Rhodium-catalyzed rearrangement of aryl bis(alkynyl) carbinols to 3-alkynyl-1-indanones

Article abstract of DOI:10.1002/anie.200704818

(Chemical Equation Presented) Ten little indanones: The title reaction (see scheme; Si = trialkylsilyl) is proposed to go through a pathway involving a β-carbon elimination/carborhodation sequence. Ready access to the carbinol substrates from an aromatic ester and a terminal alkyne makes the present catalysis reaction an efficient way of preparing 3-alkynyl-1-indanones.

Full text of DOI:10.1002/anie.200704818

Angewandte
Chemie
DOI: 10.1002/anie.200704818
Carborhodation
Rhodium-Catalyzed Rearrangement of Aryl Bis(alkynyl) Carbinols to
3-Alkynyl-1-indanones**
Ryo Shintani,* Keishi Takatsu, Taisuke Katoh, Takahiro Nishimura, and Tamio Hayashi*
A transition-metal-catalyzed isomerization or rearrangement
can provide an efficient way to convert readily accessible
organic compounds into those with more structural complex-
ity under mild conditions.[1] For example, rhodium-catalyzed
isomerization of secondary propargyl alcohols to the corre-
sponding a,b-unsaturated ketones was described,[2] and a
reaction pathway involving b-hydrogen elimination of an
alkoxorhodium species with subsequent hydrorhodation of an
Table 1: Rhodium-catalyzed rearrangement of 1 to indanones 2.
alkyne was proposed (Scheme 1a).[2b] This reaction sequence
Entry Substrate
Ligand Product Yield [%][a]
1
1a (R=H, Si=SiMe2(tBu))
1a
1a
1a
1a
1a
1b (R=H, Si=SiEt3)
1c (R=H, Si=Si(nPr)3)
1d (R=2-Me, Si=SiMe2(tBu))
1e (R=4-Me, Si=SiMe2(tBu))
1 f (R=4-OMe, Si=SiMe2(tBu)) binap 2 f
1g (R=4-F, Si=SiMe2(tBu))
1h (R=4-Cl, Si=SiMe2(tBu))
none
PPh3
dppb
dppp
binap 2a
binap 2a
binap 2b
binap 2c
binap 2d
binap 2e
2a
2a
2a
2a
(5)
(19)
(9)
(45)
73
79
63
66
85
71
87
85
84
2[b]
3
Scheme 1. a) Proposed reaction pathway for the rhodium-catalyzed
isomerization of secondary propargyl alcohols; b) possible reaction
pathway for the potential rhodium-catalyzed rearrangement of tertiary
propargyl alcohols.
4
5
6[c]
7
8
9
10
11
12
13
was applied to the synthesis of 1-indanones by employing a-
aryl propargyl alcohols.[3] In contrast, an analogous process
with tertiary propargyl alcohols involving b-carbon elimina-
tion[4] and successive carborhodation has yet to be reported
(Scheme 1b).[5] Within this context we describe the develop-
ment of a rhodium-catalyzed rearrangement of readily
available aryl bis(alkynyl) carbinols to 3-alkynyl-1-indanones
under mild conditions.
binap 2g
binap 2h
[a] Yield of isolated product. Numbers in parentheses were determined
by using 1H NMR spectroscopy with an internal standard (MeNO2).
[b] 16 mol% of ligand wasused. [c] The reaction wasconducted on a
5.0 mmol scale.
Initially, we prepared phenyl bis((tert-butyldimethylsil-
yl)ethynyl) carbinol (1a) as a model substrate [Eq. (1)] and
treated it with [{Rh(OH)(cod)}2] (8 mol% Rh) at 508C
(Table 1, entry 1). Under these conditions indanone 2a was
obtained in only 5% yield. The use of PPh3 as a ligand gave a
somewhat better yield (19%) of 2a (Table 1, entry 2), and use
of dppb as the ligand resulted in a low yield of 9% (Table 1,
entry 3). In both cases the major component after the reaction
was unreacted 1a. In contrast, the yield of 2a was improved
by using other bisphosphine ligands such as dppp and binap,
giving a 45% yield (Table 1, entry 4) and a 73% yield
(Table 1, entry 5), respectively. The present reaction of 1a can
be easily scaled up to 5 mmol, and leads to 79% yield of 2a
(Table 1, entry 6). Under the reaction conditions using binap
as the ligand, substrates derived from triethylsilyl- and tri-n-
propylsilylacetylenes (1b and 1c) also underwent the rear-
rangement to give indanones 2b and 2c, respectively (63–
66% yield; Table 1, entries 7 and 8). In addition, various
substituents on the aromatic ring of the substrate were
tolerated, giving the corresponding indanones in high yield
(71–87% yield; Table 1, entries 9–13).[6]
[*] Dr. R. Shintani, K. Takatsu, T. Katoh, Dr. T. Nishimura,
Prof. Dr. T. Hayashi
Department of Chemistry
Graduate School of Science
Kyoto University
Sakyo, Kyoto 606-8502 (Japan)
Fax: (+81)75-753-3988
E-mail: shintani@kuchem.kyoto-u.ac.jp
thayashi@kuchem.kyoto-u.ac.jp
