Chromium(ii)-mediated reactions of iodonium tetrafluoroborates with aldehydes: Umpolung of reactivity of diaryl-, alkenyl(aryl)-, and alkynyl(aryl)iodonium tetrafluoroborates

Article abstract of DOI:10.1021/jo990809y

The method described herein allows us, for the first time, to perform umpolung of reactivity of diaryl-, alkenyl(aryl)-, and alkynyl(aryl)iodonium tetrafluoroborates. The method involves generation of organochromium(III) species via reaction of iodonium salts with anhydrous chromium dichloride, followed by their nucleophilic addition to aldehydes to yield alcohols. In contrast to the reaction of aryl and alkenyl halides with chromium dichloride, these iodonium salts are so active that organochromium(III) could be generated without using a nickel catalyst. Substituent effects of unsymmetrically substituted diaryliodonium salts on the product profiles are in good agreement with the reported mode of decomposition of the intermediate unsymmetrical diaryliodanyl radicals. Alkenyl(mesityl)iodonium tetrafluoroborates undergo exclusive alkenylation of aldehydes with no signs of the formation of an arylation product.

Full text of DOI:10.1021/jo990809y

6804
J . Org. Chem. 1999, 64, 6804-6814
Ch r om iu m (II)-Med ia ted Rea ction s of Iod on iu m Tetr a flu or obor a tes
w ith Ald eh yd es: Um p olu n g of Rea ctivity of Dia r yl-, Alk en yl(a r yl)-,
a n d Alk yn yl(a r yl)iod on iu m Tetr a flu or obor a tes
Da-Wei Chen and Masahito Ochiai*
Faculty of Pharmaceutical Sciences, University of Tokushima, 1-78 Shomachi,
Tokushima 770-8505, J apan
Received May 17, 1999
The method described herein allows us, for the first time, to perform umpolung of reactivity of
diaryl-, alkenyl(aryl)-, and alkynyl(aryl)iodonium tetrafluoroborates. The method involves generation
of organochromium(III) species via reaction of iodonium salts with anhydrous chromium dichloride,
followed by their nucleophilic addition to aldehydes to yield alcohols. In contrast to the reaction of
aryl and alkenyl halides with chromium dichloride, these iodonium salts are so active that
organochromium(III) could be generated without using a nickel catalyst. Substituent effects of
unsymmetrically substituted diaryliodonium salts on the product profiles are in good agreement
with the reported mode of decomposition of the intermediate unsymmetrical diaryliodanyl radicals.
Alkenyl(mesityl)iodonium tetrafluoroborates undergo exclusive alkenylation of aldehydes with no
signs of the formation of an arylation product.
In tr od u ction
as carbonyl compounds. An efficient method for this
purpose remains to be established.
Iodonium salts such as diaryl-, alkenyl(aryl)-, and
alkynyl(aryl)iodonium salts are known to be versatile
agents in organic synthesis.1 Because of their highly
electron-deficient nature and the excellent nucleofugality
of the phenyliodonio group, which shows a leaving group
ability about 106 times greater than triflate,2 these
iodonium salts serve as the highly activated species of
halides in nucleophilic substitution reactions. For in-
stance, diaryliodonium salts transfer the aryl group to a
variety of organic substrates including carbon, nitrogen,
phosphorus, and group 16 element-centered nucleophiles
under mild conditions.1 Alkenyl(aryl)iodonium salts also
undergo nucleophilic vinylic substitutions with a number
of nucleophiles such as organocuprates, sulfinates, thi-
olates, nitrites, halides, cyanides, azides, phosphines, and
enolates.3 Similarly, reaction of alkynyl(aryl)iodonium
salts with nucleophiles affords substituted alkynes.
Although a stepwise pathway including Michael addition
followed by carbene rearrangement has been established,
the alkynyliodonium salts formally act as alkynyl cation
synthons in these reactions.1 No strategy is available,
however, for using these iodonium salts as an anion-
equivalent species that can react with electrophiles such
Chromium-mediated coupling of organic halides with
aldehydes, reported by Nozaki, Hiyama, and co-workers
in 1977, is a useful method for carbon-carbon bond
formation because of its excellent chemoselectivity for
aldehydes as well as its compatibility with other func-
tional groups, e.g., esters, amides, nitriles, ketones,
alcohols, and various alcohol protecting groups.4 The
reaction involves intermediacy of organochromium(III)
species, which act as carbanion equivalents.5 Takai and
Kishi independently demonstrated that the reaction of
aryl and alkenyl halides (I and Br) with CrCl2 requires
a catalytic amount of nickel salts for efficient generation
of the nucleophilic organochromium(III) intermediates.6
This reaction is believed to proceed via oxidative addition
(3) (a) Ochiai, M.; Sumi, K.; Takaoka, Y.; Kunishima, M.; Nagao,
Y.; Shiro, M.; Fujita, E. Tetrahedron 1988, 44, 4095. (b) Ochiai, M.;
Oshima, K.; Masaki, Y. J . Am. Chem. Soc. 1991, 113, 7059. (c) Ochiai,
M.; Oshima, K.; Masaki, Y. Tetrahedron Lett. 1991, 32, 7711. (d) Ochiai,
M.; Oshima, K.; Masaki, Y.; Kunishima, M.; Tani, S. Tetrahedron Lett.
1993, 34, 4829. (e) Ochiai, M.; Oshima, K.; Masaki, Y. Chem. Lett. 1994,
871. (f) Zefirov, N. S.; Kozmin, A. S.; Kasumov, T.; Potekhin, K. A.;
Sorokin, V. D.; Brel, V. K.; Abramkin, E. V.; Struchkov, Y. T.;
Zhdankin, V. V.; Stang, P. J . J . Org. Chem. 1992, 57, 2433. (g) Ochiai,
M.; Shu, T.; Nagaoka, T.; Kitagawa, Y. J . Org. Chem. 1997, 62, 2130.
(h) Okuyama, T.; Takino, T.; Sato, K.; Ochiai, M. J . Am. Chem. Soc.
1998, 120, 2275.
* To whom correspondence should be addressed. Tel: 88-633-7281.
Fax: 88-633-9504. E-mail: mochiai@ph2.tokushima-u.ac.jp.
(1) For reviews, see: (a) Koser, G. F. The Chemistry of Functional
Groups, Supplement D; Wiley: New York, 1983; Chapter 25. (b) Ochiai,
M.; Nagao, Y. J . Synth. Org. Chem., J pn. 1986, 44, 660. (c) Ochiai, M.
Rev. Heteroatom Chem. 1989, 2, 92. (d) Moriarty, R. M.; Vaid, R. K.
Synthesis 1990, 431. (e) Moriarty, R. M.; Vaid, R. K.; Koser, G. F.
Synlett. 1990, 365. (f) Varvoglis, A. The Chemistry of Polycoordinated
Iodine; VHC Publishers: New York, 1992. (g) Kita, Y.; Tohma, H.;
Yakura, T. Trends Org. Chem. 1992, 3, 113. (h) Stang, P. J . Angew.
Chem., Int. Ed. Engl. 1992, 31, 274. (i) Koser, G. F. The Chemistry of
Functional Groups, Supplement D2; Wiley: New York, 1995; Chapter
21. (j) Kitamura, T. J . Synth. Org. Chem., J pn. 1995, 53, 893. (k) Stang,
P. J .; Zhdankin, V. V. Chem. Rev. 1996, 96, 1123. (l) Ochiai, M.
Chemistry of Hypervalent Compounds; Akiba, K., Eds.: Wiley-VCH:
New York, 1999; Chapter 12.
(4) (a) Okude, Y.; Hirano, S.; Hiyama, T.; Nozaki, H. J . Am. Chem.
Soc. 1977, 99, 3179. (b) Hiyama, T.; Okude, Y.; Kimura, K.; Nozaki,
H. Bull. Chem. Soc. J pn. 1982, 55, 561. (c) For catalytic version of the
chromium-mediated coupling of organic halides with aldehydes, see:
Furstner, A.; Shi, N. J . Am. Chem. Soc. 1996, 118, 2533. Furstner, A.;
Shi, N. J . Am. Chem. Soc. 1996, 118, 12349. Grigg, R.; Putnikovic, B.;
Urch, C. J . Tetrahedron Lett. 1997, 38, 6307.
