Mild and efficient allylation of aldehydes by using copper fluorapatite as catalyst

Article abstract of DOI:10.1002/adsc.200800159

A facile synthesis of homoallylic alcohols is achieved by the allylation of aldehydes with allylicmetal reagents or allyl halides using copper fluorapatite (CuFAP) as catalyst under mild reaction conditions. A variety of aldehydes were converted to the co

Full text of DOI:10.1002/adsc.200800159

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DOI: 10.1002/adsc.200800159
Mild and Efficient Allylation of Aldehydes by using Copper
Fluorapatite as Catalyst
M. Lakshmi Kantam,a,* G. T. Venkanna,a K. B. Shiva Kumar,a
V. Balasubrahmanyam,a G. Venkateswarlu,a and B. Sreedhara
a
Inorganic and Physical Chemistry Division, Indian Institute of Chemical Technology, Hyderabad – 500 007, India
Fax : (+91)-40-2716-0921; e-mail: mlakshmi@iict.res.in
Received: March 16, 2008; Revised: May 28, 2008; Published online: June 20, 2008
Abstract: A facile synthesis of homoallylic alcohols
is achieved by the allylation of aldehydes with allyl-
icmetal reagents or allyl halides using copper fluor-
lation in heterogenous media involving SnO and cata-
lyticCu O.[19] However, in the above methods the use
2
of an organic co-solvent such as THF was necessary.
Guo et al. reported the SnCl2-mediated carbonyl ally-
lation in aqueous media using various Lewis acid ad-
ditives.[20]
The development of more improved synthetic
methods for the preparation of homoallylicalochols
remains an active research area.
ACHTREUNGapatite (CuFAP) as catalyst under mild reaction
conditions. A variety of aldehydes were converted
to the corresponding homoallylic alchohols, demon-
strating the versatility of the reaction.
Keywords: aldehydes; allylation; copper fluorapa-
tite; homoallylicalcohols
Apatites are basicmetal phosphates for which the
chemical formula is
M10ACHTREGNU(PO4)6(X)2 [M=divalent
metal, X=monovalent anion] and various kinds of
cations and anions can be readily introduced into
their frameworks due to their large ion exchange abil-
ity and such exchanged apatites are already in use in
Allylation of aldehydes by various allylicmetals is an
important synthetictransformation
[1]
[21,22]
as the resultant several organictransformations.
Very recently, we
homoallylicalochols are versatile synthons in the
reported the preparation of recyclable, heterogeneous,
preparation of materials, natural products, bioactive Cu-exchanged fluorapatite and copper exchanged tert-
compounds and many complex molecules.[2] The gen- butoxyapatite catalysts, for the N-arylation of imida-
eral practice for the preparation of homoallylic alco- zoles and other heterocycles with iodo-, bromo-,
hols involves nucleophilic addition of an allylic metal chloro- and fluoroarenes (EW) with good to excellent
reagent to carbonyl compounds. Previously, numerous yields.[23a,b] We also reported the PdFAP catalyst
reports on such transformations carried out using var- (fluorACHTREaUNG patite-supported palladium catalyst) for Suzuki
ious Lewis acids, Brønsted acids,[3] metal salts,[4] b-cy- and Heck coupling reactions.[23c]
clodextrin,[5] organometallicreagents in organic
We herein report a convenient method involving
[6]
media, aqueous media, ionicliquids
and PEG[7] the use of the CuFAP catalyst for the allylation of al-
have been published. The Barbier reaction[8] is an al- dehydes with allyltributylstannane or allytrimethylsi-
ternative method for the synthesis of homoallylical-
lane (Scheme 1) and Barbier-type allylation of car-
cohols, this is the reaction of a carbonyl compound bonyl compounds with allyl halides for the synthesis
with an organichalide in the presence of magnesium
metal. Aluminum,[9] magnesium,[10] manganese,[11]
of homoallylic alcohols (Scheme 2).
