Tandem-directed regioselective hydroformylation/β-elimination: A practical method for the synthesis of enals

Article abstract of DOI:10.1055/s-2008-1067140

A practical synthesis of α,β-unsaturated aldehydes by a tandem-directed hydroformylation/β-elimination process of allylic o-DPPB esters is reported. The o-DPPB group served as an effective controller for regioselectivity of the hydroformylation towards th

Full text of DOI:10.1055/s-2008-1067140

PAPER
2169
Tandem-Directed Regioselective Hydroformylation/b-Elimination:
A Practical Method for the Synthesis of Enals
Synthesis of
Enals
c
via Regios
h
elective
H
yd
i
roform
m
ylation/
b
-Elimination Bruch, Antje Gebert, Bernhard Breit*
Institut für Organische Chemie und Biochemie, Albert-Ludwigs-Universität Freiburg, Albertstr. 21, 79104 Freiburg i. Breisgau, Germany
Fax +49(761)2038715; E-mail: bernhard.breit@organik.chemie.uni-freiburg.de
Received 8 April 2008
Dedicated to Professor Reinhard W. Hoffmann on the occasion of his 75th birthday
nates for efficient olefination of aldehydes and ketones.13
Abstract: A practical synthesis of a,b-unsaturated aldehydes by a
All of the described methods produce equimolar amounts
of coupled products and thus suffer from being not atom-
economic transformations. Hydroformylation, as an ex-
tandem-directed hydroformylation/b-elimination process of allylic
o-DPPB esters is reported. The o-DPPB group served as an effec-
tive controller for regioselectivity of the hydroformylation towards
the desired aldolate isomer, and was subsequently eliminated in situ ample for an atom economic reaction, would exhibit an el-
by mild standard bases. The reaction is rather general for the prep-
egant alternative for the synthesis of enals, but to the best
aration of 1,1-disubstituted and trisubstituted enals and is compati-
of our knowledge the only report in this area is the hydro-
ble with many functional groups. Recovery of the o-DPPBA is
formylation of alkynes by Buchwald, which can be ap-
possible either by chromatography or precipitation as the diethyl-
plied conveniently only to symmetrical substrates.14
ammonium salt.
We recently showed that with aid of the substrate-bound
directing o-DPPB (ortho-diphenylphosphanylbenzoate)
group efficient regio- and diastereocontrol in the course of
the hydroformylation of allylic, methallylic, and ho-
momethallyic alcohols can be achieved.15 In the case of
allylic o-DPPB-esters, the corresponding anti-o-DPPB al-
dolates were formed in high regio- and diastereoselectivi-
ty.16,17 In such aldolates the o-DPPB moiety is a potential
leaving group. Hence, a subsequent b-elimination of o-
DPPBA should afford the corresponding enals
(Scheme 1).
Key words: hydroformylation, enals, tandem reaction, aldehydes,
rhodium
a,b-Unsaturated aldehydes are an important class of or-
ganic compounds. Some of them occur in nature,1 others
are ingredients of flavors and fragrances,2 but most of
them are utilized as building blocks in organic synthesis.3
Despite their importance, the synthesis of enals is still
challenging. An excellent review summarizing most im-
portant synthetic routes has appeared recently.4 Most gen-
eral strategies rely on functional group interconversion
starting from a substrate with the complete carbon skele-
ton in place. Among these processes are oxidations of al-
lylic alcohols or reductions of a,b-unsaturated carboxylic
acid derivatives. Skeleton-expanding reactions for the
construction of enals are less frequently used. Among
those are the reactions of alkenyl organometallics with C1
electrophiles such as DMF,5 cross-metathesis reactions
employing acrolein,6 and cross-aldol condensation. The
latter is not a trivial task since self-aldolization of the
starting aldehyde can occur. This problem is circumvent-
ed using either azaenolates,7 silyl enolates,8 or cis-2-
ethoxyvinyllithium9 as the nucleophilic aldehyde counter-
part. Furthermore, enals are accessible by way of Wittig
olefination using formylmethylenetriphenylphospho-
ranes. The olefination proceeds generally well with elec-
tron-poor aldehydes, but fails with ketones.10,11 With
electron-rich aldehydes and ketones as electrophiles non-
stabilized ylides like the ones derived from 1,3-dioxan-2-
ylmethyltriphenylphosphonium bromide have been em-
ployed with some success.12 Nagata and Hayase used
deprotonated diethyl b-(cyclohexylimino)ethyl phospho-
O
(o-DPPB)O
R1
[Rh(CO)2acac],
base, CO/H2
R1
– o-DPPBA
R2
R2
(o-DPPB)O
R1
O
R2
Scheme 1 Concept of the synthesis of enals by o-DPPB controlled
branched selective hydroformylation and successive elimination.
Herein we wish to report on a new facile synthesis of 1,1-
disubstituted and trisubstituted enals by a tandem-directed
regioselective hydroformylation/b-elimination process of
readily accessible allylic o-DPPB esters (Scheme 1). In
the course of this tandem reaction the o-DPPB group
serves both, as a catalyst-directing group (CDG) for at-
taining high levels of regiocontrol, and as leaving group in
the subsequent elimination reaction.
The starting allylic o-DPPB esters were readily prepared
by esterification of the ortho-diphenylphosphanylbenzoic
SYNTHESIS 2008, No. 14, pp 2169–2176
Advanced online publication: 18.06.2008
x
x.
x
x
.
2
0
0
8
DOI: 10.1055/s-2008-1067140; Art ID: C00908SS
© Georg Thieme Verlag Stuttgart · New York

2170
A. Bruch et al.
PAPER
acid (o-DPPBA) employing Steglich’s conditions
Table 1 Preparation of Allylic o-DPPB Esters
(Table 1).
o-DPPBA,
DCC, DMAP,
CH2Cl2, r.t.
(o-DPPB)O
R2
From previous investigations on hydroformylation of al-
lylic o-DPPB esters we knew that elimination can occur as
a side reaction.16,17 Thus, we wondered whether the addi-
tion of a base during the course of the hydroformylation
reactions might drive the elimination to completion. In-
deed running the directed hydroformylation reaction un-
der standard conditions [1.8 mol% Rh(CO)2acac, 40 bar
CO/H2 (1:1), 40 to 50 °C, in THF (0.1 M), 24 h] in the
presence of either potassium carbonate, triethyl- or dieth-
ylamine a clean tandem hydroformylation/b-elimination
was observed to furnish the corresponding enals in good
to excellent yields (Table 2, Method A). In the case of the
amine bases, stoichiometric amounts were required to
drive the elimination to completion while catalytic
amounts (0.1 equiv) were sufficient for the heterogeneous
potassium carbonate base (Table 2).
OH
R1
R1
82–99%
R2
Entry
1
o-DPPB ester
Yield (%)a
O(o-DPPB)
98
7
1
O(o-DPPB)
2
3
85
82
i-Pr
2
O(o-DPPB)
Cy
3
In a few cases, an undesired hydrogenation of the alkene
function of the resulting enals was observed (entries 10,
11, and 13). This problem could be circumvented by run-
ning the reaction as a one-pot two-step process (Table 2,
Method B). Thus, hydroformylation was carried out in the
absence of a base. After completion of this reaction, the
corresponding base was added to the reaction mixture,
and elimination was completed by stirring at 50–60 °C.
Both reaction conditions – the tandem process (Method
A) and the one-pot two-step process (Method B) – are
compatible with several functional groups such as esters,
acetals, and silyl ethers. Even alkenyl silanes could be
used as substrates to furnish the interesting formyl-substi-
tuted allylsilane building block 25 (entry 12).