(5) For reviews, see: (a) Hiyama, T. J . Synth. Org. Chem., J pn. 1981,
39, 81. (b) Takai, K.; Utimoto, K. J . Synth. Org. Chem., J pn. 1988, 46,
66. (c) Saccomano, N. A. In Comprehensive Organic Synthesis; Trost,
B. M., Fleming, I., Eds.; Pergamon: Oxford, 1991; Vol. 1, pp 173-
209. (d) Cintas, P. Synthesis 1992, 248.
(6) (a) Takai, K.; Kimura, K.; Kuroda, T.; Hiyama, T.; Nozaki, H.
Tetrahedron Lett. 1983, 24, 5281. (b) Takai, K.; Tagashira, M.; Kuroda,
T.; Oshima, K.; Utimoto, K.; Nozaki, H. J . Am. Chem. Soc. 1986, 108,
6048. (c) J in, H.; Uenishi, J .; Christ, W. J .; Kishi, Y. J . Am. Chem.
Soc. 1986, 108, 5644. (d) Stamos, D. P.; Sheng, C.; Chen, S. S.; Kishi,
Y. Tetrahedron Lett. 1997, 38, 6355.
(2) Okuyama, T.; Takino, T.; Sueda, T.; Ochiai, M. J . Am. Chem.
Soc. 1995, 117, 3360.
10.1021/jo990809y CCC: $18.00 © 1999 American Chemical Society
Published on Web 08/11/1999

Chromium(II)-Mediated Reactions of IodoniumTetrafluoroborates
J . Org. Chem., Vol. 64, No. 18, 1999 6805
Ta ble 1. Ch r om iu m -Med ia ted Ar yla tion of Ald eh yd es 2 w ith Dia r yliod on iu m Sa lts 1a
iodonium salt
Ar
aldehyde
R
product (102 mol)b
b
b
CrCl2
NiCl2
conditions
T/°C, time/h
entry
1
molb
2
(mol)
(mol)
3c
ArId
ArHd
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
1a
1a
1a
1a
1a
1a
1a
1a
1a
1a
1a
1a
1a
1a
1a
1a
1a
1a
1b
1c
Ph
0.5
0.5
0.5
1
2
1
1.5
2
2
1
1
1
1
1.5
1
1
1.5
2
1.5
1
2a
2a
2a
2a
2a
2a
2a
2a
2a
2b
2c
2d
2e
2f
2g
2h
2i
2j
2a
2a
Ph
4
4
4
4
4
4
6
8
8
4
4
4
4
6
4
4
6
4
6
4
0.02
0.02e
0.02f
0
25, 5
25, 24
25, 5
25, 5
25, 5
25, 5
25, 5
0, 5
0, 24
25, 5
25, 5
25, 5
25, 5
25, 5
25, 5
25, 5
25, 5
25, 5
25, 5
25, 5
3a (57)
3a (59)
3a (48)
3a (69)
3a (72)
3a (87)
3a (92)
3a (62)
3a (86)
3b (82)
3c (78)
3d (72)
3e (79)
3f (82)
3g (74)
3h (0)g
3i (71)
3j (56)
3b (79)
3c (72)
2
24
5
33
17
39
34
140
44
153
40
44
42
34
-
84
168
35
24
200
200
49
66
-
0
0.02
0.03
0.04
0.04
0.02
0.02
0.02
0.02
0.03
0.02
0.02
0.03
0
p-ClC6H4
p-MeC6H4
p-MeOC6H4
o-MeC6H4
n-C10H21
Me2CH
t-Bu
E-MeCHdCH
E-PhCHdCH
-
-
64
-
30
-
47
-
-
-
-
-
p-ClC6H4
p-MeC6H4
0.03
0.02
36
73
-
41
a
b
Reactions were carried out using 0.3 mmol of an aldehyde in DMF under Ar. Molar ratios per mol of an aldehyde. c Isolated yields.
GC yields. -: not determined. e Reactions were carried out in DMSO under Ar. f Reactions were carried out in the presence of excess
amounts of 1,1-diphenylethylene. Benzhydrol (3a ) (10%) and benzophenone (8%) were obtained.
d
g
Sch em e 1
yield, in addition to benzene (33%). When DMSO was
used as a solvent, a similar yield (59%) of 3a was obtained
along with the formation of iodobenzene (24%) and
benzene (17%).
Significantly, in marked contrast to the reaction of aryl
halides with CrCl2, we found that the iodonium salt 1a
is so active that phenylchromium(III) could be generated
from 1a without using a nickel catalyst.10 Thus, reaction
of 1a (1 equiv) with benzaldehyde (2a ) using CrCl2 (4
equiv) at room temperature afforded benzhydrol (3a ) in
69% yield (Table 1, entry 4). One of the byproducts of
this reaction was found to be a large amount (84%) of
iodobenzene that is incapable of generating phenylchro-
mium(III) without a Ni catalyst under these conditions.6
Use of a catalytic amount of NiCl2 as an additive made
it possible to use both of the phenyl moieties in 1a , which
resulted in a much improved yield of 3a (87%) and a
decreased amount (35%) of iodobenzene (Table 1, entry
6). At 0 °C, however, the nickel catalyst no longer
effectively activates iodobenzene (Table 1, entries 8 and
9). Use of 1a (1.5 equiv)/ CrCl2 (6 equiv)/NiCl2 (0.03 equiv)
at room temperature afforded a 92% yield of 3a , but with
formation of a large amount of benzene. The original
reactions between aryl halides and aldehydes require 2
molar equiv of the halides for an efficient coupling;6
therefore, this result probably indicates a competing side
reaction, i.e., reductive dehalogenation of aryl halides
leading to arenes.
of a halide to Ni(0) generated by reduction of Ni(II) with
2 molar equiv of CrCl2, followed by transmetalation
reaction with Cr(III), yielding organochromium(III)
(Scheme 1).
We report herein, for the first time, chromium(II)-
mediated reactivity umpolung of aryl-, alkenyl-, and
alkynyliodonium tetrafluoroborates, which involves in-
termediacy of organochromium(III) followed by nucleo-
philic addition to aldehydes to yield alcohols.7 Because
of its moderate reducing power as a single-electron-
transfer agent,8 commercially available anhydrous CrCl2
was used for reduction of these iodonium salts.9
Resu lts a n d Discu ssion
Rea ction of Dia r yliod on iu m Sa lts: Ch r om iu m -
Med ia ted Ar yla tion of Ald eh yd es. The results of
reactions of diaryliodonium tetrafluoroborates 1 with
CrCl2 in the presence of an aldehyde are summarized in
Table 1. Our initial results (Table 1, entry 1) indicated
that generation of the phenylchromium(III) species could
be achieved by using diphenyliodonium tetrafluoroborate
(1a ) under conventional conditions, i.e., CrCl2 and a
catalytic amount of NiCl2 in DMF at room temperature
for 5 h; thus, in the presence of benzaldehyde (2a ),
reaction of the iodonium salt 1a (0.5 equiv) afforded
benzhydrol (3a ) as a product of an addition reaction of
the resulting phenylchromium(III) intermediate in 57%
In general, the reaction was carried out by adding a
solution of an aldehyde 2 and diphenyliodonium salt 1a
in DMF to a solution of CrCl2 doped with NiCl2 in DMF
at room temperature under argon. As shown in Table 1,
the phenylchromium(III) generated from 1a readily
undergoes additions to aromatic aldehydes 2b-e with
electron-withdrawing and -donating substituents as well
as aliphatic aldehydes 2f,g to give the alcohols 3 in good
yields. With R,â-unsaturated aldehydes, selective 1,2-
(7) A part of this work has been reported in a preliminary form:
Chen, D.-W.; Takai, K.; Ochiai, M. Tetrahedron Lett. 1997, 38, 8211.
(8) Hanson, J . R. Synthesis 1974, 1.
(9) Reduction of diphenyliodonium chloride with CrCl2 in water has
been reported to give benzene. See: Beringer, F. M.; Bodlaender, P.
J . Org. Chem. 1969, 34, 1981.
(10) It has been documented that, in some cases, commercially
available CrCl2 contains nickel salts as an impurity.6b,c The chromium
reagent used in our studies was purchased from Kishida Chemical Co.
and was not efficient in converting iodobenzene to phenylchro-
mium(III).

