Novel chiral bisformamide-promoted asymmetric allylation of benzaldehyde with allyltrichlorosilane

Article abstract of DOI:10.1080/00397911.2010.519841

Novel chiral bisformamides have been prepared from (R,R)-1,2- cyclohexanediamine and utilized as Lewis bases in the asymmetric allylation of benzaldehyde with allyltrichlorosilane. The reaction in the presence of Lewis base 1i gave an 83:17 enantiomeric r

Full text of DOI:10.1080/00397911.2010.519841

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Novel Chiral Bisformamide-Promoted
Asymmetric Allylation of Benzaldehyde
with Allyltrichlorosilane
Kaori Ishimaru a , Kaori Ono a , Yuya Tanimura a & Takakazu Kojima a
a Department of Chemistry, National Defense Academy, Hashirimizu,
Yokosuka, Japan
Accepted author version posted online: 30 Jun 2011.Published
online: 08 Jun 2011.
To cite this article: Kaori Ishimaru , Kaori Ono , Yuya Tanimura & Takakazu Kojima (2011) Novel Chiral
Bisformamide-Promoted Asymmetric Allylation of Benzaldehyde with Allyltrichlorosilane, Synthetic
Communications: An International Journal for Rapid Communication of Synthetic Organic Chemistry,
41:24, 3627-3634, DOI: 10.1080/00397911.2010.519841
To link to this article: http://dx.doi.org/10.1080/00397911.2010.519841
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Synthetic Communications1, 41: 3627–3634, 2011
Copyright # Taylor & Francis Group, LLC
ISSN: 0039-7911 print=1532-2432 online
DOI: 10.1080/00397911.2010.519841
NOVEL CHIRAL BISFORMAMIDE-PROMOTED
ASYMMETRIC ALLYLATION OF BENZALDEHYDE
WITH ALLYLTRICHLOROSILANE
Kaori Ishimaru, Kaori Ono, Yuya Tanimura, and
Takakazu Kojima
Department of Chemistry, National Defense Academy, Hashirimizu,
Yokosuka, Japan
GRAPHICAL ABSTRACT
Abstract Novel chiral bisformamides have been prepared from (R,R)-1,2-cyclohexanediamine
and utilized as Lewis bases in the asymmetric allylation of benzaldehyde with allyltrichloro-
silane. The reaction in the presence of Lewis base 1i gave an 83:17 enantiomeric ratio (R=S)
of the products in 90% isolated yield.
Keywords Aldehyde; allylation; bisformamide; Lewis base
INTRODUCTION
The asymmetric allylation of aldehydes with allylsilanes is one of the most
important carbon–carbon bond-formation reactions in organic synthesis.[1] In parti-
cular, allylation promoted by Lewis bases without the presence of metals has been an
attractive synthetic approach.[2,3] Recently, allylations of aldehydes using chiral
N-oxide,[4] bis-N-oxide,[5] tri-N-oxide,[6] phosphoramide,[7] bisphosphoramide,[8]
phosphine oxide,[9] formamide,[10] diamine,[11] and proline catalysts[12] have been
demonstrated to furnish the products in excellent yields and enantioselectivities. This
is the first report of allylation using chiral C2-symmetric bisformamides to investigate
their Lewis basicity and applications. During the course of our studies, Feng et al.
reported an asymmetric one-pot, three-component Strecker reaction using chiral
bisformamides;[13] however, the catalysts had four chiral centers, and two formyl
Received September 7, 2010.
Address correspondence to Kaori Ishimaru, Department of Chemistry, National Defense
Academy, Hashirimizu 1-10-20, Yokosuka 239-8686, Japan. E-mail: kaoriisi@nda.ac.jp
3627

3628
K. ISHIMARU ET AL.
Scheme 1. Lewis bases la and lb.
and two amide moieties were necessary to control the reactivities and the enantio-
selectivities of the products. In this communication, we describe the preparation of
novel chiral bisformamides and their first application to the asymmetric allylation
reaction.
First, we prepared chiral bisformamides 1a[7e] and 1b from (S,S)-1,2-
diphenylethylenediamine and (R,R)-1,2-cyclohexanediamine, respectively (Scheme 1).
1
The H NMR spectra of the chiral bisformamides show the mixture of rotamers;
see supporting information in Ref. 7e. Asymmetric allylations of benzaldehyde with
allylsilane 2a–2c in the presence of 1a or 1b were investigated to study the influence
of the various allylsilane reagents (Table 1). The reactions were conducted using a stoi-
chiometric amount of the Lewis base in dichloromethane at ꢀ78ꢁC for 3 days. After
workup, the corresponding homoallylic alcohol was obtained only in the case of entry
2. The product was purified by flash column chromatography (n-hexane=dichloro-
methane 2=1), and the Lewis base was recovered nearly quantitatively by changing
the eluent to CH3COOEt on the same column. The enantiomeric ratios were
determined by chiral high-performance liquid chromatographic (HPLC) analysis.
Table 1. Asymmetric allylation of benzaldehyde with allylsilanes 2a–2c in the presence of Lewis basesa
Entry
Lewis base
Allylsilane
Er (R=S)b
Yield (%)c
1
2
3
4
1a
1b
1b
1b
2a
2a
2b
2c
—
36:64
—
0
63
0
—
0
aReaction performed with 0.5 mmol of Lewis base, 0.5 mmol of benzaldehyde, and 1.5 mmol of allylsi-
lane in dichloromethane (2 mL) at ꢀ78 ꢁC for 3 days.
bDetermined by Daicel Chiralcel OD (n-hexane=i-PrOH ¼ 19=1).
cIsolated yields after column chromatography.