O(o-DPPB)
4
5
89
84
Cy
4
O(o-DPPB)
MeOOC
5
O(o-DPPB)
O(o-DPPB)
MeOOC
6
87
6
7
8
99
89
92
92
Ph
7
All trisubstituted enals (Table 2 entries 1–10) were ob-
tained as pure E-stereoisomers as determined by NOE
contact analysis or in case of known compounds on com-
parison with literature spectroscopic data. This suggests
that the elimination takes place according to the E1CB
mechanism.18
O(o-DPPB)
Ph
8
O(o-DPPB)
9
Ph
A practical aspect of this method is the ease of o-DPPBA
recovery, which is achieved by flash chromatography in
the course of the workup process. Interestingly, when
diethylamine was employed as the base the o-DPPBA
precipitated from THF as the corresponding diethyl-
ammonium salt, which allowed separation and recovery
by filtration.
9
O(o-DPPB)
10
TBDPSO
10
O(o-DPPB)
11
12
96
99
7
In conclusion, we have documented a novel, and practical
synthesis of a,b-unsaturated aldehydes by a tandem hy-
droformylation/b-elimination process of allylic o-DPPB
esters. The o-DPPB group served as an effective control-
ler for regioselectivity of the hydroformylation towards
the desired aldolate isomer and can be eliminated easily
by different standard bases. The reaction is rather general
for the preparation of 1,1-disubstituted and trisubstituted
enals and is compatible with many functional groups. Re-
covery of the o-DPPBA is possible either by chromatog-
raphy or precipitation as the diethylammonium salt. The
mild reaction conditions and good to excellent yields of
11
O(o-DPPB)
SiPh2t-Bu
12
O(o-DPPB)
O
13
95
O
13
a Isolated yield after chromatography.
Synthesis 2008, No. 14, 2169–2176 © Thieme Stuttgart · New York

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Synthesis of Enals via Regioselective Hydroformylation/b-Elimination
2171
Table 2 Results of the Tandem o-DPPB Directed Hydroformylation/b-Elimination of Allylic o-DPPB Esters
Entrya o-DPPB-ester
Methodb Temp (°C) Time (h) Base (equiv)
Enal
Yield (%)c
96
O(o-DPPB)
CHO
1
A
50
31
Et3N (1.1)
7
Me
7
14
1
O(o-DPPB)
CHO
i-Pr
2
A
A
A
A
50
50
40
50
24
24
42
24
K2CO3 (0.1)
K2CO3 (0.1)
HNEt2 (2.0)
K2CO3 (0.1)
67
92
86
78
i-Pr
Me
2
15
O(o-DPPB)
CHO
CHO
Cy
3
Cy
Me
16
3
O(o-DPPB)
Cy
4
Cy
Et
17
MeOOC
4
CHO
CHO
O(o-DPPB)
5
6
MeOOC
Me
Me
5
18
O(o-DPPB)
O(o-DPPB)
MeOOC
MeOOC
A
50
24
Et3N (1.1)
84
Me
19
6
CHO
Ph
7
8
A
A
A
B
50
50
50
50
24
14
24
48
Et3N (1.1)
92
88
92
80
Ph
Me
7
20
Ph
CHO
CHO
O(o-DPPB)
K2CO3 (0.1)
K2CO3 (0.1)
Et3N (5.0)
Ph
Me
8
21
Ph
O(o-DPPB)
9
Ph
Et
9
22
TBDPSO
CHO
O(o-DPPB)
10
TBDPSO
Et
10
23
CHO
O(o-DPPB)
11
12
B
A
40
40
24
24
Et3N (5.0)
Et3N (2.0)
93
84
7
7
11
24
25
CHO
O(o-DPPB)
SiPh2t-Bu
SiPh2t-Bu
CHO
12
O(o-DPPB)
O
O
O
13
B
50
24
Et3N (5.0)
78
O
13
a [Rh(CO)2acac] (1.8 mol%), CO/H2 (40 bar), THF (c = 0.1 M).
26
b Method A: tandem process, base present during hydroformylation; Method B: one-pot process, no base present during hydroformylation, ad-
dition of Et3N (5 equiv) after hydroformylation and stirring at 50–60 °C until complete consumption of aldolate product (TLC control).
c Isolated yield.
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2172
A. Bruch et al.
PAPER
7.08 (m, 8 H, ArH), 7.11 (mc, 1 H, ArH), 7.33–7.41 (m, 4 H, ArH),
8.16 (mc, 1 H, ArH).
enals should make this an attractive and practical alterna-
tive synthetic method for the preparation of this important
class of organic compounds.
13C NMR (101 MHz, C6D6): d = 18.1 (CHCH3Me), 18.2
(CHMeCH3), 32.1 (CHMe2), 80.6 (1-C), 117.9 (3-C), 128.3, 128.6,
128.6, 128.7 (d, JC,P = 6.9 Hz, 4 C), 130.8 (d, JC,P = 2.8 Hz, Ar-C),
131.9, 134.2 (d, JC,P = 20.7 Hz, 2 C, Ar-C), 134.5 (d, JC,P = 20.9 Hz,
2 C, Ar-C), 134.9 (2 C, 2-C und Ar-C), 135.8 (d, JC,P = 20.1 Hz, Ar-
Cq), 139.1 (d, JC,P = 13.2 Hz, Ar-Cq), 139.2 (d, JC,P = 12.8 Hz, Ar-
Cq), 141.3 (d, JC,P = 29.0 Hz, Ar-Cq), 165.8 (d, JC,P = 2.1 Hz,
ArCO2R).
Reactions were performed in flame-dried glassware under argon
(purity >99.998%). The solvents were dried by standard procedures,
distilled, and stored under argon. All temperatures quoted are un-
corrected. 1H and 31C NMR spectra: Bruker Avance 400 or Avance
500 spectrometer with TMS, CHCl3, or C6H6 as internal standards.
31P NMR spectra: Varian Mercury 300 spectrometer with 85%
H3PO4 as external standard. Melting points: Melting point apparatus
by Dr. Tottoli (Büchi). Elemental analyses: Elementar Vario EL ap-
paratus. Flash chromatography: silica gel Si 60, E. Merck AG,
Darmstadt, 40–63 mm. Hydroformylation reactions were performed
in 50 and 100 mL stainless-steel autoclaves equipped with magnetic
stirrers. Gases: CO 3.7, H2 4.3 (1:1, Messer-Griesheim). The fol-
lowing compounds were prepared according to literature proce-
dures: (E)-1-cyclohexylbut-2-en-1-ol,19 1-cyclohexylprop-2-en-1-
ol,20 4-methylpent-1-en-3-ol,21 undec-1-en-3-ol,22 3-hydroxypent-
4-enoic acid methyl ester,23 3-hydroxy-2-methylpent-4-enoic acid
methyl ester,24 5-phenylpent-1-en-3-ol,25 1-phenylbut-3-en-2-ol,26
31P NMR (162 MHz, C6D6): d = –4.5 (s).
Anal. Calcd for C25H25O2P: C, 77.30; H, 6.67. Found: C, 76.98; H,
6.49.
o-Diphenylphosphanylbenzoic Acid 1-Cyclohexylallyl Ester (3)
Mp 80–81 °C.
