
One-pot multicoupling reaction of silylcopper reagents, organolithium
compounds and a,b-unsaturated nitriles†
Francisco J. Pulido,* Asuncio´n Barbero* and Yolanda Blanco
Received 24th September 2010, Accepted 22nd November 2010
DOI: 10.1039/c0ob00775g
The silylcupration of allene using a lower order silylcopper species gives an allylsilane–vinyl copper
intermediate 2 which, in conjunction with an organolithium reagent, is able to participate in a one-pot
multicoupling reaction with a,b-unsaturated nitriles. The scope of this tandem reaction is studied and a
possible mechanism pathway is outlined.
Introduction
The development of new strategies directed to the efficient
introduction of various functionalized groups into a molecule,
with a minimum of chemical steps, constitutes one of the subjects
of increasing interest in the synthesis of complex structures.
In this sense, there have been many attempts to achieve the
consecutive introduction of various reagents into a substrate
in a single operation, the so-called multicomponent one-pot-
reactions. Thus, Gaudemar,1 Knochel,2,3 and Normant’s groups4,5
have described the synthesis of gem-dimetallic reagents via a
carbometallation process of vinyl organometallics with allylic
zinc bromides.6 The dimetallic reagents, containing two metals of
different nature and reactivity, show good chemoselectivity in the
presence of two different electrophiles to give the corresponding
multicoupled products in good yields. This reaction works even
when the two different electrophiles are added simultaneously to
the dimetallic reaction media (Scheme 1).
Scheme 1 Reactivity of gem-dimetallic reagents.
On the other hand, Nakamura7 has reported that the si-
multaneous addition of two different electrophiles to a novel
dimetallated hydrazone provides chemoselectively the product of
double trapping, in nearly quantitative yield.
to their remarkable versatility and synthetic utility. For the last
decade, we have been involved in the study of the silylcupration
of allenes13,14 and in the development of new strategies, using the
allylsilanes thus obtained, for the synthesis of carbocycles15,16 of
close structure to some natural products (Scheme 2).
Thus, in the course of the study of the silylcupration of allene,
followed by capture of the intermediate allylsilane–vinylcuprate
2 with a,b-unsaturated nitriles17 we discovered an interesting
stepwise one-pot conversion of alkenenitriles to the corresponding
products of double 1,2 and 1,4-diaddition.
A different approach to a one-pot multicoupling reaction has
been described by de Meijere8 in his synthesis of primary amines by
the consecutive addition of two equivalents of a Grignard reagent
to a nitrile, in the presence of Ti(OiPr)4. However, the reaction is
low-yielding when two different Grignard reagents are used.
Another example of this strategy has been reported by
Shimizu,9,10 who developed an efficient method for the intro-
duction of two different nucleophiles into an a,b-unsaturated
aldimine, to give functionalized amines in a one-pot procedure.
On the other hand, allylsilanes have been extensively used as
building blocks in the construction of natural products,11,12 due
In this paper we describe an efficient method for the selective
double nucleophilic addition of two different organometallics to
a,b-unsaturated nitriles to give the products of double addition in
an efficient one-pot procedure.
Results and discussion
Departamento de Qu´ımica Orga´nica, Facultad de Ciencias, C/Dr
Mergelina s/n, 47011, Valladolid, SPAIN. E-mail: pulido@qo.uva.es,
barbero@qo.uva.es; Fax: +34-983-423013; Tel: +34-983-423210
† We are pleased to dedicate this article to Professor Carmen Na´jera on
the occasion of her 60th birthday.
Thus, the addition of a,b-unsaturated nitriles to an equimolar mix-
ture of an organolithium reagent and an allylsilane—vinylcopper
intermediate 2, generated by reaction of allene with the lower
1454 | Org. Biomol. Chem., 2011, 9, 1454–1458
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Table 1 Scope of the multicoupling reaction
Nitrile
R1
Organolithium
R3
R2
SiR3
Product
Yield (%)a
t
H
H
Me
Et
Ph
H
H
H
Me
Me
Me
H
H
H
Me
Me
Me
H
Me
Bu
Bu
Bu
Bu
Bu
Ph
Allyl
Me
SiPh2 Bu
3a
3b
3c
3d
3e
3f
3g
3h
3i
58
50
55
60
57
50
49
40
51
t
SiPh2 Bu
t
SiPh2 Bu
t
SiPh2 Bu
t
SiPh2 Bu
t
SiPh2 Bu
SiMe2Ph
SiMe2Ph
SiMe2Ph
a The allylsilane of hydrolysis
byproduct.
was isolated, as the major
the products of 1,4-monoaddition 4 or the products of 1,2-
monoaddition 5 (Scheme 4), which seems to indicate that the
reaction of the intermediate monoaddition product with the
remaining organometallic is very fast.