ASYMMETRIC ALLYLATION OF BENZALDEHYDE
3629
Scheme 2. Preparation of Lewis bases 1c–1i.
To improve the enantioselectivities, we next prepared various Lewis bases 1c–1i
having substituents on the nitrogen atoms (Scheme 2). Bisformylation of (R,R)-1,2-
cyclohexanediamine with acetic formic anhydride followed by reduction with lithium
aluminum hydride gave (R,R)-N,N0-dimethyl-1,2-diaminocyclohexane by a method
similar to that in Ref. 7e. Again, bisformylation of the resulting diamine with acetic
formic anhydride afforded the Lewis base 1c in 46% overall yield. The coupling reac-
tion of 1,2-cyclohexanediamine with bromobenzene followed by bisformylation pro-
vided the corresponding Lewis base 1d. Lewis bases 1e–1i were obtained in 25–87%
overall yields by formation of imines, reduction with NaBH4,[7c] and bisformylation
as in the method of 1c and 1d.
Allylations with 1c–1i were conducted using a method similar to that used in
Table 1 except for the amount of Lewis bases (Table 2). Interestingly, the major
enantiomer in all cases was R, which was opposite that of entry 2 in Table 1. The
reason for this is not clear; however, the chirality on the nitrogen atoms by chirality
transfer[15] in the transition state would be different from the case in Table 1. From
optimization of the reaction conditions, it was found that 5 equiv. of Lewis base to
aldehyde was necessary for greater yields of the product (entries 2 and 4–9 in
Table 2). Although allylation with Lewis base 1c having methyl groups on the

3630
K. ISHIMARU ET AL.
Table 2. Asymmetric allylation of benzaldehyde with allyltrichlorosilane in the presence of Lewis basea
Entry
Lewis base (equiv. to aldehyde)
Er (R=S)b
Yield (%)c
1
2
3
4
5
6
7
8
9
1c (1)
1c (5)
1d (1)
1d (5)
1e (5)
1f (5)
1g (5)
1h (5)
1i (5)
58:42
58:42
79:21
79:21
60:40
67:33
70:30
44:56
83:17
14
75
19
80
91
81
71
88
90
aReaction performed with Lewis base (0.5 mmol or 2.5 mmol), 0.5 mmol of benzaldehyde, and 1.5 mmol
of allyltrichlorosilane in dichloromethane (2 mL) at ꢀ78 ꢁC for 3 days.
bDetermined by Daicel Chiralcel OD (n-hexane=i-PrOH ¼ 19=1).
cIsolated yields after column chromatography (n-hexane=dichloromethane ¼ 2=1).
nitrogen atoms gave a 58:42 (R=S) ratio of the product, the use of 1d having benzyl
substituents afforded a greater enantiomeric ratio (R=S 79:21, 80% yield in entry 4).
The best result was obtained with Lewis base 1i (R=S ¼ 83:17, 90% yield in entry 9).
Allylations with Lewis bases having bulky substituents on the benzyl groups did not
give good results (entries 7 and 8). We also explored the influence of various addi-
tives such as molecular sieves, Na2SO4, hexamethyl phosphoramide (HMPA), or dii-
sopropylethylamine; however, the enantiomeric ratios were nearly the same, and the
yields were poor, showing these additives did not accelerate the reaction. We also
conducted the reaction of m-tolualdehyde in the presence of Lewis base 1i, and high
enantiomeric ratio was obtained (R=S ¼ 92:8,[15] 100% isolated yield). The reaction
of o-tolualdehyde using 1i gave a 57:43 (R=S) ratio of the product in quantitative
yield. Absolute configuration of the major enantiomer was assigned by comparing
the retention time as in Ref. 5a.
In conclusion, we have first prepared the novel chiral C2-symmetric bisforma-
mides and explored their use in the allylation of benzaldehydes with allyltrichlorosi-
lane. Further studies to investigate the reaction mechanism and applications are now
in progress.
EXPERIMENTAL
All reactions were performed under an argon atmosphere in dried flasks, and
the components were added by means of syringes. All solvents were dried by stan-
1
dard methods. H NMR spectra were recorded at 300 MHz (JEOL JNM-AL300
BK1) in CDCl3. Compound 1a and (1R,2R)-N,N0-dimethyl-1,2-cyclohexanediamine
were prepared according to the method in Ref. 7e (supporting information), and the
spectral data were identical with those in Refs. 7e and 7c, respectively.