1H NMR (400 MHz, C6D6): d = 0.75–1.11 (m, 5 H, Cy-H), 1.39 (mc,
1 H, 1¢-H), 1.45–1.70 (m, 5 H, Cy-H), 4.99 (ddd, J = 10.5 Hz,
4
2J = 1.6 Hz, J = 1.2 Hz, 1 H, 3-Hcis), 5.16 (ddd, J = 17.2 Hz,
4
2J = 1.6 Hz, J = 1.2 Hz, 1 H, 3-Htrans), 5.32 (dd, J = J = 6.9 Hz, 1
H, 1-H), 5.62 (ddd, J = 17.3, 10.4, 7.0 Hz, 1 H, 2-H), 6.90–7.08 (m,
8 H, ArH), 7.11 (mc, 1 H, ArH), 7.33–7.41 (m, 4 H, ArH), 8.18 (mc,
1 H, ArH).
13C NMR (101 MHz, C6D6): d = 26.2 (2 C, Cy-C), 26.6 (Cy-C),
28.8 (2 C, Cy-C), 41.7 (1¢-C), 80.2 (1-C), 117.8 (3-C), 128.3, 128.6
(2 C), 128.7 (d, JC,P = 6.9 Hz, 4 C), 130.9 (d, JC,P = 2.9 Hz, Ar-C),
131.9, 134.4 (d, JC,P = 20.7 Hz, 2 C, Ar-C), 134.4 (d, JC,P = 20.8 Hz,
2 C, Ar-C), 134.9, 135.4 (2-C), 135.9 (d, JC,P = 20.3 Hz, Ar-Cq),
139.1 (d, JC,P = 13.3 Hz, Ar-Cq), 139.2 (d, JC,P = 13.1 Hz, Ar-Cq),
141.2 (d, JC,P = 28.7 Hz, Ar-Cq), 165.9 (d, JC,P = 2.4 Hz, Ar-C).
(E)-1-phenylpent-3-en-2-ol,27
(E)-1-(tert-butyldiphenylsilyl-
oxy)pent-3-en-2-ol,28 (E)-undec-2-en-1-ol,29 (E)-3-(tert-butyl-
diphenylsilyl)prop-2-en-1-ol,30 3-(2¢,2¢-dimethyl[1¢,3¢]dioxolan-
4¢-yl)prop-2-en-1-ol,31 and ortho-(diphenylphosphanyl)benzoic
acid.32
o-DPPB Esters; General Procedure
o-DPPBA (1.1 equiv), DMAP (0.8 equiv), and DCC (1.1 equiv)
were successively added to a solution of allylic alcohol (1 equiv) in
CH2Cl2 (0.3 M) and the resulting mixture was stirred at r.t. until
TLC showed complete consumption of the starting material. Subse-
quently, the mixture was filtered and concentrated. Flash chroma-
tography (CH2Cl2) afforded the pure o-DPPB ester.
31P NMR (162 MHz, C6D6): d = –4.6 (s).
Anal. Calcd for C28H29O2P: C, 78.48; H, 6.82. Found: C, 78.09; H,
6.80.
o-Diphenylphosphanylbenzoic Acid 1-Octylallyl Ester (1)
Colorless, highly viscous oil.
(E)-o-Diphenylphosphanylbenzoic Acid 1-Cyclohexylbut-2-
enyl Ester (4)
Colorless, highly viscous oil.
1H NMR (400 MHz, C6D6): d = 0.89 (t, J = 7.0 Hz, 3 H, 8¢-H3),
1.08–1.33 (m, 12 H, 2¢-H2, 3¢-H2, 4¢-H2, 5¢-H2, 6¢-H2, 7¢-H2), 1.43
(mc, 1 H, 1¢-HA), 1.57 (mc, 1 H, 1¢-HB), 4.95 (ddd, J = 10.5 Hz,
1H NMR (400 MHz, C6D6): d = 0.78–1.13 (m, 5 H, Cy-H), 1.37–
1.76 (m, 6 H, Cy-H), 1.44 (d, J = 6.5 Hz, 3 H, 4-H3), 5.27–5.36 (m,
2 H, 2-H and 1-H), 5.59 (dq, J = 14.6, 6.4 Hz, 1 H, 3-H), 6.89–7.12
(m, 9 H, ArH), 7.33–7.41 (m, 4 H, ArH), 8.21 (mc, 1 H, ArH).
13C NMR (101 MHz, C6D6): d = 17.8 (4-C), 26.2 (Cy-C), 26.2 (Cy-
C), 26.6 (Cy-C), 28.9 (Cy-C), 29.1 (Cy-C), 41.9 (1¢-C), 80.4 (1-C),
128.3, 128.5, 128.6, 128.6 (2-C), 128.7 (d, JC,P = 6.9 Hz, 4 C), 130.3
(3-C), 130.9 (d, JC,P = 2.9 Hz, Ar-C), 131.8, 134.3 (d, JC,P = 20.7
Hz, 2 C, Ar-C), 134.5 (d, JC,P = 20.8 Hz, 2 C, Ar-C), 134.9, 136.1
(d, JC,P = 20.2 Hz, Ar-Cq), 139.2 (d, JC,P = 12.8 Hz, Ar-Cq), 139.4
(d, JC,P = 12.5 Hz, Ar-Cq), 141.1 (d, JC,P = 28.8 Hz, Ar-Cq), 166.0
(d, JC,P = 2.3 Hz, ArCO2R).
4
2J = 1.4 Hz, J = 1.1 Hz, 1 H, 3-Hcis), 5.16 (ddd, J = 17.2 Hz,
2J = 4J = 1.3 Hz, 1 H, 3-Htrans), 5.50 (td, J = J = 6.6 Hz, 1H, 1-H),
5.65 (ddd, J = 17.2, 10.5, 6.6 Hz, 1 H, 2-H), 6.91 (mc, 1 H, ArH),
6.98 (mc, 1 H, ArH), 7.02–7.08 (m, 6 H, ArH), 7.10 (mc, 1 H, ArH),
7.34–7.41 (m, 4 H, ArH), 8.18 (mc, 1 H, ArH).
13C NMR (101 MHz, C6D6): d = 14.3 (8¢-C), 23.0, 25.5, 29.6, 29.7,
29.8, 32.2, 34.5 (1¢-C), 76.3 (1-C), 116.8 (3-C), 128.3, 128.6 (2 C),
128.7 (d, JC,P = 7.0 Hz, 4 C), 130.9 (d, JC,P = 2.9 Hz, Ar-C), 131.9,
134.4 (d, JC,P = 20.7 Hz, 2 C, Ar-C), 134.4 (d, JC,P = 20.8 Hz, 2 C,
Ar-C), 134.9, 136.0 (d, JC,P = 20.5 Hz, Ar-Cq), 136.9 (2-C), 139.1
(d, JC,P = 13.0 Hz, Ar-Cq), 139.2 (d, JC,P = 12.9 Hz, Ar-Cq), 141.0
(d, JC,P = 28.7 Hz, Ar-Cq), 166.0 (d, JC,P = 2.1 Hz, ArCO2R).
31P NMR (162 MHz, C6D6): d = –4.5 (s).
31P NMR (162 MHz, C6D6): d = –4.6 (s).
Anal. Calcd for C29H31O2P: C, 78.71; H, 7.06. Found: C, 78.54; H,
7.09.
Anal. Calcd for C30H35O2P: C, 78.57; H, 7.69. Found: C, 78.45; H,
7.64.
o-Diphenylphosphanylbenzoic Acid 1-Methoxycarbonyl-
methylallyl Ester (5)
Mp 98–99 °C.
o-Diphenylphosphanylbenzoic Acid 1-Isopropylallyl Ester (2)
Mp 60–62 °C.