Scheme 2 Allylsilanes as intermediates in the synthesis of carbocycles.
order tert-butyldiphenylsilylcopper or phenyldimethylsilylcopper
1, provides functionalized ketones 3 in good yields over two steps
(Scheme 3).
Scheme 4 The products of monoaddition couldn’t be isolated.
From these results we propose a plausible reaction mechanism
as shown in Scheme 5. Thus, the initial 1,2-addition of the more
reactive organolithium reagent to the vinyl nitrile would generate
an a,b-unsaturated imine intermediate, which in turn is attacked
by the allylsilane–vinylcopper 2 in a conjugate addition to give,
after final hydrolysis, the product of double nucleophilic addition
3 (Scheme 5).
Scheme 3 Double nucleophilic addition of different organometallics to
a,b-unsaturated nitriles.
To study the scope of this interesting process we have used
a wide variety of organolithium reagents, different substituted
nitriles and silyl groups of different nature (Table 1). As we observe
from results quoted in Table 1, both aryl-substituted and alkyl-
substituted acrylonitriles undergo this sequential double addition.
On the other hand, the use of alkyllithium reagents provides the
best yields of the double addition product, though the reaction
also works when aryllithium or allyllithium is used. Moreover,
both phenyldimethylsilyl and tert-butyldiphenylsilyl groups give
satisfactorily the tandem reaction (Table 1).
Interestingly, the different nature of the two metals (lithium
and copper) in both organometallics was used in a chemoselective
manner to create successively two new bonds in their reaction with
alkenenitriles. Thus, since carbon–copper and carbon–lithium (or
carbon–magnesium) bonds show very different reactivities, they
are able to add stepwise to an electrophile with two reactive
sites, such as the a,b-unsaturated nitrile, affording the products
of double 1,2- and a 1,4-diaddition. We couldn’t isolate either
Scheme 5 Mechanism of the reaction.
Finally, we examined the validity of this protocol when a Grig-
nard reagent is used instead of the organolithium reagents. Results
are summarized in Scheme 6. As we can see organomagnesium
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1
885; H NMR (300 MHz, CDCl3) d (ppm): 7.76–7.27 (m, 10H,
2¥Ph), 4.74 (s, 1H, CHH ), 4.60 (s, 1H, CHH ), 2.56–2.44 (m,
1H, CH), 2.31 (d, J = 13.7 Hz, 1H, CHH–Si), 2.16 (d, J = 13.7 Hz,
1H, CHH-Si), 2.02 (dd, J = 14.5 and 6.5 Hz, 1H, CHH–C ), 1.90
(s, 3H, CH3-CO), 1.63 (dd, J = 14.5 and 7.9 Hz, 1H, CHH-C ),
t
1.11 (s, 9H, Bu), 0.84 (d, J = 6.9, 3H, CH3-CH); 13C NMR (75
MHz, CDCl3) d (ppm): 212.3, 143.9, 136.1, 134.6, 129.2, 127.5,
112.3, 44.9, 41.3, 27.7, 20.0, 18.6, 15.8; MS (EI): m/z 349 (M+ -
t
CH3, 34%), 307 (M+ - Bu, 5%), 239 (tBuPh2Si, 12%); Anal. Calcd
for C24H32OSi: C, 79.06; H, 8.85; Found: C, 79.45; H, 8.56%.
2-[(tert-Butyldiphenylsilyl)methyl]-4-methyl-1-nonen-5-one (3b).
Colorless oil; Yield (50%); IR nmax(film)/cm-1 1714, 1632, 1256,
1105, 885; H NMR (300 MHz, CDCl3) d (ppm): 7.68–7.27 (m,
Scheme 6 Multicoupling reaction using Grignard reagents.