ASYMMETRIC ALLYLATION OF BENZALDEHYDE
3631
Typical Experimental Procedure for Reaction of Benzaldehyde with
Allyltrichlorosilane in the Presence of Lewis Base 1
Benzaldehyde (0.051 mL, 0.5 mmol) at room temperature was added to a stir-
red solution of Lewis base 1 (2.5 mmol) in dry dichloromethane (2 mL). The solution
was cooled to ꢀ78 ꢁC, and then allylsilane (1.5 mmol) was slowly added. The reac-
tion mixture was stirred atꢀ78 ꢁC for 3 days and quenched with 2 mL of aqueous
saturated NaHCO3. The mixture was extracted with dichloromethane (10 mL ꢂ 3),
and the combined organic layers were dried over Na2SO4. The precipitates were
filtered off, and the solvent was evaporated to give the crude product. The
crude product was purified by flash column chromatography on SiO2(n-hexane=
dichloromethane ¼ 2=1), and isolated yields were measured. The spectral data of
the homoallylic alcohol was consistent with the data in Ref. 5a (supporting infor-
mation). The enantiomeric ratio was determined by a chiral column (Daicel Chiralcel
OD, n-hexane=i-PrOH 19=1).
Data
Compound 1b. 1H NMR (300 MHz, CDCl3): d 1.31–1.50 (m, 4H), 1.65–1.92
(m, 2H), 2.04–2.08 (m, 2H), 3.75–3.88 (m, 2H), 5.95–6.20 (m, 2H), 8.15 (brs, 2H).
HRMS-FAB(Mþ): Obsd. m=z 170.1063. Calcd. for C8H14N2O2: 170.1055.
Compound 1c. 1H NMR (300 MHz, CDCl3): d 1.20–1.50 (m, 2H), 1.51–2.06
(m, 6H), 2.81 (s, 3H), 2.85 (s, 3H), 4.40–4.52 (m, 2H), 7.93–8.17 (m, 2H).
HRMS-FAB(Mþ): Obsd. m=z 198.1375. Calcd. for C10H18O2N2: 198.1368.
(1R,2R)-N,N’-Diphenyl-1,2-cyclohexanediamine. 1H NMR (300 MHz,
CDCl3): d 1.10–1.25 (m, 2H), 1.35–1.50 (m, 2H), 1.73–1.79 (m, 2H), 2.33–2.37 (m,
2H), 3.12–3.25 (m, 2H), 3.75–3.88 (m, 2H), 6.61–6.75 (m, 5H), 7.14–7.28 (m, 5H).
HRMS-FAB(Mþ): Obsd. m=z 266.1771. Calcd. for C18H22N2: 266.1783.
Compound 1d. 1H NMR (300 MHz, CDCl3): d 1.20–1.45 (m, 4H), 1.50–1.65
(m, 2H), 1.91–2.08 (m, 2H), 4.52–4.75 (m, 2H), 7.21–7.44 (m, 10H), 8.21 (s, 2H)
(8.42, s, rotamer). HRMS-FAB(Mþ): Obsd. m=z 322.1680. Calcd. for
C20H22O2N2: 322.1681.
(1R,2R)-N,N’-Dibenzyl-1,2-cyclohexanediamine. 1H NMR (300 MHz,
CDCl3): d 1.10–1.25 (m, 4H), 1.73–1.79 (m, 2H), 2.13–2.25 (m, 2H), 2.33–2.40 (m,
2H), 2.50–2.85 (brm, 2H), 3.67 (d, 2H, J ¼ 9.7 Hz), 3.97 (d, 2H, J ¼ 9.7 Hz),
7.28–7.32 (m, 10H). HRMS-FAB(Mþ): Obsd. m=z 294.2082. Calcd. for C20H26N2:
294.2096.
Compound 1e. 1H NMR (300 MHz, CDCl3): d 1.06–1.35 (m, 4H), 1.45–1.79
(m, 6H), 4.18–4.26 (m, 2H), 4.28–4.40 (m, 2H), 7.17–7.35 (m, 10H), 8.16–8.31 (m,
2H). HRMS-FAB(Mþ): Obsd. m=z 350.2001. Calcd. for C22H26O2N2: 350.1994.
(1R,2R)-N,N’-Bis(3,3-dimethylbutyl)-1,2-cyclohexanediamine. 1H NMR
(300 MHz, CDCl3): d 0.93 (s, 18H), 1.21–1.34 (m, 2H), 1.42–1.60 (m, 6H), 1.76–1.91
(m, 2H), 2.22–2.31 (m, 2H), 2.55–2.80 (m, 4H), 2.93–3.06 (m, 2H), 3.70–4.05 (brs,
2H). HRMS-FAB(Mþ): Obsd. m=z 282.3029. Calcd. for C18H38N2: 282.3035.