6806 J . Org. Chem., Vol. 64, No. 18, 1999
Ta ble 2. P r od u ct Distr ibu tion in Ar yla tion of 2a w ith Un sym m etr ica l Dia r yliod on iu m Sa lts 4a
product (yield/%), ratio
Chen and Ochiai
entry
4
3a b
3b
ratioc
PhHd
ArHd
ratioe
ArId
PhId
ratiof
1
2
3
4
5
4a
3a (60)
3a (46)
3a (56)
3a (42)
3a (26)
3d (20)
3d (15)
3k (0)
3c (24)
3b (31)
75:25
75:25
100:0
64:36
46:54
PhH (4)
PhH (5)
PhH (15)
PhH (3)
PhH (17)
PhOMe (6)
PhOMe (3)
1,3,5-Me3C6H3 (7)
PhMe (15)
71:29
74:26
92:8
54:46
45:55
p-MeOC6H4I (69)
p-MeOC6H4I (74)
2,4,6-Me3C6H2I (81)
p-MeC6H4I (58)
p-ClC6H4I (26)
PhI (16)
PhI (15)
PhI (19)
PhI (23)
PhI (44)
81:19
83:17
81:19
72:28
37:63
4a g
4b
4c
4d
PhCl (21)
a
b
d
Reaction conditions: 2a /4 (1 molar equiv)/CrCl2(4 molar equiv)/DMF/25 °C/5 h/Ar. Isolated yields. c Ratios of 3a :3b-d ,k ,l. GC
yields. e Ratios of (3a + PhH):(3b-d ,k ,l + ArH). f Ratios of ArI:PhI. Reactions were carried out at 0 °C for 24 h.
g
Sch em e 2
Sch em e 4
Sch em e 3
No reaction of phenylchromium(III) with 3-pentanone
and N-(benzenesulfonyl)benzaldimine was observed un-
der our conditions. The reaction with hexanoyl chloride
afforded the desired 1-phenylhexan-1-one (23%) accom-
panied by the formation of benzhydrol (3a ) (8%), ben-
zophenone (4%), and N,N-dimethylhexanamide (9%).
To investigate the electronic and steric effects of
substituents on the aromatic rings of diaryliodonium
salts and to gain some insight into the mechanism of this
reaction (see below), we analyzed in detail (see Table 2)
product compositions for the chromium-mediated cou-
pling of unsymmetrically substituted aryl(phenyl)iodo-
nium salts 4 with benzaldehyde (2a ) in the absence of
Ni catalyst (Scheme 4).
Reaction of p-methoxyphenyl(phenyl)iodonium salt 4a
gave rise to the phenylation product 3a as a major
product (60%) and the substituted benzhydrol 3d as a
minor product (20%), accompanied by the formation of
dehalogenated arenes (PhH, 4%; PhOMe 6%) and iodo-
arenes (p-MeOC6H4I, 69%; PhI, 16%) (Table 2, entry 1).
Use of p-methylphenyliodonium salt 4c gave similar
results, but with reduced selectivity. Interestingly, mesi-
tyl(phenyl)iodonium salt 4b gave benzhydrol (3a ) selec-
tively with no sign of the formation of substituted 3k (Ar
) 2,4,6-Me3C6H2). We have no evidence for the formation
of mesitylchromium(III) in this reaction, but, even if it
is formed,15 severe steric congestion derived from the
vicinal methyl groups of mesitylchromium(III) would
probably inhibit the addition reaction to benzaldehyde
(2a ).16 Thus, the electron-donating methoxy or methyl
group afforded a larger amount of benzhydrol (3a ) than
substituted benzhydrols. On the other hand, introduction
of an electron-withdrawing p-chloro group reversed the
major reaction course, with the substituted 3b predomi-
nating. These substituent effects on the product profiles
are in good agreement with the reported mode of decom-
position of unsymmetrical diaryliodanyl radicals (see
below).17
addition to the carbonyl groups was observed; for ex-
ample, (E)-crotonaldehyde (2i) afforded the benzyl alcohol
3i selectively in 71% yield (Table 1, entry 17). Cinnam-
aldehyde (2j), however, gave poor results (less than 10%
yield of 3j) under our standard conditions, probably
because of its high propensity to undergo reductive
coupling with CrCl2 in DMF yielding glycols.11 This
problem was overcome by adding 2j into the reaction
system containing pregenerated phenylchromium(III) in
the absence of an excess Cr(II), and an acceptable yield
of 3j was achieved via the exclusive 1,2-addition (Table
1, entry 18). Substituted phenylchromium species with
p-chloro and p-methyl groups could also be generated
from diaryliodonium salts 1b,c and reacted with 2a
affording addition products in good yields (Table 1,
entries 19 and 20).
The sterically demanding compounds, pivalaldehyde
(2h ), did not react with phenylchromium(III) under our
conditions. In this reaction, small amounts of benzhydrol
(3a ) (10%) and benzophenone (8%) were isolated. These
products were proved to be derived from the reaction of
phenylchromium(III) with DMF, because the reaction
shown in Scheme 3 resulted in formation of the same
product mixture in comparable yields in the absence of
an aldehyde. DMF has been shown to be a solvent of
choice in chromium-mediated coupling of alkenyl and aryl
halides with aldehydes because of the high solubility of
CrCl2.6 These results might suggest, however, that DMF
itself can act as an electrophile toward phenylchro-
mium(III).12 In fact, it has been shown that DMF is a
good ligand to octahedral chromium(III),14 which, by
activating DMF, would facilitate its reaction with phen-
ylchromium(III).
(11) This reductive coupling of cinnamaldehyde (2j) by the reaction
with CrCl2 in DMF is fast (within 5 min at 25 °C) and gives a
stereoisomeric mixture of pinacol-type dimers via the ketyl radical
anion in good yields. For pinacol coupling of aldehydes with Cr(II),
see: (a) Ho, T.-L. Synthesis 1979, 1. (b) Conant, J . B.; Cutter, H. B. J .
Am. Chem. Soc. 1926, 48, 1016. (c) Davis, D. D.; Bigelow, W. B. J .
Am. Chem. Soc. 1970, 92, 5127.
Rea ction of Alk en yl(a r yl)iod on iu m Sa lts: Ch r o-
m iu m -Med ia ted Alk en yla tion of Ald eh yd es. Alkenyl-
(12) In this reaction, benzaldehyde (2a ) is probably produced in situ
by nucleophilic attack of phenylchromium intermediate to DMF
followed by extrusion of dimethylamine. Reaction of phenylchro-
mium(III) with benzaldehyde (2a ) gives chromium alkoxide of benz-
hydrol (3a ). â-Hydrogen abstraction from this chromium alkoxide
intermediate will produce benzophenone, as was reported by Yama-
moto.13
(14) (a) Daly, J . J .; Sneeden, R. P. A.; Zeiss, H. H. J . Am. Soc. Chem.
1966, 88, 4287. (b) Hiyama, T.; Kimaru, K.; Nozaki, H. Tetrahedron
Lett. 1981, 22, 1037.
(15) The observed formation both of mesitylene and iodobenzene in
this reaction suggests the intervention of mesitylchromium(III).
(16) Lack of formation of the substituted benzhydrol 3k may reflect
the lifetime of the transient mesitylchromium(III). See: Hodgson, D.
M.; Wells, C. Tetrahedron Lett. 1994, 35, 1601.
(13) Ito, T.; Ono, T.; Maruyama, K.; Yamamoto, A. Bull. Chem. Soc.
J pn. 1982, 55, 2212.

Chromium(II)-Mediated Reactions of IodoniumTetrafluoroborates
J . Org. Chem., Vol. 64, No. 18, 1999 6807
Sch em e 5
iodonium salts 5 are summarized in Table 4. The cyclo-
hexenylchromium(III) generated from 5a c readily un-
dergoes addition to aromatic aldehydes 2a -c as well as
aliphatic aldehydes 2g,i,k , yielding the allyl alcohols 6
in good yields (Table 4, entries 1-6). (E)-Crotonaldehyde
(2i) underwent selective 1,2-addition to the carbonyl
group and, after quenching of the reaction mixture with
an aqueous NaHCO3 solution, afforded the allyl alcohol
6l selectively in 67% yield (Table 4, entry 5). When the
reaction mixture was quenched with water, formation of
a considerable amount of the conjugated dienyl alcohol
8 (16%) was observed in addition to the allyl alcohol 6l
(55%). The alcohol 8 would be a thermodynamic product,
formed by acid-catalyzed rearrangement of the allyl
alcohol 6l during workup using water (Scheme 6). It has
been shown that an aqueous solution of CrCl3 is moder-
ately acidic.18 (E)-Styryl(mesityl)iodonium tetrafluoro-
borate (5h c) gave the alkenylation product 3j in low yield
(15%) and (E)-â-chlorostyrene as a major product (49%).