1
10H, 2¥Ph), 4.71 (s, 1H, CHH ), 4.57 (s, 1H, CHH ), 2.55–
2.44 (m, 1H, CH-CO), 2.25 (d, J = 14.3 Hz, 1H, CHH-Si), 2.20
(d, J = 14.3 Hz, 1H, CHH–Si), 2.15 (t, J = 7.3 Hz, 2H, CH2-CO),
2.00 (dd, J = 14.3 and 6.8 Hz, 1H, CHH-CH), 1.57 (dd, J = 14.3
and 7.8 Hz, 1H, CHH-CH), 1.49-1.41 (m, 2H, CH2), 1.39–1.15
(m, 2H, CH2-CH3), 1.09 (s, 9H, 3¥CH3), 0.89 (t, J = 7.2 Hz, 3H,
CH3-CH2), 0.80 (t, J = 6.9 Hz, 3H, CH3-CH); 13C NMR (75 MHz,
CDCl3) d (ppm): 214.3, 144.0, 136.1, 134.7, 129.1, 127.5, 112.3,
44.1, 41.3, 40.5, 27.7, 25.5, 22.2, 20.0, 18.6, 15.9, 13.9; MS (EI):
m/z 406 (M+, 10%), 391 (M+ - CH3, 5%), 349 (M+ - Bu, 17%),
239 (tBuPh2Si, 10%); Anal. Calcd for C27H38OSi: C, 79.74; H, 9.42;
Found: C, 80.11; H, 9.73%.
reagents are also effective for promoting the reaction, though
yields are slightly lower (Scheme 6).
Conclusions
In summary, this paper describes
a four component re-
action by double nucleophilic addition of two differ-
a
ent organometallics (organolithium/organomagnesium and an
allylsilane–vinylcopper reagent) to a,b-unsaturated nitriles to
give, in a one-pot procedure, functionalized oxoallylsilanes. This
methodology provides a quick one-pot assembly of equimolar
amounts of four substrates: allene, a silylcopper reagent, an
organolithium reagent and a nitrile.
2-[(tert-Butyldiphenylsilyl)methyl]-3-methyl-1-nonen- 5-one (3c).
Colorless oil; Yield (55%); IR nmax(film)/cm-1 1713, 1633, 1106,
1
925; H NMR (300 MHz, CDCl3) d (ppm): 7.67–7.27 (m, 10H,
Experimental
2¥Ph), 4.60 (s, 1H, CHH ), 4.55 (s, 1H, CHH ), 2.30–2.09 (m,
5H, CH3–CH, 2¥CH2-CO), 2.19 (s, 2H, CH2–Si), 1.45 (quintet,
J = 7.3 Hz, 2H, CH2-CH2), 1.40–1.10 (m, 2H, CH2–CH2), 1.06 (s,
9H, 3¥CH3), 0.89 (t, J = 7.2 Hz, 3H, CH3-CH2), 0.79 (d, J = 6.2
Hz, 3H, CH3-CH); 13C NMR (75 MHz, CDCl3) d (ppm): 210.4,
150.5, 136.2, 134.4, 129.0, 127.4, 108.8, 48.9, 42.4, 36.6, 27.8, 25.7,
22.2, 19.2, 18.6, 18.5, 13.8; MS (EI): m/z 406 (M+, 7%), 391 (M+
- CH3, 7%), 349 (M+ - Bu, 20%), 239 (tBuPh2Si, 13%).
General experimental
All the reactions were carried out under an atmosphere of argon or
nitrogen in dried glassware unless otherwise indicated. Materials
were obtained from commercial suppliers and used without further
purification except when otherwise noted. Solvents were dried
and distilled according to the standard protocols. Flash column
chromatography was performed on silica gel using the indicated
solvent.
2-[(tert-Butyldiphenylsilyl)methyl]-3-ethyl-1-nonen- 5-one (3d).
Colorless oil; Yield (60%); IR nmax(film)/cm-1 1714, 1636, 1256,
1
1105, 876; H NMR (300 MHz, CDCl3) d (ppm): 7.69–7.27 (m,
General procedure for one-pot double addition
10H, 2¥Ph), 4.62 (s, 1H, CHH ), 4.55 (s, 1H, CHH ), 2.33–
2.10 (m, 3H, CH and CH–CH2-CO), 2.17 (t, J = 7.1 Hz, 2H,
CH2-CO), 2.17 (s, 2H, CH2- Si), 1.45-1.3 (m, 2H, CH2-CH), 1.28–
0.9 (m, 4H, CH2-CH2), 1.03 (s, 9H, 3xCH3), 0.88 (t, J = 7.3 Hz,
3H, CH3-CH2), 0.65 (t, J = 7.4 Hz, 3H, CH3-CH2-CH); 13C NMR
(75 MHz, CDCl3) d (ppm): 210.6, 147.9, 136.2, 134.4, 129.0, 127.4,
111.4, 46.8, 43.7, 42.5, 27.8, 25.8, 25.7, 22.3, 18.4, 17.6, 13.9, 11.0;
MS (EI): m/z 420 (M+, 2%), 391 (M+ - Et, 12%), 363 (M+ - Bu,
15%), 239 (tBuPh2Si, 13%); Anal. Calcd for C28H40OSi: C, 79.94;
H, 9.58; Found: C, 79.58; H, 9.85%.