[**] Support provided in part by a Grant-in-Aid for Scientific Research,
the Ministry of Education, Culture, Sports, Science, and Technology
(Japan) (21 COE on Kyoto University Alliance for Chemistry).
A proposed catalytic cycle of this process is illustrated in
Scheme 2. Alkoxorhodium species A, which is initially
Supporting information for thisarticle isavailable on the WWW
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Scheme 3. Proposed reaction pathway for the formation of 3a.
significant advantage for the efficient synthesis of 3-alkynyl-1-
indanones.
The same mode of rearrangement is also observed with
substrate 1i which has 1-cyclohexenyl group at the bis(pro-
pargylic) position, giving cyclopentenone derivative 2i in
66% yield [Eq. (3)]. This outcome represents a rare example
Scheme 2. Proposed catalytic cycle of the rhodium-catalyzed rearrange-
ment of 1 to 2. [Rh]=Rh(binap), Si=Si(alkyl)3.
generated from the hydroxorhodium catalyst and substrate
1a, undergoes b-alkynyl elimination to give intermediate B.[7]
Alkynylrhodation of B to the conjugated alkyne generates
alkenylrhodium species C with subsequent 1,4-rhodium
migration to form arylrhodium intermediate D.[3,8] This
intermediate undergoes intramolecular 1,4-addition (arylrho-
dation) to give oxa-p-allylrhodium E with subsequent proto-
nolysis by alcohol 1 to produce indanone 2 and regenerate
alkoxorhodium A.
It is worth comparing the present rearrangement with an
intermolecular reaction between an aryl alkynyl ketone and a
terminal alkyne,[9] which in principle can also provide the
same 3-alkynyl-1-indanone as the product.[8d,e] In reality,
however, a reaction of 3-(tert-butyldimethylsilyl)-1-phenyl-2-
propyn-1-one with (tert-butyldimethylsilyl)acetylene in the
presence of a Rh/binap catalyst gave almost no indanone 2a
and the major products were uncyclized conjugated ynenone
3a (52% yield) and alkyne dimer 4 (26% yield) [Eq. (2)].[10]
that involves 1,4-rhodium migration from an alkenyl carbon
atom to another alkenyl carbon atom.
In summary, we have developed a rhodium-catalyzed
rearrangement of aryl bis(alkynyl) carbinols to 3-alkynyl-1-
indanones through a pathway involving a b-carbon elimina-
tion/carborhodation sequence under mild conditions. Con-
sidering the ease of the synthesis of carbinol substrates from
an aromatic ester and a terminal alkyne in a single step, the
present catalysis provides an efficient way of preparing 3-
alkynyl-1-indanones.
Experimental Section
General procedure for Table 1: A solution of [{Rh(OH)(cod)}2]
(3.6 mg, 16 mmol Rh) and ligand (18 mmol) in 1,4-dioxane (3.0 mL)
was stirred for 20 min at room temperature. Compound 1 (0.20 mmol)
was added with additional 1,4-dioxane (2.0 mL) and the mixture was
stirred for 48 h at 508C. The reaction was quenched with water and
extracted with Et2O. The organic layer was dried over MgSO4,
filtered, and concentrated under vacuum. The residue was purified by
silica gel preparative TLC with EtOAc/hexanes to afford product 2.
The use of deuterated (tert-butyldimethylsilyl)acetylene in
this reaction revealed that the deuterium was mostly incor-
porated at the alkenyl carbon atom adjacent to the carbonyl
group of product 3a. This result indicates that the ligand
exchange between alkenylrhodium intermediate C and a
terminal alkyne occurs faster than the 1,4-rhodium migration
from C to D, suppressing the subsequent formation of
indanone 2a (Scheme 3, see also Scheme 2). Because a free
terminal alkyne does not exist in the rearrangement of aryl
bis(alkynyl) carbinols, our newly developed catalysis has a
Received: October 17, 2007
Published online: January 10, 2008
Keywords: b-carbon elimination · indanones· rearrangement ·
.
rhodium
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[6] a) To date we have not been successful in employing carbon-
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hexyne-derived carbinol gives indanone in 15% yield with
significant decomposition of the substrate; b) The use of
enantiopure (S)-binap as a ligand gives the product with
moderate enantioselectivity (e.g., 34% ee for indanone 2 f).
[7] a) A. Funayama, T. Satoh, M. Miura, J. Am. Chem. Soc. 2005,
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