Rea ction of Alk yn yl(a r yl)iod on iu m Sa lts: Ch r o-
m iu m -Mediated Alkyn ylation of Aldeh ydes. 1-Alkyn-
yl iodides are reduced with CrCl2 in DMF to give
alkynylchromium(III), which adds to aldehydes to yield
propargyl alcohols.19 The results of alkynylation of benz-
aldehyde (2a ) with 1-decynyl(phenyl)iodonium tetrafluo-
roborate (9) are summarized in Table 5. Reaction of an
equivalent amount of the alkynyliodonium salt 9 with
2a in the presence of CrCl2 and NiCl2 in DMF at 25 °C
afforded the alkynylation product, propargyl alcohol 10,
in 29% yield along with the formation of a small amount
of alkynyl ketone 11 (5%) (Scheme 7; Table 5, entry 1).13
Use of 2 equiv of 9 increased the yield of 10 (59-63%,
Table 5, entries 2 and 3). Interestingly, this alkynylation
of 2a appears to be highly selective in the sense that we
did not observe phenylation of 2a to yield 3. This
observation is in a good agreement with formation of a
large amount of iodobenzene.
DMSO as a solvent gave comparable results; however,
other solvents such as THF, PhH, CH2Cl2, and MeOH
afforded no evidence of alkynylation (Table 5, entries
5-8). MeOH resulted in exclusive reduction, affording
1-decyne (12) in 85% yield.20 When the reaction was
carried out in CH2Cl2, extensive halogen exchange was
observed: that is, 1-chlorodecyne (13) was obtained
selectively in 80% yield along with iodobenzene (83%).
PhH as a solvent gave similar results. Such halogen
exchanges have been observed in the reaction of primary
alkyl iodides with CrCl2 in DMF that results in the
formation of alkyl chlorides.21b,22
(aryl)iodonium salts 5 were also reduced at room tem-
perature with CrCl2 in DMF without using NiCl2.
Alkenylation yielding allyl alcohols 6 and arylation
yielding benzhydrols 3 compete each other in the reaction
with benzaldehyde (2a ) (Scheme 5); thus, treatment of
an equivalent amount of 4-tert-butylcyclohexenyl(phenyl)-
iodonium tetrafluoroborate (5a a ; Ar ) Ph) with 2a in the
presence of CrCl2 afforded a mixture of the alkenylation
product, allyl alcohol 6a , and the arylation product,
benzhydrol (3a ), in a ratio of 45:55 in good yield (Table
3, entry 1). Iodobenzene and cyclohexenyl iodide 7a were
also obtained in a comparable ratio. Introduction of a
p-methoxy substituent into the phenyl group of 5a a
increased the selectivity for alkenylation of 2a , and the
allyl alcohol 6a was obtained as a major product in 48%
yield, with a 75:25 ratio of alkenylation to arylation. Use
of 4-tert-butylcyclohexenyl(mesityl)iodonium tetrafluo-
roborate (5a c; Ar ) 2,4,6-Me3C6H2) gave the alkenylation
product 6a selectively with no sign of the formation of
the arylation product 3k (Table 3, entry 3). These results
are in good agreement with the substituent effects shown
in Table 2.
Compared to the results obtained with cyclohexenyl-
iodonium salts 5a , those obtained in the reaction of
cyclopentenyliodonium tetrafluoroborates 5ba and 5bc
with benzaldehyde (2a ) were poor, probably due to the
difference in stability between cyclohexenyl and cyclo-
pentenyl radicals. Acyclic alkenyliodonium salt does not
seem to be a suitable substrate for this chromium-
mediated coupling with 2a . (E)-1-Decenyl(phenyl)iodo-
nium salt 5ca afforded a mixture of the allyl alcohol 6c
and benzhydrol (3a ) with a 24:76 ratio in 34% yield
(Table 3, entry 7). Furthermore, no alkenylation products
were obtained in the reaction of (Z)-2-halo-1-decenyl-
(phenyl)iodonium salts 5ea and 5fa , and the reactions
afforded a large amount of 1-decyne in 31-69% yield
through syn â-elimination.
The results of chromium-mediated alkenylations of
various aldehydes 2 using 2 equiv of alkenyl(mesityl)-
Rea ction Mech a n ism . A. Dia r yliod on iu m Sa lt. As
illustrated in Scheme 8, the reaction mechanism for the
(18) Yamada, Y. Haiikagoubutu no Kagaku; Kagakudojin: Tokyo,
1980.
(19) Takai, K.; Kuroda, T.; Nakatsukasa, S.; Oshima, K.; Nozaki,
H. Tetrahedron Lett. 1985, 26, 5585.
(20) Reaction of phenylchromium(III) with methanol proceeds at
room temperature and gives benzene. See ref 13.
(21) (a) Crandall, J . K.; Michaely, W. J . J . Org. Chem. 1984, 49,
4244. (b) Takai, K.; Nitta, K.; Fujimura, O.; Utimoto, K. J . Org. Chem.
1989, 54, 4732.
(22) Takai, K.; Matsukawa, N.; Takahashi, A.; Fujii, T. Angew.
Chem., Int. Ed. Engl. 1998, 37, 152.
(17) Generation of diaryliodanyl radicals has been well documented.
(a) In nucleophilic substitutions: Tanner, D. D.; Reed, D. W.; Setiloane,
B. P. J . Am. Chem. Soc. 1982, 104, 3917. Singh, P. R.; Khanna, R. K.
Tetrahedron Lett. 1982, 23, 5355. Beringer, F. M.; Falk, R. A. J . Chem.
Soc. 1964, 4442. (b) Under photochemical conditions: Crivello, J . V.
Adv. Polym. Sci. 1984, 62, 1. Crivello, J . V. Annu. Rev. Mater. Sci.
1983, 13, 173. Kampmeier, J . A.; Nalli, T. W. J . Org. Chem. 1994, 59,
1381. Kampmeier, J . A.; Nalli, T. W. J . Org. Chem. 1993, 58, 943. (c)
In electrochemical reductions: Mubarak, M. S.; Peters, D. G. J . Org.
Chem. 1985, 50, 673.

6808 J . Org. Chem., Vol. 64, No. 18, 1999
Chen and Ochiai
Ta ble 3. Ch r om iu m -Med ia ted Cou p lin g of Ben za ld eh yd e 2a w ith Alk en yl(a r yl)Iod on iu m Sa lts 5a
iodonium salt
product (yield/%), ratio
ratioc ArId
entry
5
Ar
6b
3b
7d
ratioe
1
2
3
4
5
6
7
8
9
5a a
5a b
5a c
Ph
6a (35)
6a (48)
6a (62)
6b (0)
3a (43)
3d (16)
3k (0)
3a (49)
3k (0)
3a (26)
3k (0)
3k (0)
45:55
75:25
100:0
0:100
100:0
24:76
100:0
100:0
0:100
0:100
100:0
PhI (39)
7a (61)b
7a (23)b
7a (11)b
7b (13)
7b (22)
7c (63)b
7c (36)b
7d (34)
7e (15)
7f (13)
39:61
72:28
87:13
19:81
61:39
22:78
64:36
66:34
85:15
85:15
91:9
p-MeOC6H4
2,4,6-Me3C6H2
Ph
2,4,6-Me3C6H2
Ph
2,4,6-Me3C6H2
2,4,6-Me3C6H2
Ph
Ph
Ph
p-MeOC6H4I (58)b
2,4,6-Me3C6H2I(72)b
PhI(3)
5ba
5bcf
5ca f
5ccf
5d cf
5ea f
5fa f
5ga f
6b (8)
2,4,6-Me3C6H2I (35)
PhI (18)
6cg (8)
6cg (23)
6d (12)
6eg (0)
6fg (0)
2,4,6-Me3C6H2I (64)b
2,4,6-Me3C6H2I (66)
PhI (84)
3a (9)
3a (6)
3a (trace)
10
11
PhI (76)
PhI (74)
6gg (12)
7g (0)
a
b
d
Reaction conditions: 2a /5 (1 molar equiv)/CrCl2(4 molar equiv)/DMF/25 °C/5 h/Ar. Isolated yields. c Ratios of 6:3. GC or 1H NMR
yields. e Ratios of ArI:7. f 2 equiv of CrCl2 was used. Formation of 1-decyne (12) was observed: entry 6, 5%; entry 7, 7%; entry 9, 31%;
g
entry 10, 69%; entry 11, 22%.