A solution of dimethylphenylsilyl-lithium (6 mmol) in THF was
added by syringe to a stirred suspension of copper(I) cyanide
(6 mmol) in THF at 0 ◦C. After 30 min at this temperature the
solution of silylcopper 1 (6 mmol) was cooled at -40 ◦C and a
slight excess of allene was added from a balloon. The mixture was
stirred for 1 h and then used immediately.
The organolithium or Grignard reagent (6 mmol) was added to
this solution at -60 ◦C and then 6 mmol of BF3·Et2O was added
to the mixture and stirred for an additional period of 10 min.
The nitrile (6 mmol) in THF was slowly dropped in at -60 ◦C
and stirred at this temperature for 1 h. The reaction mixture was
2-[(tert-Butyldiphenylsilyl)methyl)]-3-phenyl-1-nonen-5-one (3e).
Colorless oil; Yield (57%); IR nmax(film)/cm-1 1717, 1632, 1245,
◦
allowed to warm to 0 C, quenched with basic saturated ammo-
1
1104, 925; H NMR (300 MHz, CDCl3) d (ppm): 7.67–7.27 (m,
nium chloride solution and extracted with ether. The organic layer
was dried (MgSO4), evaporated and chromatographed to give the
corresponding products.
10H, 2¥Ph), 7.25–6.98 (m, 5H, Ph), 4.75 (s, 1H, CHH ), 4.73 (s,
1H, CHH ), 3.37 (dd, J = 9.6 and 5.2 Hz, 1H, CH-Ph), 2.62 (dd,
J = 15.5 and 9.6 Hz, 1H, CHH-CH), 2.43 (dd, J = 15.5 and 5.2
Hz, 1H, CHH-CH), 2.19 (d, J = 15.0 Hz, 1H, CHH-Si), 2.11–1.92
(m, 2H, CH2–CO), 1.87 (d, J = 15.0 Hz, 1H, CHH–Si), 1.34–1.16
5-[(tert-Butyldiphenylsilyl)methyl]-3-methyl-5-hexen-2-one (3a).
Colorless oil; Yield (58%); IR nmax(film)/cm-1 1715, 1633, 1105,
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(m, 2H, CH2- CH2), 1.15–1.04 (m, 2H, CH2-CH3), 1.00 (s, 9H,
3¥CH3), 0.79 (t, J = 7.2 Hz, 3H, CH3-CH2); 13C NMR (75 MHz,
CDCl3) d (ppm): 209.1, 148.1, 142.3, 136.3, 136.2, 134.5, 134.3,
129.1, 129.0, 128.2, 127.4, 126.4, 110.1, 47.9, 47.8, 42.6, 27.7, 25.4,
22.1, 19.1, 18.4, 13.7; MS (EI): m/z 391 (M+ - Ph, 8%), 411 (M+ -
Bu, 20%), 239 (tBuPh2Si, 19%); Anal. Calcd for C32H40OSi: C,
81.99; H, 8.60; Found: C, 82.32; H, 8.89%.
0.97 (d, J = 6.6 Hz, 3H, CH3-CH), 0.35 (s, 3H, CH3–Si), 0.34 (s,
3H, CH3–Si); 13C NMR (75 MHz, CDCl3) d (ppm): 208.2, 150.9,
138.9, 133.6, 129.0, 127.7, 106.6, 49.8, 36.3, 30.2, 25.0, 19.4, -2.9;
MS (EI): m/z 260 (M+, 10%), 245 (M+ - CH3, 100%), 217 (M+ -
CH3 - CO, 40%); Anal. Calcd for C16H24OSi: C, 73.79; H, 9.29;
Found: C, 74.18; H, 9.58%.
5-[(Dimethylphenylsilyl)methyl)]-4-ethyl-5-hexen-2-one
(3j).