In an effort to evolve a better catalytic system, vari-
indium,[12] antimony,[13] bismuth,[14] lead,[15] gallium,[16] ous reaction parameters were screened in the allyla-
zinc,[17] and tin[18] mediated Barbier reactions in aque- tion reaction between benzaldehyde and allyltributyl-
ous medium are well known in the literature. Al- stannane and it was found that CuFAP catalyst in
though good yields can often be obtained in these re-
actions, the use of zero-valent metals causes metal
oxide or hydroxide precipitation on the surface of the
metal in some cases which leads to termination or in-
creased duration of ther reaction. Furthermore, some
zero-valent metals are too reactive and significant by-
products like pinacol can be produced in the reaction.
Roy et al. reported the first example of carbonyl ally- and allytrimethylsilane catalyzed by CuFAP.
Scheme 1. Allylation of aldehydes with allyltributylstannane
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In order to understand the scope and limitations of
the CuFAP-catalyzed allylation reaction, various
structurally divergent aldehydes possessing a wide
range of functional groups were reacted with allyltri-
butylstannane and allytrimethylsilane to give the cor-
responding homoallylicalochols and the results are
summarized in Table 1.
Scheme 2. Barbier-type allylation of aldehydes catalyzed by
CuFAP.
As per expectation, aldehydes with an electron-do-
DMSO at 608C afforded good yields of the desired nating group gave lower yields of the desired product
product. Allyltrimethysilane also reacted equally well whereas the presence of electron-withdrawing groups
with benzaldehyde under similar conditions with good produced better yields (Table 1, entries 1–8).
yields of corresponding homoallylic alcohols. The con-
Heteroaromatic aldehydes such as 4-pyridinecar-
trolled reaction conducted under identical conditions boxaldehyde, 2-pyridine-carboxaldehyde and 2-fural-
devoid of CuFAP did not give any product despite dehyde (Table 1, entries 9–12), gave good yields of
prolonged reaction times. CuFAP was recovered the corresponding homoallylic products with shorter
quantitatively by simple centrifugation and reused for reaction times. Highly conjugated aromatics like cin-
four cycles with consistent activity (Table 1, entry 1), namaldehyde and aliphatic aldehydes such as cyclo-
moreover, the absence of copper in the filtrate was hexanecarboxaldehyde and propionaldehyde afforded
demonstrated by AAS which confirms no leaching of moderate yields of the corresponding homoallylic al-
copper during the reaction and provides evidence for cohols after long reaction durations (Table 1, en-
heterogeneity throughout the reaction.
tries 13 and 14).
Impressed by the results on the allylation reaction
with allyltributylstannane and allytrimethylsilane, we
further extended the scope of our catalytic system for
the Barbier-type allylation of carbonyl compounds
with allyl halides mediated by SnCl2 in aqueous
media.
Table 1. Allylation of carbonyl compounds with allyltributyl-
stannane and allytrimethylsilane catalyzed by CuFAP.[a]
In an effort to develop a better catalytic system,
various catalysts were screened in the allylation reac-
tion between 4-chlorobenzaldehyde and allyl bromide
in the presence of SnCl2 in water and the results are
summarized in Table 2. CuFAP, afforded very good
yields whereas CuHAP (copper hydroxyapatite) and
homogeneous CuACHTRE(UNG OAc)2 provided moderate yields.
Other supported copper catalysts such as Cu/NaY,
Cu/SiO2, Cu/Al2O3, and Cu/TiO2 were also screened
and the results are summarized in Table 2. The order
of efficiency is CuFAP>Cu/NaY>CuHAP>Cu/
TiO2 >CuACHTREU(GN OAc)2 >Cu/Al2O3 >Cu/SiO2. There is no
reaction in the control experiment conducted in the
absence of catalyst under identical conditions. CuFAP
was recovered quantitatively by simple filtration and
reused with consistent activity (Table 2, entry 2).
We chose a variety of structurally divergent alde-
hydes possessing a wide range of functional groups
for our study to understand the scope and the gener-
ality of the CuFAP-catalyzed allylation of aldehydes
and the results are summarized in Table 3. Among
the various aldehydes tested, heteroaromaticalde-
hydes such as 4-pyridinecarboxaldehyde, 2-pyridine-
carboxaldehyde
and
3-pyridinecarboxaldehyde
(Table 3, entries 12–14) gave very good yields of the
coupling product with shorter duration of reaction.