1H NMR (400 MHz, C6D6): d = 0.75 (d, J = 6.8 Hz, 3 H,
CHCH3Me), 0.79 (d, J = 6.8 Hz, 3 H, CHMeCH3), 1.72 (d sept,
1H NMR (400 MHz, C6D6): d = 2.49 AB-Signal: 2.38 (A-Teil, dd,
2
2J = 15.7, J = 6.1 Hz, 1 H, 1¢-HA), 2.66 (B-Teil, dd, J = 15.7,
J = 7.5 Hz, 1 H, 1¢-HB), 3.34 (s, 3 H, OCH3), 4.99 (dd, J = 10.5,
2
J = 6.7 Hz, 1 H, CHMe2), 4.96 (ddd, J = 10.5 Hz, J = 1.6 Hz,
4
4J = 1.2 Hz, 1 H, 3-Hcis), 5.24 (dd, J = 17.2, J = 1.2 Hz, 1 H, 3-
4J = 1.1 Hz, 1 H, 3-Hcis), 5.13 (ddd, J = 17.2 Hz, J = 1.6 Hz,
2
Htrans), 5.74 (ddd, J = 17.2, 10.6, 6.3 Hz, 1 H, 2-H), 5.78 (ddddd,
J = J = J = 6.6 Hz, 4J = 4J = 1.2 Hz, 1 H, 2-H), 6.98–7.21 (m, 9 H,
ArH), 7.42–7.49 (m, 4 H, ArH), 8.23 (mc, 1 H, ArH).
4J = 1.2 Hz, 1 H, 3-Htrans), 5.28 (dddd, J = J = 6.5 Hz, 4J = 4J = 1.1
Hz, 1 H, 1-H), 5.57 (ddd, J = 17.3, 10.5, 6.8 Hz, 1 H, 2-H), 6.90–
Synthesis 2008, No. 14, 2169–2176 © Thieme Stuttgart · New York

PAPER
Synthesis of Enals via Regioselective Hydroformylation/b-Elimination
2173
13C NMR (101 MHz, C6D6): d = 39.1 (1¢-C), 51.2 (OCH3), 72.1 (1-
C), 117.5 (3-C), 128.4, 128.6, 128.7, 128.7 (d, JC,P = 7.0 Hz, 4 C),
131.1 (d, JC,P = 3.0 Hz, Ar-C), 132.0, 134.3 (d, JC,P = 20.7 Hz, 2 C,
Ar-C), 134.4 (d, JC,P = 20.8 Hz, 2 C, Ar-C), 134.8, 135.2 (2-C),
135.5 (d, JC,P = 20.8 Hz, Ar-Cq), 138.9 (d, JC,P = 12.7 Hz, Ar-Cq),
139.0 (d, JC,P = 12.8 Hz, Ar-Cq), 141.0 (d, JC,P = 28.7 Hz, Ar-Cq),
165.6 (d, JC,P = 1.9 Hz, ArCO2R), 169.6 (2¢-C).
Anal. Calcd for C30H27O2P: C, 79.98; H, 6.04. Found: C, 79.93; H,
6.14.
o-Diphenylphosphanylbenzoic Acid 1-Benzylallyl Ester (8)
Mp 150–151 °C (MeOH).
1H NMR (300 MHz, CDCl3): d = 2.81 (dd, J = 13.6, 7.0 Hz, 1 H, 1¢-
HA), 2.94 (dd, J = 13.8, 6.5 Hz, 1 H, 1¢-HB), 5.06 (dt, J = 10.6, 1.0
Hz, 1 H, 3-HA), 5.12 (dt, J = 17.3, 1.2 Hz, 1 H, 3-HB), 5.56 (br dd,
J = 13.2, 6.5 Hz, 1 H, 1-H), 6.91 (mc, 1 H, ArH), 7.10–7.41 (m, 17
H, ArH), 8.05 (mc, 1 H, ArH).
31P NMR (121 MHz, C6D6): d = –4.7 (s).
Anal. Calcd for C25H23O4P: C, 71.76; H, 5.54. Found: C, 71.57; H,
5.62.
13C NMR (101 MHz, C6D6): d = 40.7 (C-1¢), 76.2 (C-1), 117.4 (C-
3), 126.5 (Ar-C), 128.2 (Ar-C), 128.3 (2 C, Ar-C), 128.5 (d,
JC,P = 7.3 Hz, 4 C, Ar-C), 128.6 (2 C, Ar-C), 128.7 (2 C, Ar-C),
129.7 (C-2), 130.6 (Ar-C), 131.9 (Ar-C), 133.9 (d, 2 C, JC,P = 20.6
Hz, Ar-C), 134.2 (d, JC,P = 21.3 Hz, 2 C, Ar-C), 134.4 (Ar-C), 134.8
(d, JC,P = 7.3 Hz, Ar-C), 136.9 (Ar-C), 138.1 (d, JC,P = 11.6 Hz, 2 C,
Ar-C), 140.5 (d, JC,P = 27.6 Hz, Ar-C), 165.9 (ArCO2R).
o-Diphenylphosphanylbenzoic Acid 1-(1-Methoxycarbonyleth-
yl)allyl Ester (6)
Colorless, highly viscous oil.
1H NMR (400 MHz, C6D6): d = [0.97 (d, J = 7.2 Hz, 3 H, 2¢-H3)],
1.07 (d, J = 7.1 Hz, 3 H, 2¢-H3), 2.62 (td, J = 7.1, 5.9 Hz, 1 H, 1¢-H),
[2.69 (td, J = J = 7.2 Hz, 1 H, 1¢-H)], 3.26 (s, 3 H, CO2CH3), [3.27
(s, 3 H, CO2CH3)], 4.93 (ddd, J = 10.5 Hz, 2J = 4J = 1.2 Hz, 1 H, 3-
Hcis), [4.94 (ddd, J = 10.5 Hz, 2J = 1.4 Hz, 4J = 1.0 Hz, 1 H, 3-Hcis)],
5.11 (ddd, J = 17.2 Hz, 2J = 4J = 1.3 Hz, 1 H, 3-Htrans), [5.15 (ddd,
J = 17.2 Hz, 2J = 4J = 1.3 Hz, 1 H, 3-Htrans)], [5.53 (ddd,
J = 17.4, 10.3, 6.8 Hz, 1 H, 2-H)], 5.67 (ddd, J = 17.2, 10.4, 6.5 Hz,
1 H, 2-H), 5.77–5.84 (m, 1 H, 1-H)*, 6.91 (mc, 1 H, ArH)*, 6.97
(mc, 1 H, ArH)*, 7.01–7.07* (m, 6 H, ArH), 7.10 (mc, 1 H, ArH)*,
7.32–7.39 (m, 4 H, ArH)*, 8.15* (mc, 1 H, ArH). [ ] = diastereomer;
* overlayed signals of both diastereomers.
13C NMR (101 MHz, C6D6): d = 12.5 (2¢-C), [12.7 (2¢-C)], 43.7 (1¢-
C), [43.9 (1¢-C)], 51.3 (CO2CH3), 76.3 (1-C), [76.6 (1-C)], 118.4 (3-
C), [119.3 (3-C)], 128.4*, 128.6*, 128.7 (2 C)*, 128.7*, 128.7*,
128.8*, 130.9 (d, JC,P = 2.8 Hz, Ar-C), [131.0 (d, JC,P = 2.7 Hz, Ar-
C)], 132.0, [132.1], 133.5 (2-C), [134.1 (2-C)], 134.3 (d, JC,P = 20.7
Hz, 2 C, Ar-C)*, 134.5 (d, JC,P = 20.9 Hz, 2 C, Ar-C)*, [134.9],
134.9, 135.2 (d, JC,P = 20.1 Hz, Ar-Cq), [135.3 (d, JC,P = 20.2 Hz,
Ar-Cq)], [138.9 (d, JC,P = 12.5 Hz, 2 C, Ar-Cq)], 139.0 (d, JC,P = 13.3
Hz, Ar-Cq), 139.0 (d, JC,P = 12.9 Hz, Ar-Cq), 141.4 (d, JC,P = 29.2
Hz, Ar-Cq), [141.5 (d, JC,P = 29.1 Hz, Ar-Cq)], 165.3 (d, JC,P = 2.2
Hz, ArCO2R), [165.3 (d, JC,P = 2.2 Hz, ArCO2R)], 173.1 (CO2Me)*.