Colorless oil; Yield (49%); IR nmax(film)/cm-1 1710, 1630, 1241,
2-[(Dimethylphenylsilyl)methyl)]-4-methyl-1-nonen-5-one (3f).
1
Colorless oil; Yield (50%); IR nmax(film)/cm-1 1714, 1631, 1249,
1111, 878; H NMR (300 MHz, CDCl3) d (ppm): 7.56–7.27 (m,
1
5H, Ph), 4.76 (s, 1H, CHH ), 4.73 (s, 1H, CHH ), 2.48–2.22
(m, 3H, CH2-CO, CH), 2.04 (s, 3H, CH3-CO), 1.73 (s, 2H,
CH2–Si), 1.55 (quint, J = 6.5 Hz, 2H, CH2-CH3), 0.80 (t, J = 7.5
Hz, 3H, CH3-CH2), 0.36 (s, 3H, CH3–Si), 0.35 (s, 3H, CH3–Si);
13C NMR (75 MHz, CDCl3) d (ppm): 211.5, 146.1, 138.3, 133.5,
129.2, 127.8, 109.6, 48.9, 44.0, 27.8, 25.3, 21.3, 11.1, -2.9; MS
(EI): m/z 274 (M+, 8%), 259 (M+ - CH3, 100%), 231 (M+ - CH3 -
CO, 20%); Anal. Calcd for C17H26OSi: C, 74.39; H, 9.55; Found:
C, 74.73; H, 9.86%.
1112, 885; H NMR (300 MHz, CDCl3) d (ppm): 7.56–7.27 (m,
5H, Ph), 4.58 (s, 2H, CH2 ), 2.67–2.59 (m, 1H, CH), 2.33–2.26
(m, 2H, CH2-CO), 2.19 (dd, J = 14.4 and 6.7 Hz, 1H, CHH-CH),
1.76 (d, J = 13.6 Hz, 1H, CHH-Si), 1.75 (dd, J = 14.4 and 7.8 Hz,
1H, CHH-CH), 1.71 (d, J = 13.6 Hz, 1H, CHH-Si), 1.52–1.44
(m, 2H, CH2), 1.34–1.23 (m, 2H, CH2), 0.96 (d, J = 6.8 Hz,
3H, CH3-CH), 0.90 (t, J = 7.2 Hz, 3H, CH3-CH2), 0.33 (s, 6H,
2¥CH3–Si); 13C NMR (75 MHz, CDCl3) d (ppm): 214.4, 144.1,
138.8, 133.5, 129.2, 127.5, 110.0, 44.2, 41.3, 40.9, 26.9, 25.6, 22.3,
16.1, 13.9, -3.0, -3.2; MS (EI): m/z 302 (M+, 28%), 287 (M+ -
CH3, 8%), 273 (M+ - Et, 4%), 245 (M+ - Bu, 18%), 167 (M+ -
SiMe2Ph, 13%), 135 (SiMe2Ph, 100%), 57 (Bu, 5%); Anal. Calcd
for C19H30OSi: C, 75.43; H, 10.00; Found: C, 75.78; H, 9.67%.
3-[(Dimethylphenylsilyl)methyl)]-2-ethyl-3-butenyl phenyl ketone
(3k). Colorless oil; Yield (52%); IR nmax(film)/cm-1 1720, 1635,
1243, 1110, 881; 1H NMR (300 MHz, CDCl3) d (ppm): 7.61–7.24
(m, 10H, 2¥Ph), 4.66 (s, 1H, CHH ), 4.64 (s, 1H, CHH ), 2.96
(dd, J = 16.2 and 6.1 Hz, 1H, CHH-CO), 2.89 (dd, J = 16.2 and 7.0
Hz, 1H, CHH-CO), 2.41-2.32 (m, 1H, CH), 1.76 (s, 2H, CH2–Si),
1.08–1.01 (m, 2H, CH2-CH3), 0.79 (t, J = 7.4 Hz, 3H, CH3-CH2),
0.34 (s, 6H, 2¥CH3–Si); 13C NMR (75 MHz, CDCl3) d (ppm):
206.0, 149.1, 139.6, 133.2, 133.0, 129.0, 128.6, 128.1 127.6, 109.5,
53.6, 43.2, 29.4, 24.6, 10.9, 3.1; MS (EI): m/z 336 (M+, 12%), 321
(M+ - CH3, 100%), 259 (M+ - Ph, 30%).