3632
K. ISHIMARU ET AL.
Compound 1f. 1H NMR (300 MHz, CDCl3): d 0.94 (s, 18H), 1.15–1.50 (m,
6H), 1.62–2.08 (m, 8H), 2.80–3.24 (m, 2H), 3.26–3.52 (m, 2H), 7.99–8.07 (m, 2H).
HRMS-FAB(Mþ): Obsd. m=z 338.2929. Calcd. for C20H38O2N2: 338.2933.
(1R,2R)-N,N’-Bis[(4-t-butylphenyl)methyl]-1,2-cyclohexanediamine.
1H NMR (300 MHz, CDCl3): d 1.31 (s, 18H), 1.25–1.35 (m, 4H), 1.73–1.82 (m, 2H),
2.13–2.27 (m, 2H), 2.45–2.55 (m, 2H), 3.68 (d, 2H, J ¼ 13.0 Hz), 3.96 (d, 2H,
J ¼ 13.0 Hz), 7.23 (d, 4H, J ¼ 8.1 Hz), 7.36 (d, 4H, J ¼ 8.1 Hz). HRMS-FAB(Mþ):
Obsd. m=z 406.3355. Calcd. for C28H42N2: 406.3348.
Compound 1g. 1H NMR (300 MHz, CDCl3): d 1.28 (s, 18H), 1.15–1.32 (m,
4H), 1.51–1.92 (m, 6H), 4.35–4.42 (m, 2H), 4.60–4.66 (m, 2H), 7.09–7.36 (m, 8H),
8.15–8.26 (m, 2H). HRMS-FAB(Mþ): Obsd. m=z 462.3252. Calcd. for
C30H42O2N2: 462.3246.
(1R,2R)-N,N’-Bis[(3,5-di-t-butylphenyl)methyl]-1,2-cyclohexanediamine.
1H NMR (300 MHz, CDCl3): d 1.26 (s, 36H), 1.22–1.32 (m, 2H), 1.47–1.58 (m, 2H),
1.82–1.85 (m, 2H), 2.25–2.29 (m, 2H), 2.65–2.68 (m, 2H), 3.80 (d, 2H, J ¼ 12.8 Hz),
4.10 (d, 2H, J ¼ 12.8 Hz), 7.11–7.35 (m, 6H). HRMS-FAB(Mþ): Obsd. m=z
518.4611. Calcd. for C36H58N2: 518.4600.
Compound 1h. 1H NMR (300 MHz, CDCl3): d 1.24 (s, 18H), 1.32 (s, 18H),
1.48–1.80 (m, 10H), 3.72–3.75 (m, 2H), 4.41–4.46 (m, 2H), 6.92–7.42 (m, 6H),
8.25–8.30 (m, 2H). HRMS-FAB(Mþ): Obsd. m=z 574.4493. Calcd. for
C38H58O2N2: 574.4498.
(1R,2R)-N,N’-Bis[(2-methylphenyl)methyl]-1,2-cyclohexanediamine.
1H NMR (300 MHz, CDCl3): d 1.12–1.35 (m, 4H), 1.73–1.85 (m, 2H), 2.30 (s, 6H),
2.29–2.42 (m, 4H), 2.80 (brs, 2H), 3.65 (d, 2H, J ¼ 13.1 Hz), 3.93 (d, 2H, J ¼ 13.1 Hz),
7.14–7.26 (m, 8H). HRMS-FAB(Mþ): Obsd. m=z 322.2417. Calcd. for C22H30N2:
322.2409.
Compound 1i. 1H NMR (300 MHz, CDCl3): d 1.18–1.38 (m, 6H), 1.26 (s,
6H), 1.50–1.75 (m, 4H), 4.40–4.47 (m, 2H), 4.63–4.75 (m, 2H), 6.85–7.40 (m, 8H),
8.20–8.32 (m, 2H). HRMS-FAB(Mþ): Obsd. m=z 378.2300. Calcd. for
C24H30O2N2: 378.2307.
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