[ ] = diastereomer; * overlayed signals of both diastereomers.
31P NMR (121 MHz, C6D6): d = –4.6 (s).
Anal. Calcd for C29H25O2P: C, 79.80; H, 5.77. Found: C, 79.60; H,
5.79.
(E)-o-Diphenylphosphanylbenzoic Acid 1-Benzylbut-2-enyl
Ester (9)
Mp 91–92 °C (MeOH).
1H NMR (300 MHz, CDCl3): d = 1.58 (td, J = 6.5, 1.1 Hz, 3 H, 5-
H3), 2.79 (dd, J = 13.6, 6.7 Hz, 1 H, 1-Ha), 2.82 (dd, 13.7, 6.5 Hz, 1
H, 1-Hb), 5.32 (ddq, J = 15.4, 7.0, 1.2 Hz, 1 H, 3-H), 5.52 (mc, 1 H,
2-H), 5.58 (dqd, J = 15.4, 6.5, 0.8 Hz, 1 H, 4-H), 6.90 (mc, 1 H,
ArH), 7.15–7.39 (m, 12 H, ArH), 7.98 (mc, 1 H, ArH).
13C NMR (101 MHz, CDCl3): d = 17.8 (C-5), 41.0 (C-1), 76.4 (C-
2), 126.4 (Ar-C), 128.19 (2 C, Ar-C), 128.23 (Ar-C), 128.46 (Ar-C),
128.5 (d, JC,P = 7.2 Hz, 4 C), 128.53 (C-2), 128.6 (2 C, Ar-C), 129.7
(C-3), 129.7 (Ar-C), 130.6 (d, JC,P = 0.9 Hz, Ar-C), 131.8 (Ar-C),
134.0 (d, JC,P = 20.6 Hz, 2 C, Ar-C), 134.1 (d, JC,P = 20.5 Hz, 2 C,
Ar-C), 134.3 (Ar-C), 134.9 (d, JC,P = 18.7 Hz, Ar-C), 137.2 (Ar-C),
138.23 (d, JC,P = 11.7 Hz, Ar-C), 138.26 (d, JC,P = 11. 5 Hz, Ar-C),
140.3 (d, JC,P = 26.9 Hz, Ar-C), 166.0 (d, JC,P = 2.4 Hz, (ArCO2R).
31P NMR (121 MHz, CDCl3): d = –4.51 (s).
31P NMR (162 MHz, C6D6): d = –4.64 (s), [–4.60 (s)]. [ ] = diaste-
reomer.
Anal. Calcd for C30H27O2P: C, 79.98; H, 6.04. Found: C, 79.93; H,
6.14.
Anal. Calcd for C26H25O4P: C, 72.21; H, 5.83. Found: C, 71.88; H,
5.76.
(E)-o-Diphenylphosphanylbenzoic Acid 1-(tert-Butyldiphenyl-
silyloxymethyl)but-2-enyl Ester (10)
Colorless, highly viscous oil.
o-Diphenylphosphanylbenzoic Acid 1-Phenethylallyl Ester (7)
Colorless, highly viscous oil.
1H NMR (400 MHz, CDCl3): d = 0.99 (s, 9 H, t-C4H9), 1.61 (dd,
3J = 6.4 Hz, 4J = 1.4 Hz, 3 H, 5-H), 3.62 (dd, 2J = 10.7 Hz, 3J = 6.3
Hz, 1 H, 1-HA), 3.59 (dd, 2J = 10.7 Hz, 3J = 4.8 Hz, 1 H, 1-HB), 5.53
(ddq, 3J = 15.3 Hz, 3J = 7.2 Hz, 4J = 1.4 Hz, 1 H, 3-H), 5.48 (mc, 1
1H NMR (400 MHz, C6D6): d = 1.76 AB spin system: 1.68 (A part,
dddd, 2J = 13.8 Hz, J = 10.2 Hz, J = 6.3 Hz, J = 5.6 Hz, 1 H, 1¢-HA),
1.85 (B part, dddd, 2J = 13.7 Hz, J = 9.9 Hz, J = 7.6 Hz, J = 5.8 Hz,
2
1 H, 1¢-HB), 2.48 AB-Signal: 2.44 (A-Teil, ddd, J = 13.9 Hz,
3
3
H, 2-H), 5.67 (dqd, J = 15.3 Hz, J = 8.6 Hz, 4J = 0.5 Hz, 1 H, 4-
H), 6.89 (m, 1 H, ArH), 7.17–7.43 (m, 18 H, ArH), 7.63 (m, 4 H,
ArH), 8.08 (m, 1 H, ArH).
J = 9.9 Hz, J = 6.3 Hz, 1 H, 2¢-HA), 2.52 (B-Teil, ddd, 2J = 13.9 Hz,
J = 10.1 Hz, J = 5.6 Hz, 1 H, 2¢-HB), 4.91 (ddd, J = 10.4 Hz,
4
4J = 4J = 1.2 Hz, 1 H, 3-Hcis), 5.10 (ddd, J = 17.1 Hz, J = 2J = 1.2
Hz, 1 H, 3-Htrans), 5.50 (ddddd, J = J = J = 6.6 Hz, 4J = 4J = 1.1 Hz,
1 H, 1-H), 5.58 (ddd, J = 17.0, 10.5, 6.5 Hz, 1 H, 2-H), 6.89–7.14
(m, 14 H, ArH), 7.33–7.40 (m, 4 H, ArH), 8.14 (mc, 1 H, ArH).
13C NMR (101 MHz, CDCl3): d = 17.9 (5-C), 19.2 (CMe3), 26.7
[C(CH3)], 65.4 (1-C), 75.9 (2-C), 126. 3 (3-C), 127.6 (2 C), 128.1,
128.3 (d, J = 7.3 Hz, 2 C), 128.4 (d, J = 7.3 Hz, 2 C), 128.5 (2 C),
129.6 (4 C), 130.5 (C-4), 130.72 (d, J = 2.7 Hz, Ar-C), 131.75,
131.8 (2 Ar-Cq), 133.89 (d, J = 20.6 Hz, 2 C), 133.92 (d, J = 20.6
Hz, 2 C), 134.0, 134.3 (d, J = 19.4 Hz, Ar-Cq), 135.7 (2 C), 134.8 (2
C), 135.6 (d, JC,P = 11.8 Hz, 2 Ar-Cq), 138.2 (d, JC,P = 27.2 Hz, 2
Cq), 165.8 (d, J = 7.3 Hz, ArCO2R).
13C NMR (101 MHz, C6D6): d = 31.8 (2¢-C), 36.2 (1¢-C), 75.7 (1-C),
117.0 (3-C), 126.1, 128.3, 128.6 (2 C), 128.6, 128.7 (2 C), 128.7,
128.7 (3 C), 128.8, 131.0 (d, JC,P = 2.9 Hz, Ar-C), 131.9, 134.3 (d,
JC,P = 20.9 Hz, 2 C, Ar-C), 134.5 (d, JC,P = 20.9 Hz, 2 C, Ar-C),
134.9, 135.8 (d, JC,P = 20.5 Hz, Ar-Cq), 136.6 (2-C), 139.0 (d,
JC,P = 13.0 Hz, Ar-Cq), 139.1 (d, JC,P = 12.6 Hz, Ar-Cq), 141.0 (d,
JC,P = 28.6 Hz, Ar-Cq), 141.7, 166.0 (d, JC,P = 2.9 Hz, ArCO2R).