3-[(Dimethylphenylsilyl)methyl)]-1-methyl-3-butenyl phenyl ke-
tone (3g). Colorless oil; Yield (49%); IR nmax(film)/cm-1 1688,
1
1630, 1251, 1110, 878; H NMR (300 MHz, CDCl3) d (ppm):
7.58–7.27 (m, 10H, 2¥Ph), 4.63 (s, 1H, CHH ), 4.59 (s, 1H,
CHH ), 3.61 (sextet, J = 6.9 Hz, 1H, CH), 2.44 (dd, J = 14.8
and 6.5 Hz, 1H, CHH-C ), 1.95 (dd, J = 14.8 and 7.3 Hz, 1H,
CHH–C ), 1.82 (d, J = 13.7 Hz, 1H, CHH-Si), 1.76 (d, J = 13.7
Hz, 1H, CHH–Si), 1.14 (d, J = 6.9 Hz, 3H, CH3-CH), 0.34 (s,
3H, CH3–Si), 0.32 (s, 3H, CH3–Si); 13C NMR (75 MHz, CDCl3) d
(ppm): 215.2, 144.2, 136.5, 133.5, 132.8, 129.0, 128.6, 128.2, 127.7,
109.7, 41.6, 38.7, 26.0, 17.3, -3.0; MS (EI): m/z 322 (M+, 5%), 307
(M+ - CH3, 19%), 245 (M+ - Ph, 25%), 135 (SiMe2Ph, 100%);
Anal. Calcd for C21H26OSi: C, 78.21; H, 8.13; Found: C, 77.89; H,
8.41%.
Acknowledgements
We thank the Ministry of Science and Technology of Spain
(CTQ2009-09302) and the ‘Junta de Castilla y Leo´n’ (GR170 and
VA074A08) for financial support.
Notes and references
7-[(Dimethylphenylsilyl)methyl)]-5-methyl-1,7-octadien-4-one
(3h). Colorless oil; Yield (40%); IR nmax(film)/cm-1 1710, 1634,
1251, 1112, 885; 1H NMR (300 MHz, CDCl3) d (ppm): 7.60–7.27
(m, 5H, Ph), 5.86 (ddt, J = 17.1, 10.3 and 6.9 Hz, 1H, CH ), 5.15
(d, J = 10.3 Hz, 1H, CHH ), 5.08 (d, J = 17.1 Hz, 1H, CHH ),
4.59 (s, 2H, CH2 ), 3.08 (d, J = 6.9 Hz, 2H, CH2-CO), 2.72–2.63
(m, 1H, CH-CO), 2.19 (dd, J = 14.5 and 6.7 Hz, 1H, CHH–C ),
1.78 (dd, J = 14.5 and 7.7 Hz, 1H, CHH-C ), 1.76 (d, J = 13.8 Hz,
1H, CHH-Si), 1.69 (d, J = 13.8 Hz, 1H, CHH–Si), 0.97 (d, J = 6.9
Hz, 3H, CH3-CH), 0.33 (s, 6H, 2¥CH3–Si); 13C NMR (75 MHz,
CDCl3) d (ppm): 211.9, 143.9, 138.8, 133.5, 130.8, 129.1, 127.8,
118.4, 110.2, 46.0, 43.8, 41.2, 25.6, 16.0, -2.9, -3.2; MS (EI): m/z
286 (M+, 13%), 271 (M+ - CH3, 10%), 135 (SiMe2Ph, 100%).
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C. P. Yeh and P. Knochel, Tetrahedron Lett., 1989, 30, 4799.
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5-[(Dimethylphenylsilyl)methyl)]-4-methyl-5-hexen-2-one (3i).
Colorless oil; Yield (51%); IR nmax(film)/cm-1 1720, 1633, 1240,
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1114, 878; H NMR (300 MHz, CDCl3) d (ppm): 7.58–7.27 (m,
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5H, Ph), 4.63 (s, 1H, CHH ), 4.57 (s, 1H, CHH ), 2.52 (dd, 1H,
J = 15.3 and 4.2 Hz, CHH-CO), 2.44–2.33 (m, 1H, CH), 2.27 (dd,
J = 15.3 and 8.8 Hz, 1H, CHH-CO), 2.04 (s, 3H, CH3-CO), 1.81
(d, J = 14.7 Hz, 1H, CHH-Si), 1.76 (d, J = 14.7 Hz, 1H, CHH-Si),
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