Allylation was slow with 2-naphthaldehyde when
compared with the other aromatic aldehydes (Table 3,
entry 11). Electron-donating groups on the aromatic
[a]
Reaction conditions: aldehyde (1 mmol), allylicmetal re-
agent (1.2 mmol), CuFAP (0.1 g), DMSO (3 mL), 608C.
Isolated yields
Yield after fourth cycle.
[b]
[c]
[d]
Reaction conditions: aldehyde (10 mmol), allylicmetal
reagent (12 mmol), CuFAP (1 g), DMSO (30 mL), 608C. ring gave lower yields of desired product compared
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Mild and Efficient Allylation of Aldehydes by using Copper Fluorapatite
COMMUNICATIONS
Table 2. Allylation of 4-chlorobenzaldehyde with allyl bro-
Table 3. Allylation of aldehydes catalyzed by CuFAP.[a]
mide using different catalysts.[a]
[a]
Reaction conditions: 4-chlorobenzaldehyde (1 mmol),
allyl bromide (1.2 mmol), copper (0.073 mmol), water
(1 mL), reaction time (1.5 h), room temperature.
Isolated yields.
Yield after third cycle.
10 mol% catalyst.
[b]
[c]
[d]
with electron-withdrawing groups which produced
better yields with shorter reaction time (Table 3, en-
tries 1–7, 10 and 19). Nitrobenzaldehyde gave the de-
sired product in excellent yields without reduction of
nitro group (Table 3, entry 3). Aliphaticaldehydes
such as propionaldehyde, heptaldehyde and cyclohex-
anecarboxaldehyde gave satisfactory yields with
longer reaction times (Table 3, entries 20–22). Never-
theless, the CuFAP-catalyzed allylation does not work
efficiently for ketones. Among the various allyl hal-
ides used, allyl bromide proved to be a good allylating
agent in the above reaction (Table 3, entry 1).
[a]
Reaction conditions: aldehyde (1 mmol), allyl halide
(1.2 mmol), catalyst (0.1 g), water (1 mL), room tempera-
ture.
Isolated yield with allyl bromide as allylating agent.
Isolated yield with allyl chloride as allylating agent.
[b]
[c]
[d]
Isolated yield with allyl iodide as allylating agent.
Isolated yields.
[e]
In order to study the effect of the CuFAP catalyst
on the regio- and diasteroselectivities of the allylation
reaction, we have carried out a reaction between cin-
namyl bromide and benzaldehyde in the presence of
SnCl2/CuFAP under similar reaction conditions. It is hydes with allyltributylstannane and allytrimethylsi-
well known in the literature that allylation reactions lane, we further tried to extend the scope of the ally-
involving cinnamyl halides can provide both a- and g- lation to 2,3-O-isopropylidene-1-O-methyl-R-d-xylo-
adducts. The g-adduct can be either the anti- or syn- pentodialdo-1,4-furanose (Scheme 4). We obtained
product (Scheme 3). The reaction with CuFAP cata- good yields of the corresponding homoallylic alcohol
lyst gave an 80% yield in which the g-adduct is ob- with a diastereomericratio 1.8:1 (diastereomericratio
tained as the favorable isomer (98% determined by of the product was calculated by proton NMR). Stud-
1
300 MHz H NMR) with good diasteroselectivity to ies on the allylations of various sugar aldehydes using
the anti-product (85% determined by 300 MHz CuFAP catalyst are under progress.
1H NMR).
In conclusion, we have developed a simple and effi-
Encouraged by the results of the allylation of aro- cient method for the preparation of homoallylic alco-
matic, aliphatic, conjugated and heteroaromatic alde- hols from aldehydes and allyltributylstannane or ally-
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Scheme 3. Barbier-type allylation of benzaldehyde with cinnamyl bromide catalyzed by CuFAP.
copper contents in the fresh and the used catalyst (CuFAP)
were analyzed by AAS and the leaching of copper is about
1.2% after the Barbier-type allylation reaction.