31P NMR (121 MHz, CDCl3): d = –4.8 (s).
Anal. Calcd for C40H41O3PSi: C, 76.40; H, 6.57. Found: C, 76.28;
H, 6.63.
31P NMR (162 MHz, C6D6): d = –4.6 (s).
Synthesis 2008, No. 14, 2169–2176 © Thieme Stuttgart · New York

2174
A. Bruch et al.
PAPER
(E)-o-Diphenylphosphanylbenzoic Acid Undec-2-enyl Ester
(11)
Colorless, highly viscous oil.
(E)-2,4-Dimethylpent-2-enal (15)
1H NMR (400 MHz, CDCl3): d = 1.09 [d, J = 6.7 Hz, 6 H,
CH(CH3)2], 1.75 (s, 3 H, 2-CH3), 2.83 (d sept, J = 9.6, 6.7 Hz, 1 H,
4-H), 6.28 (dd, J = 9.6, 1.4 Hz, 1 H, 3-H), 9.38 (s, 1 H, 1-H).
1H NMR (400 MHz, C6D6): d = 0.90 (t, J = 7.0 Hz, 3 H, 11-H3),
1.12–1.43 (m, 12 H, 5-H2, 6-H2, 7-H2, 8-H2, 9-H2, 10-H2), 1.83 (td,
J = J = 6.6 Hz, 2 H, 4-H2), 4.52 (dd, J = 6.2 Hz, 4J = 0.9 Hz, 2 H, 1-
H2), 5.41 (dtt, J = 15.4 Hz, J = 6.2 Hz, 4J = 1.1 Hz, 1 H, 2-H*), 5.51
(dtt, J = 15.4 Hz, J = 6.4 Hz, 4J = 0.9 Hz, 1 H, 3-H*), 6.91 (mc, 1 H,
ArH), 6.96 (mc, 1 H, ArH), 7.03–7.09 (m, 6 H, ArH), 7.11 (mc, 1 H,
ArH), 7.38–7.44 (m, 4 H, ArH), 8.11 (mc, 1 H, ArH). * Signal as-
signment interchangeable.
13C NMR (101 MHz, C6D6): d = 14.3, 23.0, 29.2, 29.5, 29.6, 29.8,
32.2, 32.5, 65.9, 124.3, 128.3, 128.6 (2 C), 128.7 (d, JC,P = 7.0 Hz,
4 C), 130.9 (d, JC,P = 2.7 Hz, Ar-C), 131.9, 134.4 (d, JC,P = 20.8 Hz,
4 C, Ar-C), 134.7, 135.6 (d, JC,P = 19.9 Hz, Ar-Cq), 136.3, 139.1 (d,
JC,P = 12.8 Hz, 2 C, Ar-Cq), 141.3 (d, JC,P = 28.8 Hz, Ar-Cq), 166.5
(d, JC,P = 2.1 Hz, ArCO2R).
13C NMR (100.1 MHz, CDCl3): d = 9.2 (2-CH3), 21.8 [2 C,
CH(CH3)2], 28.2 (C-4), 137.1 (C-2), 161.2 (C-3), 195.7 (C-1).
Analytical and spectroscopic data correspond to those reported pre-
viously.33
(E)-3-Cyclohexyl-2-methylpropenal (16)
1H NMR (400 MHz, CDCl3): d = 1.20–1.40 (m, 6 H, Cyclohexyl),
1.66–1.82 (m, 5 H, Cyclohexyl), 1.75 (d, J = 1.4 Hz, 3 H, 2-CH3),
2.56 (mc, 1 H, 4-H), 6.29 (dq, J = 9.5, 1.4 Hz, 1 H, 3-H), 9.37 (s, 1
H, 1-H).
13C NMR (100.1 MHz, CDCl3): d = 9.3 (2-CH3), 25.5 (2 C, C-1¢),
25.9 (C-3¢), 31.8 (2 C, C-2¢), 38.0 (C-4), 137.5 (C-2), 159.7 (C-3),
195.8 (C-1).
31P NMR (121 MHz, C6D6): d = –3.9 (s).
Analytical and spectroscopic data correspond to those reported pre-
viously.34
Anal. Calcd for C30H35O2P: C, 78.57; H, 7.69. Found: C, 78.63; H,
7.60.
3-Cyclohexyl-2-ethylpropenal (17)
(E)-o-Diphenylphosphanylbenzoic acid 3-(tert-butyldiphenyl-
silyl)allyl Ester (12) and (E)-o-Diphenylphosphanylbenzoic
Acid 3-(2¢,2¢-dimethyl[1¢,3¢]dioxolan-4¢-yl)allyl Ester (13)
For preparation and analytical data, see ref.16
1H NMR (500 MHz, CDCl3): d = 0.98 (t, J = 7.6 Hz, 3 H, 2¢-H3),
1.16–1.40 (m, 5 H, Cy-H), 1.65–1.81 (m, 5 H, Cy-H), 2.25 (q,
J = 7.5 Hz, 2 H, 1¢-H2), 2.52 (mc, 1 H, 1¢¢-H), 6.22 (d, J = 9.9 Hz, 1
H, 3-H), 9.33 (s, 1 H, 1-H).
13C NMR (126 MHz, CDCl3): d = 14.1 (2¢-C), 17.6 (1¢-C), 25.5 (2
C, Cy-C), 25.8 (Cy-C), 32.2 (2 C, Cy-C), 38.0 (1¢¢-C), 143.4 (2-C),
159.7 (3-C), 195.7 (1-C).
Enals from Allylic o-DPPB Esters; General Procedure
Method A: o-DPPB ester (1 equiv) was dissolved in THF (0.1 M)
and [Rh(CO)2acac] (1.8 mol%) and base were added. The mixture
was stirred for 5 min and then transferred by syringe into an oven-
dried stainless-steel tube autoclave (in the case of K2CO3, the base
was loaded into the autoclave prior to the transfer of the substrate/
catalyst solution). The argon in the autoclave was removed by a
pressurizing/depressurizing cycle (3 × 5 bar CO/H2) and finally the
autoclave was pressurized with 40 bar CO/H2 (1:1). The mixture
was stirred at elevated temperature for the indicated time. After re-
leasing the pressure, the solvent was removed in vacuo and the enal
was isolated by flash chromatography [petroleum ether (bp 40–60
°C)–Et2O] as colorless oils.
Anal. Calcd for C11H18O: C, 79.46; H, 10.91. Found: C, 79.10; H,
10.60.
(E)-4-Methyl-5-oxopent-3-enoic Acid Methyl Ester (18)
1H NMR (500 MHz, CDCl3): d = 1.76 (dt, 4J = 5J = 1.1 Hz, 3 H, 4-
CH3), 3.40 (dq, J = 7.0 Hz, 5J = 0.9 Hz, 2 H, 2-H2), 3.75 (s, OCH3),
6.69 (tq, J = 7.0 Hz, 4J = 1.4 Hz, 1 H, 3-H), 9.47 (s, 1 H, 5-H).
13C NMR (126 MHz, CDCl3): d = 9.6 (2-CH3), 34.2 (4-C), 52.5
(OCH3), 141.5 (2-C), 144.1 (3-C), 170.4 (5-C), 194.6 (1-C).