Ta ble 4. Ch r om iu m -Med ia ted Alk en yla tion of Ald eh yd es
2 w ith Alk en yl(m esityl)iod on iu m Sa lts 5a
the decomposition of the divalent radicals 15 favors
cleavage of the Ar-I bond if the aryl groups have
electron-withdrawing substituents but cleavage of the
Ph-I bond if the aryl groups have electron-donating
substituents (Scheme 9).17 The relative ratios of rate
constants k2/k1 were calculated from the relative yields
of iodoarenes shown in Table 2 and compared with the
reported values (Table 6). The relative rates of aryl
radical departure k2/k1 obtained for the chromium-
mediated reaction of phenyl(tolyl)- 4c and anisyl(phenyl)-
iodonium salts 4a are in good agreement with the
reported values of decomposition of unsymmetrical di-
aryliodanyl radicals 15 generated by single-electron
transfer from sodium phenoxide or di-tert-butyl nitrox-
ide.17a The selectivity observed may be attributable to the
differences in bond dissociation energies of aryl carbon-
iodine bonds.24 These results would suggest the involve-
ment of the [9-I-2] iodanyl radical 15 in this chromium-
mediated coupling.
entry
5
2 (R)
2a (Ph)
6
yieldb/%
1
2
3
4
5
6
7
8
9
5a c
5a c
5a c
5a c
5a c
5a c
5bc
5cc
5d c
5h c
6a
6i
6j
6k
6l
6m
6b
6c
6d
3j
81
77
72
70
67
72
21
40
27
15e
2b (p-ClC6H4)
2c (p-MeC6H4)
2g (Me2CH)
2i (E-MeCHdCH)c
2k (n-C9H19
2a (Ph)
2a (Ph)
)
2a (Ph)
10
2a (Ph)d
a
Reaction conditions: 2/5 (2 molar equiv)/CrCl2(4 molar equiv)/
DMF/25 °C/5 h/Ar. Isolated yields. c The reaction mixture was
quenched with an aqueous NaHCO3 solution. Reaction condi-
b
d
tions: 2a /5h c (1 molar equiv)/CrCl2(2 molar equiv)/DMF/25 °C/5
h/Ar. e (E)-â-Chlorostyrene was obtained in 49% yield.
Sch em e 6
A Hammett plot of log(k2/k1) vs σ is linear with F )
2.04 and correlation coefficient ) 0.99. In the unimolecu-
lar decomposition of the [9-I-2] intermediate 15 to yield
aryl radicals, involvement of a polar transition state 16
has been proposed (Scheme 10).17a,25 This partial charge
separation predicts a decomposition pathway favoring
cleavage of the Ar-I bond when the aryl groups have
electron-withdrawing substituents, which is in a good
agreement both with the observed departure aptitudes
k2/k1 of the chromium-mediated reaction of 4 and with
the positive F value of the Hammett plots.
Both the formyl and methyl groups of DMF act as a
good hydrogen atom donor toward carbon- and oxygen-
centered radicals (Ph•, HO•, and t-BuO•).26 Formation of
a considerable amount of the reduced arenes as byprod-
ucts (Table 1) might partly involve the intervention of
aryl radicals, which will abstract hydrogen from the
solvent DMF; when Cr-mediated coupling of 1a with 2a
was performed in DMF-d7, GC-MS analysis showed a
20% deuterium incorporation in the byproduct benzene.
This hydrogen abstraction from DMF by aryl radicals
would compete with the reduction by Cr(II) that yields
the arylchromium(III).
Cr-mediated coupling of diaryliodonium salts 1 with
aldehyde 2 might be assumed to involve reduction of the
hypervalent iodine generating the [9-I-2]23 iodanyl radical
14 via a single-electron transfer from Cr(II).17 Unimo-
lecular decomposition of the iodanyl radical 14 will
produce both aryl radical and aryl iodide. Further reduc-
tion of the aryl radical with Cr(II) generates arylchro-
mium(III), which reacts with aldehydes 2 yielding the
alcohol 3. The arylchromium(III) is also produced from
the aryl iodide, when Ni catalyst is present;6 in fact,
formation of a large amount of iodobenzene was observed
in the reaction of diphenyliodonium salt 1a with benzal-
dehyde (2a ) without using a nickel catalyst, whereas a
reduced amount of iodobenzene along with an increased
yield of 3a was produced in the presence of Ni(II)
(compare entries 4 and 6 in Table 1).
Several experimental observations are in line with this
proposed mechanism. It has been well established that
unsymmetrically substituted [9-I-2] aryl(phenyl)iodanyl
radicals 15 would decompose by two paths, one leading
to phenyl radical and iodoarene and the other to aryl
radical and iodobenzene. It has also been established that
(24) The bond dissociation energies of aryl carbon-iodine bond in
homolysis follow the order: PhI < p-MeC6H4I < p-MeOC6H4I.17a,25
(25) (a) Danen, W. C.; Saunders: D. G. J . Am. Chem. Soc. 1969,
91, 5924. (b) Davis, W. H.; Gleaton, J . H.; Pryor, W. A. J . Org. Chem.
1977, 42, 7.
(23) For nomenclature, see: Perkins, C. W.; Martin, J . C.; Arduengo,
A. J .; Lau, W.; Alegria, A.; Kochi, J . K. J . Am. Chem. Soc. 1980, 102,
7753.
(26) (a) Gardini, G. P.; Minisci, F.; Palla, G.; Arnone, A.; Galli, R.
Tetrahedron Lett. 1971, 59. (b) Doyle, M. P.; Dellaria, J . F.; Siegfried,
B.; Bishop, S. W. J . Org. Chem. 1977, 42, 3494.

Chromium(II)-Mediated Reactions of IodoniumTetrafluoroborates
Ta ble 5. Ch r om iu m -Med ia ted Alk yn yla tion of Ald eh yd e 2a w ith Alk yn yliod on iu m Sa lt 9a
product (102 mol)b
J . Org. Chem., Vol. 64, No. 18, 1999 6809
b
b
entry
9b (mol)
CrCl2 (mol)
NiCl2 (mol)
solvent
conditions time/h
10c
11c
12d
13d
PhId
1
2
3
4
5
6
7
8
1
2
2
1
1
1
1
1
2
4
4
2
2
2
2
2
0.01
0
DMF
DMF
DMF
DMSO
THF
PhH
CH2Cl2
MeOH
5
5
5
5
5
30
30
30
29
63
59
17
0
0
0
0
5
6
4
0
0
0
0
0
29
31
80
42
32
8
12
0
0
100
184
186
89
75
80
0.02
0.01
0.01
0.01
0.01
0.01
3
12
50
80
02
3
85
83
86
a
b
Reactions were carried out using 0.3 mmol of benzaldehyde (2a ) in DMF at 25 °C under Ar. Molar ratios per mol of 2a . c Isolated
d
yields. GC yields.
Sch em e 7
Sch em e 10
Sch em e 11
Sch em e 8
Sch em e 9
Ta ble 6. Rela tive Ra tios of Ra te Con sta n ts k2/k1 for
Decom p osition of 15
reagent
conditions
p-MeO
p-Me
p-Cl
Cr(II)a
DMF/25 °C
H2O/60 °C
hν/H2O/60 °C
hν/acetone/25 °C
0.24
0.093
0.10
0.61
0.39
0.30
0.34
0.85
2.42
c
PhONab
t-Bu2NO•b
Ph3Pd
-
-
and the cyclized reduced product, 3-methyl-2,3-dihy-
drobenzofuran (19) (9%).21 Increased amounts (24%) of
19 were obtained when the reaction was carried out in
DMF-H2O (4:1). Use of 5 equiv of 2a in DMF afforded
the dihydrobenzofuran 18 in 47% yield.29
c
c
-
This work. Reference 17a. c -: not determined. Reference
a
b
d
17b.