Typical Procedure for Allylation of Benzaldehyde
with Allyltributylstannane
CuFAP (100 mg) was added to a mixture of benzaldehyde
(1 mmol) and allyltributylstannane (1.2 mmol) in DMSO
(3 mL). The mixture was stirred for an appropriate time at
room temperature. After completion of the reaction, as indi-
cated by TLC, the reaction mixture was quenched with
aqueous sodium hydrogen carbonate and extracted with
ethyl acetate (3”10 mL). The combined organic extract was
dried over anhydrous sodium sulfate and concentrated
under reduced pressure to give the crude product. The
crude product was purified by column chromatography on
silica gel (hexane/ethyl acetate, 90/10) to afford pure 1-
Scheme 4. Allylation of mannose aldehyde (2,3-O-isopropy-
lidene-1-O-methyl-R-d-xylo-pentodialdo-1,4-furanose) with
allyltributylstannane catalyzed by CuFAP.
trimethylsilane using the CuFAP catalyst. Various
structurally divergent aldehydes were reacted with al-
lyltributylstannane and allytrimethylsilane to yield the
corresponding homoallylic alcohols with moderate to
excellent yields (80–97%). The Barbier-type allylation
of carbonyl compounds with allyl halides was also car-
ried out with this catalyst. This catalyst offers several
advantages including mild reaction conditions, shorter
reaction times, good yields of the products with low
catalytic loading. We believe that this methodology
will find widespread use in organicsynthesis for the
preparation of homoallylicalcohols.
1
(phenyl)-3-buten-1-ol. H NMR (300 MHz, CDCl3): d=2.32
(br, s 1H), 2.44 (t, J=6.7 Hz, 2H), 4.62 (t, J=6.7 Hz, 1H),
5.04–5.14 (m, 2H), 5.65–5.82 (m, 1H), 7.18–7.32 (m, 5H).
Typical Procedure for CuFAP/SnCl2-Mediated
Carbonyl Allylation
CuFAP (100 mg) was added to a mixture of 4-chlorobenzal-
dehyde (1 mmol), allyl bromide (1.2 mmol) and tin chloride
(1.2 mmol) in water (1.5 mL). The mixture was stirred for
1 h at room temperature. After completion of the reaction,
as indicated by TLC, the product was extracted with ethyl
acetate (3”10 mL). The combined extract was concentrated
under vacuum and the resulting product was purified by
column chromatography on silica gel with ethyl acetate and
n-hexane as eluent to afford pure 1-(4-chlorophenyl)-3-
buten-1-ol. 1H NMR (300 MHz, CDCl3): d=1.90–2.32 (br,
1H), 2.45(dd, J=5.63, 6.64 Hz, 2H), 4.68(t, J=7.29 Hz, 1H),
5.15 (t, J=11.7 Hz, 2H), 5.66–5.83 (m, 1H), 7.21–7.32 (m,
4H). The products were characterized by comparison of
their NMR and mass spectra with those of authentic sam-
ples.[25–27]
Experimental Section
Typical Procedure for Preparation of Copper
Fluorapatite
Calcium fluorapatite [Ca10CAHTRE(UNG PO4)6(F)2] was synthesized ac-
cording to the literature procedure.[24] CaFAP (1 g) was
stirred with aqueous copper acetate (400 mg, 2 mmol in
25 mL water) at 808C for a period of 10 h. The slurry ob-
tained was filtered, washed with deionized water, and dried
overnight at 1108C, yielding copper-exchanged fluorapatite
as a blue powder. Copper-exchanged fluorapatite (CuFAP)
was characterized by XPS, AAS and IR. XPS analysis of the
CuFAP catalyst indicated the same binding energy values
for Ca, P and O as in CaFAP. A narrow scan of Cu 2p3/2 for
CuFAP showed the binding energy peak at 934.9 eV [the
binding energy of Cu in Cu(II) is around 935 eV],[19] which
indicates copper in the +2 oxidation state in CuFAP. The
Acknowledgements
G.T.Vthanks CSIR India for an SRF fellowship.
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ꢀ 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Adv. Synth. Catal. 2008, 350, 1497 – 1502