Analytical and spectroscopic data correspond to those reported pre-
viously.35
Method B: o-DPPB ester (1 equiv) was dissolved in THF (0.1 M)
and [Rh(CO)2acac] (1.8 mol%) was added. The mixture was stirred
for 5 min and then transferred by syringe into an oven-dried stain-
less-steel tube autoclave. The argon in the autoclave was removed
by a pressurizing/depressurizing cycle (3 × 5 bar CO/H2) and finally
the autoclave was pressurized with 40 bar CO/H2 (1:1). The mixture
was stirred at elevated temperature for the indicated period of time.
After pressure release, the solvent was removed in vacuo, CH2Cl2
(3 mL) and Et3N (5 equiv) were added and the mixture was stirred
at 50–60 °C. After TLC control indicated quantitative elimination
(2–6 h), the solvents were removed in vacuo and the enal was iso-
lated by flash chromatography [petroleum ether (bp 40–60 °C)–
Et2O] as colorless oils.
(E)-2,4-Dimethyl-5-oxopent-3-enoic Acid Methyl Ester (19)
1H NMR (500 MHz, CDCl3): d = 1.36 (d, J = 7.0 Hz, 3 H, 2-CH3),
1.78 (d, 4J = 1.4 Hz, 3 H, 4-CH3), 3.64 (dq, J = 9.6, 7.1 Hz, 1 H, 2-
H), 3.72 (s, 3 H, CO2CH3), 6.51 (dq, J = 9.6 Hz, 4J = 1.4 Hz, 1 H, 3-
H), 9.43 (s, 1 H, 1-H).
13C NMR (126 MHz, CDCl3): d = 9.3 (4-CH3), 17.2 (2-CH3), 39.5
(2-C), 52.4 (CO2CH3), 139.9 (4-C)*, 150.8 (3-C), 173.5 (CO2Me)*,
194.9 (1-C). * Signal assignment interchangeable.
Anal. Calcd for C8H12O3: C, 61.52; H, 7.74. Found: C, 61.45; H,
7.60.
(E)-2-Methyl-5-phenylpent-2-enal (20)
(E)-2-Methylundec-2-enal (14)
1H NMR (500 MHz, CDCl3): d = 1.69 (d, 4J = 1.0 Hz, 3 H, 2-CH3),
2.69 (td, J = J = 7.5 Hz, 2 H, 4-H2), 2.83 (t, J = 7.6 Hz, 2 H, 5-H2),
1H NMR (500 MHz, CDCl3): d = 0.88 (t, J = 7.0 Hz, 3 H, 11-H3),
1.22–1.37 (m, 10 H, 6-H2, 7-H2, 8-H2, 9-H2, 10-H2), 1.49 (tt,
J = J = 7.4 Hz, 2 H, 5-H2), 1.74 (dt, 4J = 5J = 1.0 Hz, 3 H, 2-CH3),
2.33 (tdq, J = J = 7.5 Hz, 5J = 0.8 Hz, 2 H, 4-H2), 6.49 (tq, J = 7.4
Hz, 4J = 1.4 Hz, 1 H, 3-H), 9.39 (s, 1 H, 1-H).
4
6.52 (tq, J = 7.3 Hz, J = 1.3 Hz, 1 H, 3-H), 7.18–7.25 (m, 3 H,
ArH), 7.28–7.33 (m, 2 H, ArH), 9.39 (s, 1 H, 1-H).
13C NMR (126 MHz, CDCl3): d = 9.2 (2-CH3), 30.7 (4-C), 34.4 (5-
C), 126.3 (Ar-C), 128.4 (2 C, Ar-C), 128.6 (2C, Ar-C), 139.9 (Ar-
C)*, 140.6 (2-C)*, 153.2 (3-C), 195.2 (1-C). * Signal assignment in-
terchangeable.
13C NMR (126 MHz, CDCl3): d = 9.3 (2-CH3), 14.2 (11-C), 22.7,
28.5, 29.1, 29.3, 29.4, 29.5, 31.9, 139.4 (2-C), 155.2 (3-C), 195.5
(1-C).
Analytical and spectroscopic data correspond to those reported pre-
viously.36
Anal. Calcd for C12H22O: C, 79.06; H, 12.16. Found: C, 78.79; H,
11.96.
Synthesis 2008, No. 14, 2169–2176 © Thieme Stuttgart · New York

PAPER
Synthesis of Enals via Regioselective Hydroformylation/b-Elimination
2175
(E)-2-Methyl-4-phenylbut-2-enal (21)
13C NMR (101 MHz, CDCl3): d = 25.7 (2¢-CH3A), 27.1 (2¢-CH3B),
32.3 (1¢¢-C), 69.2 (5¢-C), 73.9 (4¢-C), 109.3 (2¢-C), 136.7 (3-C),
146.1 (2-C), 194.3 (1-C).
4
1H NMR (500 MHz, CDCl3): d = 1.88 (d, J = 1.0 Hz, 3 H, CH3),
3.70 (d, J = 7.4 Hz, 2 H, 4-H2), 6.65 (tq, J = 7.4 Hz, 4J = 1.4 Hz, 1
H, 3-H), 7.18–7.22 (m, 2 H, ArH), 7.24–7.28 (m, 1 H, ArH), 7.31–
7.36 (m, 2 H, ArH), 9.44 (s, 1 H, 1-H).
Anal. Calcd for C9H14O3: C, 63.51; H, 8.29. Found: C, 63.52; H,
8.34.
13C NMR (126 MHz, CDCl3): d = 9.5 (2-CH3), 35.3 (4-C), 126.8
(Ar-C), 128.6 (2 C, Ar-C), 128.9 (2 C, Ar-C), 138.3 (Ar-C), 139.7
(2-C), 152.2 (3-C), 195.2 (1-C).
Acknowledgment
Anal. Calcd for C11H12O: C, 82.46; H, 7.55. Found: C, 82.21; H,
7.45.
This work was supported by the Fonds der Chemischen Industrie,
the DFG Int. GRK 1038 (‘Catalysts and Catalytic Reactions for
Organic Synthesis’), the Alfried Krupp Award for young univer-
sity teachers of the Krupp foundation (to B.B.). We thank Wacker
Chemie AG and Chemtura Organometallics GmbH for donation of
chemicals.
(E)-2-Ethyl-4-phenylbut-2-enal (22)
1H NMR (400 MHz, CDCl3): d = 1.87 (dd, J = 1.3, 0.9 Hz, 3 H, 2-
CH3), 3.69 (d, J = 7.6 Hz, 2 H, 4-H2), 6.63 (tq, J = 7.3, 1.3 Hz, 1 H,
3-H), 7.18–7.35 (m, 5 H, ArH), 9.43 (s, 1 H, 1-H).
13C NMR (100.1 MHz, CDCl3): d = 9.4 (2-CH3), 35.2 (C-4), 126.8
(Ar-C), 128.5 (2 C, Ar-C), 128.9 (2 C, Ar-C), 138.2 (Ar-C) 139.6
(C-2), 152.2 (C-3), 195.1 (C-1).
References
(1) Wichard, T.; Göbel, C.; Feussner, I.; Pohnert, G. Angew.
Chem. Int. Ed. 2005, 44, 158; Angew. Chem. 2005, 116, 161.
(2) Rowe, D. J. Perf. Flav. 2000, 25, 1.
Analytical and spectroscopic data correspond to those reported pre-
viously.34
(3) Mackie, P. R.; Foster, C. E. In Comprehensive Organic
Functional Group Transformations II, Vol. 3; Katritzky, A.
R.; Taylor, R. J. K., Eds.; Pergamon: Oxford, 2005, 59–97.