Dihydrobenzofuran 18 can be produced via intramo-
lecular 5-exo cyclization of the aryl radical 21, derived
from the selective collapse of iodanyl radical 20. Associa-
tion of the cyclized alkyl radical 22 with Cr(II) followed
by the reaction with benzaldehyde (2a ) gives 18. The aryl
radical 21 undergoes 5-exo cyclization with the first-order
rate constant of 5.3 × 109 s-1 at 25 °C.30 The fact that
there is no formation of the uncyclized products derived
from the radical 21 clearly indicates that the association
of the radical 21 with Cr(II) yielding the corresponding
arylchromium(III) species will not be able to compete
with this rapid 5-exo cyclization.31
Use of a radical inhibitor 1,1-diphenylethylene, being
an efficient phenyl radical trap,27 showed negligible
effects on the product profiles for the coupling of 1a with
2a (compare Table 1, entries 1 and 3), which suggests
that the rate of reduction of phenyl radical with Cr(II) is
faster than that of intermolecular addition to the double
bond of 1,1-diphenylethylene. Intervention of aryl radi-
cals was firmly established by the following intramolecu-
lar radical trapping method (Scheme 11).28 Exposure of
(o-allyloxyphenyl)mesityliodonium salt 17 to CrCl2 (3
equiv) in the presence of benzaldehyde (2a ) (1 equiv) at
room temperature in DMF afforded a diastereomeric
mixture of the cyclized alcohol 18 (16%) in a ratio of 3:1
B. Alk en yl(a r yl)iod on iu m Sa lt . The chromium-
mediated alkenylation of an aldehyde 2 with alkenyl-
(aryl)iodonium salts 5 competes with the arylation. This
(27) (a) Barton, D. H. R.; Finet, J .-P.; Giannotti, C.; Halley, F. J .
Chem. Soc., Perkin Trans.
1 1987, 241. (b) Lubinkowski, J . J .;
Knapczyk, J . W.; Calderon, J . L.; Petit, L. R.; McEwen, W. E. J . Org.
Chem. 1975, 40, 3010. (c) Lubinkowski, J . J .; Arrieche, C. G.; McEwen,
W. E. J . Org. Chem. 1980, 45, 2076. (d) Weldon, D.; Holland, S.;
Scaiano, J . C. J . Org. Chem. 1996, 61, 8544.
(29) No formation of dihydrobenzofurans was observed in the
attempted radical cyclizations of 17 using tetrathiafulvalene as an
electron donor. See: Lampard, C.; Murphy, J . A.; Lewis, N. J . Chem.
Soc., Chem. Commun. 1993, 295.
(28) (a) Meijs, G. F.; Beckwith, A. L. J . J . Am. Chem. Soc. 1986,
108, 5890. (b) Molander, G. A.; Harring, L. S. J . Org. Chem. 1990, 55,
6171. (c) Curran, D. P.; Totleben, M. J . J . Am. Chem. Soc. 1992, 114,
6050.
(30) Beckwith, A. L. J .; Schiesser, C. H. Tetrahedron 1985, 41, 3925.
(31) The rate constant for association of 5-hexenyl radical with Cr(II)
is evaluated to be 4 ×107 M-1 s-1 at 25 °C in DMF-H2O. See: Kochi,
J . K.; Powers, J . W. J . Am. Chem. Soc. 1970, 92, 137.

6810 J . Org. Chem., Vol. 64, No. 18, 1999
Chen and Ochiai
Sch em e 12
Sch em e 14
1-decyne in the reaction of 5ea , 5fa , and 5ga is probably
due to the facile concerted or stepwise syn â-elimination
of the corresponding iodanyl radicals.
Sch em e 13
C. Alk yn yl(a r yl)iod on iu m Sa lt. Reaction of 1-decyn-
yl(phenyl)iodonium salt 9 with benzaldehyde (2a ) showed
high selectivity for alkynylation yielding the propargyl
alcohol 10. No formation of benzhydrol (3a ) was observed
(Table 5). Formation of a large amount of iodobenzene
also suggests the selective cleavage of alkynyl-iodine
bond of 9. Intervention of the polar transition state 30
generating an alkynyl radical may be compatible with
these experimental results. The selective generation of
1-decynyl radical from 29 (Scheme 14), however, seems
to be very difficult, because it has been shown that an
alkynyl radical is a highly energetic species, with a
stabilization energy of SE° ) -15.57 kcal/mol for
HCtC•.33,35
When Cr-mediated coupling of 9 with 2a was per-
formed in DMF-d7, GC-MS analysis showed only 7%
deuterium incorporation in the byproduct 1-decyne (12),
while in MeOD the reaction revealed 98% deuterium
incorporation at the terminal position. These results may
constitute an evidence for the generation of 1-decynyl-
chromium(III) but not for the intervention of 1-decynyl
radical. Alkynyl radicals might selectively abstract the
R-hydrogen of MeOD because the dissociation energy
(94.55 kcal/mol) of the C-H bond of methanol is smaller
than that of the O-H bond (103 kcal/mol).36 It has been
reported that photochemical decomposition of (3,3-di-
methyl-1-butynyl)(phenyl)iodonium tosylate in ethanol
generates, via a single-electron transfer, the correspond-
ing 9-I-2 iodanyl radical, which undergoes cleavage of the
phenyl-iodine bond with high selectivity and affords a
mixture of 3,3-dimethyl-1-iodo-1-butyne and iodobenzene
in a ratio of 84:16.37,38 This selectivity is quite different
from those shown in Table 5. Therefore, it seems reason-
able to assume that generation and decomposition of 9-I-2
iodanyl radical 29 to produce 1-decynyl radical is not a
significant process in the reaction of 1-decynyliodonium
salt 9 with CrCl2.
reaction also involves intervention of the [9-I-2] iodanyl
radical via a single-electron transfer form Cr(II) analo-
gous to the reaction with diaryliodonium salts 1. As
illustrated in Scheme 12, decomposition of the iodanyl
radical 25 derived from 5a could produce both the
cyclohexenyl radical 24 and an aryl radical. The former
will result in formation of allyl alcohols 6 via the reaction
with aldehydes whereas the latter will yield the alcohols
3.
It is known that a combination of the simple vinyl
radical 26 and iodobenzene is more stable than that of
phenyl radical with vinyl iodide 27 (Scheme 13).3a,32 The
stabilization energy (SE° ) -6.16 kcal/mol) of the vinyl
radical 26 is larger than that of the phenyl radical
(-10.27 kcal/mol).33 These thermochemical data would
predict a larger extent of alkenylation than phenylation
in the reaction of 5a a and 5ca with benzaldehyde (2a ),
which is contrary to the results shown in Table 3, entries
1 and 6. The polar transition state 28 (Ar ) Ph) with
partial charge separation, as was discussed for decom-
position of the unsymmetrical diaryliodanyl radicals 15,
explains the selectivity for cleavage of phenyl-iodine over
vinyl-iodine bonds of 25 (Ar ) Ph). The polar transition
state 28a (Ar ) Ph) might be energetically more favorable
than the alternative 28b (Ar ) Ph) because the negative
charge developed will be more effectively stabilized by
the phenyl group than by the vinyl group. The fact that
phenyl carbanion is slightly more stable than ethenyl
carbanion is compatible with this hypothesis,34 since
replacement of an R-hydrogen of a carbanion with an
alkyl group is known to decrease the stability. When
electron-donating groups were introduced to the aryl
moiety of 5a , the energy of the transition state 28a will
be increased, and therefore, cleavage of the vinyl-iodine
bond of 25 leading to the formation of allyl alcohol 6a
becomes more favored. The results in Table 3 (entries 2
and 3) probably reflect this substituent effect.
It has been generally accepted that one of the most
common modes of the reactions of alkynyliodonium salts
with nucleophiles involves the Michael addition to the
electron-deficient â-acetylenic carbon atom to generate
alkylidenecarbenes via reductive elimination of the hy-
perleaving group.1l,40 This Michael-carbene pathway
might account for the predominant formation of the
propargyl alcohol 10 and iodobenzene.41
Extensive cleavage of phenyl-iodine over vinyl-iodine
bonds was observed in the reaction of (E)-1-decenyl-
(phenyl)iodonium salt 5ca , whereas â-halo 5ea and 5fa
and â-benzenesulfonyl derivatives 5ga showed reversed
selectivity (Table 3, entries 6 and 9-11). These electron-
withdrawing â-substituents stabilize the negative charge
developed at the vinylic carbon in the polar transition
state, which in turn results in predominant cleavage of
the vinyl-iodine bond. Formation of a large amount of
(35) For generation of alkynyl radicals, see: (a) Kunishima, M.;
Tanaka, S.; Kono, K.; Hioki, K.; Tani, S. Tetrahedron Lett. 1995, 36,
3707. (b) Kasai, P. H.; McBay, H. C. J . Phys. Chem. 1984, 88, 5932. (c)
Inoue, Y.; Fukunaga, T.; Hakushi, T. J . Org. Chem. 1983, 48, 1732.