(4) Escher, I.; Glorius, F. In Science of Synthesis, Vol. 25;
Brückner, R., Ed.; Thieme: Stuttgart, 2007, 733–777.
(5) (a) Olah, G. A.; Arvanaghi, M. Angew. Chem., Int. Ed. Engl.
1981, 20, 878; Angew. Chem. 1981, 93, 925. (b) For more
examples see ref. 4.
(E)-4-(tert-Butyldiphenylsilyloxy)-2-ethylbut-2-enal (23)
1H NMR (500 MHz, CDCl3): d = 0.82 (t, J = 7.6 Hz, 3 H, 2¢-H3),
1.08 (s, 9 H, t-C4H9), 2.07 (q, J = 7.6 Hz, 2 H, 1¢-H2), 4.54 (d,
J = 5.5 Hz, 2 H, 4-H2), 6.53 (t, J = 5.4 Hz, 1 H, 3-H), 7.37–7.48 (m,
6 H, ArH), 7.65–7.71 (m, 4 H, ArH), 9.38 (s, 1 H, 1-H).
13C NMR (126 MHz, CDCl3): d = 13.1, 17.6, 19.2, 26.8 [3 C,
C(CH3)3], 61.0, 127.9 (4 C, Ar-C), 130.0 (2 C, Ar-C), 133.1 (2 C,
Ar-C), 135.6 (4 C, Ar-C), 143.9, 152.3, 194.5.
(6) Crimmins, M. T.; King, B. W. J. Am. Chem. Soc. 1998, 120,
9084.
(7) (a) Wittig, G.; Reiff, H. Angew. Chem., Int. Ed. Engl. 1968,
7, 7; Angew. Chem. 1968, 80, 8. (b) Corey, E. J.; Enders, D.;
Bock, M. G. Tetrahedron Lett. 1976, 17, 7.
Anal. Calcd for C22H28O2Si: C, 74.95; H, 8.01. Found: C, 74.71; H,
7.94.
(8) Duhamel, L.; Gralak, J.; Bouyanzer, A. Tetrahedron Lett.
2-Nonylpropenal (24)
1H NMR (400 MHz, CDCl3): d = 0.88 (t, J = 6.9 Hz, 3 H, 9¢-H3),
1.22–1.36 (m, 12 H, 8¢-H2, 7¢-H2, 6¢-H2, 5¢-H2, 4¢-H2, 3¢-H2), 1.44
(tt, J = 7.3, 7.3 Hz, 2 H, 2¢-H2), 2.23 (t, J = 7.8 Hz, 2 H, 1¢-H2), 5.98
(s, 1 H, 3-HA), 6.24 (s, 1 H, 3-HB), 9.54 (s, 1 H, 1-H).
1993, 34, 7745.
(9) Wollenberg, R. H.; Albizati, K. F.; Peries, R. J. Am. Chem.
Soc. 1977, 99, 7365.
(10) Trippet, S.; Walker, D. M. J. Chem. Soc. 1961, 1266.
(11) Applications: (a) Zhou, G.; Hu, Q.-Y.; Corey, E. J. Org. Lett.
2003, 5, 3979. (b) Nagamitsu, T.; Takano, D.; Fukuda, T.;
Otoguro, K.; Kuwajima, I.; Harigaya, Y.; Omura, S. Org.
Lett. 2004, 6, 1865.
(12) Cresp, T. M.; Sargent, M. V.; Vogel, P. J. Chem. Soc.,
Perkin Trans. 1 1974, 37.
(13) (a) Nagata, W.; Hayase, Y. J. Chem. Soc. C 1969, 460.
(b) Nagata, W.; Hayase, Y. Tetrahedron Lett. 1968, 4359.
(14) Johnson, J. R.; Cuny, G. D.; Buchwald, S. L. Angew. Chem.,
Int. Ed. Engl. 1995, 16, 1760.
(15) (a) Breit, B. In Topics in Organometallic Chemistry,
‘Directed Metallation’, Vol. 24; Chatani, N., Ed.; Springer:
Berlin, 2007, 145–168; and references cited therein.
(b) Breit, B. Acc. Chem. Res. 2003, 36, 264; and references
cited therein.
(16) Breit, B.; Grünanger, C. U.; Abillard, O. Eur. J. Org. Chem.
2007, 2497.
(17) Breit, B. Acc. Chem. Res. 2003, 36, 264.
(18) For an E2 process, the formation of the Z-configured enals
from the anti-aldolate hydroformylation products is
expected.
13C NMR (126 MHz, CDCl3): d = 14.2, 22.8, 27.9, 27.9, 29.4 (2 C),
29.5, 29.6, 32.0, 133.9, 150.6, 194.9.
Analytical and spectroscopic data correspond to those reported pre-
viously.37
2-[(tert-Butyldiphenylsilyl)methyl]propenal (25)
1H NMR (400 MHz, CDCl3): d = 1.07 (s, 9 H, t-C4H9), 2.37 (d,
4J = 1.2 Hz, 2 H, 1¢-H2), 5.65 (d, 2J = 0.5 Hz, 1 H, 3-HA), 5.68 (td,
4J = 1.2 Hz, 2J = 0.7 Hz, 1 H, 3-HB), 7.32–7.42 (m, 6 H, ArH), 7.57–
7.61 (m, 4 H, ArH), 9.24 (s, 1 H, 1-H).
13C NMR (101 MHz, CDCl3): d = 9.8 (1¢-C), 18.6 (CMe3), 27.8 [3
C, C(CH3)3], 127.6 (4 C, Ar-C), 129.4 (2 C, Ar-C), 133.7 (2-C*),
133.9 (3-C*), 136.4 (4 C, Ar-C), 147.2 (2 C, Ar-C*), 194.6 (1-C). *
Signal assignment interchangeable.
Anal. Calcd for C20H24OSi: C, 77.87; H, 7.84. Found: C, 77.84; H,
7.77.
(4¢S)-2-(2¢,2¢-Dimethyl[1¢,3¢]dioxolan-4¢-ylmethyl)propenal (26)
[a]D –101.1 (c 18.8 mg/mL in CHCl3).
1H NMR (400 MHz, CDCl3): d = 1.33 (s, 3 H, 2¢-CH3A), 1.41 (s, 3
H, 2¢-CH3B), 2.52 AB-spin system: 2.48 (A part, dd, 2J = 14.4 Hz,
J = 7.5 Hz, 1 H, 1¢¢-HA), 2.54 (B part, ddd, 2J = 14.4 Hz, J = 5.2 Hz,
4J = 1.2 Hz, 1 H, 1¢¢-HB), 3.56 (dd, 2J = 8.2 Hz, J = 6.7 Hz, 1 H, 5¢-
HA), 4.02 (dd, 2J = 8.2 Hz, J = 6.0 Hz, 1 H, 5¢-HB), 4.24 (mc, 1 H,
(19) Grummit, O.; Splitter, J. J. Am. Chem. Soc. 1952, 74, 3924.
(20) Bergmeier, S. C.; Stanchina, D. M. J. Org. Chem. 1997, 62,
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(21) Denmark, S. E.; Harmata, M. A.; White, K. S. J. Org. Chem.
1987, 52, 4031.
4
4¢-H), 6,12 (s, 1 H, 3-HA), 6.43 (dt, J = 2J* = 1.0 Hz, 1 H, 3-HB),
(22) Ramiandrasod, F.; Descoins, C. Synth. Commun. 1990, 20,
1989.
9.54 (s, 1 H, 1-H). * Not resolved for the coupling partner.
Synthesis 2008, No. 14, 2169–2176 © Thieme Stuttgart · New York

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