(36) Berkowitz, J .; Ellison, G. B.; Gutman, D. J . Phys. Chem. 1994,
98, 2744.
(37) Kitamura, T.; Tanaka, T.; Taniguchi, H. Chem. Lett. 1992, 2245.
(38) Similar selectivity for decomposition of 1-decynyl(phenyl)-
iodonium salt 9 was observed in the reduction with tetrakis(dimethyl-
amino)ethylene,39 which gave a mixture of 1-iodo-1-decyne (58%),
iodobenzene (13%), 1-decyne (12) (37%), and benzene (46%). The
reduction with triethylamine afforded a similar ratio of the products.
These reactions probably involve the intervention of 9-I-2 iodanyl
radical 29.
(32) Golden, D. M.; Benson, S. W. Chem. Rev. 1969, 69, 125.
(33) (a) Leroy, G.; Peeters, D.; Wilante, C. J . Mol. Struct., Theochem.
1982, 88, 217. (b) Wyatt, J . R.; Stafford, F. E. J . Phys. Chem. 1972,
76, 1913.
(34) Dessy, R. E.: Kitching, W.; Psarras, T.; Salinger, R.; Chen, A.;
Chivers, T. J . Am. Chem. Soc. 1966, 88, 460.
(39) Burkholder, C.; Dolbier J r., W. R.; Medebielle, M. Tetrahedron
Lett. 1997, 38, 821.

Chromium(II)-Mediated Reactions of IodoniumTetrafluoroborates
J . Org. Chem., Vol. 64, No. 18, 1999 6811
Sch em e 15
the use of both aryl moieties of diaryliodonium salts.
Studies on substituent effects in the reaction of unsym-
metrical diaryliodonium salts and intramolecular radical
trapping experiments revealed that the Cr-mediated
coupling of diaryliodonium salts with aldehydes would
involve (1) reduction of the hypervalent iodine to generate
iodanyl radical via a single-electron transfer, (2) unimo-
lecular decomposition of the iodanyl radical via a polar
transition state to produce both aryl radical and aryl
iodide, and (3) association of the aryl radical with CrCl2
to generate arylchromium(III), which reacts with alde-
hydes to give alcohols. The aryl iodide produced in situ
also generates arylchromium(III) when a Ni catalyst is
present.
In the Cr-mediated coupling of alkenyl(phenyl)iodo-
nium salts with aldehydes, alkenylation and phenylation
compete with each other; however, use of alkenyl-
(mesityl)iodonium salts gives the alkenylation product
exclusively. Similarly, alkynyl(phenyl)iodonium salts
selectively undergo alkynylation of aldehydes. This method
of using aryl-, alkenyl-, and alkynyliodonium salts as
their anion equivalents in the reaction with aldehydes
represents the first example of reactivity umpolung of
iodonium salts.
Syn th esis of Iodon iu m Salts. BF3-Catalyzed silicon-
iodine(III) exchange reaction of organosilanes with (di-
acetoxyiodo)arenes or iodosylarenes constitutes a general
method for synthesis of alkenyl(aryl)iodonium salts
(Scheme 15).3a,42 This reaction proceeds under mild
conditions and in a stereospecific manner with retention
of configuration of organosilanes. Thus, 4-tert-butyl-
cyclohexenyl(aryl)iodonium tetrafluoroborates 5a a -5a c
were prepared from 4-tert-butyl-1-(trimethylsilyl)cyclo-
hexene by reaction with iodosylarenes in the presence of
BF3‚Et2O.2,43 Similarly, reaction of 1-(trimethylsilyl)-
cyclopentene, (E)-1-(trimethylsilyl)decene, and 2-butyl-
1-(trimethylsilyl)hexene afforded 1-cyclopentenyliodoni-
um salts 5ba and 5bc, (E)-1-decenyliodonium salts 5ca
and 5cc, and 2-butyl-1-hexenyliodonium salt 5d c, re-
spectively. BF3-Catalyzed borane-iodine(III) exchange of
organoboronic acids with (diacetoxyiodo)arenes is an
efficient alternative for the synthesis of iodonium salts;44
(E)-â-styryl(mesityl)iodonium tetrafluoroborate (5h c) was
obtained by the reaction of (E)-â-styrylboronic acid with
2,4,6-trimethyl(diacetoxyiodo)benzene in the presence of
BF3‚Et2O. Symmetrical 1c and unsymmetrical diaryl-
iodonium salts 4c and 4d were prepared by the borane-
iodine(III) exchange reaction. Similarly, reaction of o-
allyloxyphenylboronic acid45 with 2,4,6-trimethyl(di-
acetoxyiodo)benzene afforded the (o-allyloxyphenyl)-
mesityliodonium salt 17.
Exp er im en ta l Section
Gen er a l Meth od s. For general experimental details, see
ref 2. Preparative thin-layer chromatography (TLC) was
carried out on precoated plates of silica gel (Merck, silica gel
F-254). Kieselgel 60 (Merck, 230-400 mesh) was used for flash
chromatography. Anhydrous chromium dichloride was pur-
chased form Kishida Chemical Co. The color should be gray.
Any green color means low purity. Handling of this reagent
must be carried out in drybox under nitrogen.
Con clu sion s
We have demonstrated that diaryliodonium salts react
with CrCl2 in DMF at room temperature to generate
arylchromiun(III) species, which efficiently add to a
variety of aldehydes to produce alcohols in good yields.
In marked contrast to the reaction of aryl halides with
CrCl2, the activation of diaryliodonium salts by a nickel
catalyst is not required in this reaction, probably because
of the highly electron-deficient nature of these salts.
Addition of a catalytic amount of NiCl2 makes possible
Syn th esis of Iodon iu m Tetr aflu or obor ates via Silicon -
Iod in e(III) Exch a n ge. A Rep r esen ta tive Exa m p le. (4-ter t-
Bu t yl-1-cycloh exen yl)(2,4,6-t r im et h ylp h en yl)iod on iu m
Tet r a flu or obor a t e (5a c). To a stirred solution of iodosyl-
mesitylene46 (1.05 g, 4.0 mmol) and 4-tert-butyl-1-(trimethyl-
silyl)cyclohexene (840 mg, 4.0 mmol) in dichloromethane (30
mL) was added BF3‚Et2O (570 mg, 4.0 mmol) at 0 °C in
nitrogen, and the mixture was stirred for 1 h at 0 °C and for
17 h at room temperature. After addition of a saturated
aqueous sodium tetrafluoroborate (80 mmol) solution, the
mixture was stirred for 30 min. The reaction mixture was
poured into water and extracted with dichloromethane. The
organic layer was concentrated under aspirator vacuum to give
an oil, which was washed several times with hexane-diethyl
ether by decantation at -78 °C. Recrystallization from hex-
ane-dichloromethane gave the vinyliodonium salt 5a c (707
mg, 38%) as a colorless powder: mp 113-114 °C; IR (CHCl3)
(40) (a) Ochiai, M.; Kunishima, M.; Nagao, Y.; Fuji, K.; Shiro, M.;
Fujita, E. J . Am. Chem. Soc. 1986, 108, 8281. (b) Ochiai, M.;
Kunishima, M.; Tani, S.; Nagao, Y. J . Am. Chem. Soc. 1991, 113, 3135.
(41) There is no available data on the nucleophilicity of CrCl2 and
no evidence supporting this mechanism, but intervention of alkynyl-
chromium(IV) species have been proposed in the reaction of alkynyl
iodides with CrCl2.19 Generation of R-chromium(III) alkylidenecarbenes
by the reaction of 9 with 2 molar equiv of CrCl2 via a single-electron
transfer is a possible alternative.
1217, 1029, 774, 670 cm-1 1H NMR (CDCl3) δ 7.13 (s, 2H),
;
6.73 (m, 1H), 2.61 (s, 6H), 2.60-2.10 (m, 3H), 2.38 (s, 3H),
2.00-1.88 (m, 1H), 1.70-1.30 (m, 3H), 0.84 (s, 9H); FAB MS
m/z 383 [(M - BF4)+]. Anal. Calcd for C19H28BF4I: C, 48.54;
H, 6.00. Found: C, 48.28; H, 5.92.
(1-Cyclopen ten yl)(2,4,6-tr im eth ylph en yl)iodon iu m tet-
r a flu or obor a te (5bc): 25%; pale brown crystals; mp 110-
111 °C (recrystallized from hexane-dichloromethane); IR (CHCl3)
1
1216, 1063, 1024, 765, 670 cm-1; H NMR (CDCl3) δ 7.12 (s,
2H), 6.70 (br s, 1H), 2.75-2.55 (4H), 2.62 (s, 6H), 2.37 (s, 3H),
2.05 (quint, J ) 7.5 Hz, 2H); HRMS (FAB) calcd for C14H18
I
[(M - BF4)+] 313.0453, found 313.0432.
(E)-(1-Decen yl)(2,4,6-t r im et h ylp h en yl)iod on iu m t et -
r a flu or obor a te (5cc): 42%; colorless amorphous solids; IR
(42) Ochiai, M.; Sumi, K.; Nagao, Y.; Shiro, M.; Fujita, E. Tetrahe-
dron Lett. 1985, 26, 2351.
(43) Ochiai, M.; Shu, T.; Nagaoka, T.; Kitagawa, Y. J . Org. Chem.
1997, 62, 2130.
1
(CHCl3) 1216, 1063, 1024, 769, 670 cm-1; H NMR (CDCl3) δ
(44) Ochiai, M.; Toyonari, M.; Nagaoka, T.; Chen, D.-W.; Kida, M.
Tetrahedron Lett. 1997, 38, 6709.
(45) Morgan, J .; Pinhey, J . T. J . Chem. Soc., Perkin Trans. 1 1993,
1673.
(46) For preparation of (diacetoxyiodo)arenes and iodosylarenes,
see: Ochiai, M.; Ito, T.; Takaoka, Y.; Masaki, Y. J . Am. Chem. Soc.
1991, 113, 1319.

6812 J . Org. Chem., Vol. 64, No. 18, 1999
Chen and Ochiai
7.13 (s, 2H), 6.56 (d, J ) 13.7 Hz, 1H), 6.35 (dt, J ) 13.7, 6.8
Hz 1H), 2.61 (s, 6H), 2.37(s, 3H), 2.25 (q, J ) 6.8 Hz, 2H),
1.45-1.15 (m, 12H), 0.87 (t, J ) 6.4 Hz, 3H); HRMS (FAB)
calcd for C19H30I [(M - BF4)+] 385.1392, found 385.1418.
(2-Bu tyl-1-h exen yl)(2,4,6-tr im eth ylph en yl)iodon iu m tet-
r a flu or obor a te (5d c): 55%; colorless needles; mp 67-68 °C
(recrystallized from hexane-dichloromethane); IR (CHCl3)
according to the procedure developed by Beringer.48 4b:
colorless needles; mp 209-210 °C (recrystallized from hexane-
dichloromethane); IR (CHCl3) 1216, 1075, 1031, 778, 744, 670
cm-1; 1H NMR (CDCl3) δ 7.69 (br d, J ) 7.5 Hz, 2H), 7.54 (br
t, J ) 7.5 Hz, 1H), 7.42 (br t, J ) 7.5 Hz, 2H), 7.12 (s, 2H),
2.64 (s, 6H), 2.36 (s, 3H); FAB MS m/z 323 [(M - BF4)+]. Anal.
Calcd for C15H16BF4I: C, 43.94; H, 3.93. Found: C, 43.93; H,
3.94.
(4-Methoxyphenyl)phenyliodonium tetrafluoroborate (4a )49
was prepared in a similar manner. Bis(4-chlorophenyl)iodo-
nium tetrafluoroborate (1b)47 was prepared by coupling of
chlorobenzene with iodyl sulfate in sulfuric acid.50 Michael
addition of acids to 1-decynyl(phenyl)iodonium tetrafluoro-
borate (9)51 gave â-chloro- 5ea ,52 â-bromo- 5fa ,52 and â-(phen-
ylsulfonyl)vinyliodonium tetrafluoroborates 5ga 40b in good
yields.
Gen er a l P r oced u r e for Ch r om iu m -Med ia ted Ar yla tion
of Ald eh yd es 2 w ith Dia r yliod on iu m Tetr a flu or obor a tes
1. To a stirred emerald green solution of anhydrous CrCl2 (148
mg, 1.2 mmol) and NiCl2 (0.8 mg, 0.006 mmol) in dry DMF (4
mL) was added a solution of an diaryliodonium tetrafluoro-
borate 1 (0.3 mmol) and an aldehyde 2 (0.3 mmol) in DMF (1
mL) under argon at room temperature, and the solution was
stirred for 5 h. The reaction mixture was quenched with water
and extracted with diethyl ether. The combined organic
extracts were washed with water and brine. The organic layer
was filtered and dried over anhydrous sodium sulfate. The
yields of arenes and iodoarenes were determined by analytical
GC (decane or tetradecane as the internal standard). Purifica-
tion with preparative TLC (hexane-ethyl acetate) gave pure
products 3. The yields of pure products are given in Table 1.
Dip h en ylm eth a n ol (3a ): colorless prisms; mp 69 °C (re-
crystallized from dichloromethane-hexane, lit.53 mp 69 °C);
1H NMR (CDCl3) δ 7.42-7.2 (m, 10H), 5.85 (s, 1H), 2.25 (s,
1H).
1
1215, 780, 741 cm-1; H NMR (CDCl3) δ 7.10 (s, 2H), 6.18 (s,
1H), 2.63 (s, 6H), 2.45-2.30 (7H), 1.55-1.20 (m, 8H), 0.97-
0.83 (6H); HRMS (FAB) calcd for
C
19H30I [(M - BF4)+]
385.1392, found 385.1386. Anal. Calcd for C19H30BF4I‚1/2H2O:
C, 47.42; H, 6.49. Found: C, 47.45; H, 6.26.
(4-tert-Butyl-1-cyclohexenyl)phenyliodonium tetrafluoro-
borate (5a a ),2 (4-tert-butyl-1-cyclohexenyl)(p-methoxyphenyl)-
iodonium tetrafluoroborate (5a b),3g (1-cyclopentenyl)phenyl-
iodonium tetrafluoroborate (5b a ),3g and (E)-(1-decenyl)-
phenyliodonium tetrafluoroborate (5ca )3b were prepared simi-
larly by the silicon-iodine(III) exchange reaction.
Syn th esis of Iod on iu m Tetr a flu or obor a tes via Bo-
r a n e-Iod in e(III) Exch a n ge. A Rep r esen ta tive Exa m p le.
(2-(2-P r op en yloxy)p h en yl)(2,4,6-t r im et h ylp h en yl)iod o-
n iu m Tetr a flu or obor a te (17). To a stirred mixture of
o-allyloxyphenyl boronic acid45 (187 mg, 1.05 mmol) and BF3‚
Et2O (156 mg, 1.10 mmol) in dichloromethane (10 mL) was
added a solution of 2,4,6-trimethyl(diacetoxyiodo)benzene46
(364 mg, 1.0 mmol) in dichloromethane (10 mL) at 0 °C in
nitrogen, and the mixture was stirred for 1.5 h at 0 °C. After
the addition of a saturated aqueous sodium tetrafluoroborate
(20 mmol) solution, the mixture was stirred for 30 min. The
reaction mixture was poured into water and extracted with
dichloromethane. The organic layer was concentrated under
aspirator vacuum to give a solid residue, which was washed
several times with diethyl ether by decantation at -78 °C.
Recrystallization from diethyl ether-dichloromethane gave the
vinyliodonium salt 17 (407 mg, 87%) as pale yellow crystals:
mp 168-170 °C; IR (CHCl3) 1216, 1024, 759, 670 cm-1 1H
;
(4-Ch lor oph en yl)ph en ylm eth an ol (3b): colorless needles;
mp 59-61 °C (recrystallized from dichloromethane-hexane,
NMR (CDCl3) δ 7.54 (br t, J ) 7.7 Hz, 1H), 7.17 (s, 2H), 7.16-
6.93 (m, 3H), 6.12-5.90 (m, 1H), 5.45-5.33 (2H), 4.77 (d, J )
7.7 Hz, 2H), 2.60 (s, 6H), 2.39 (s, 3H); HRMS (FAB) calcd for
1
lit.54 mp 59 °C); H NMR (CDCl3) δ 7.40-7.27 (m, 9H), 5.81
(s, 1H), 2.24 (br s, 1H); HRMS calcd for C13H11ClO (M+)
218.0498, found 218.0501.
C
18H20IO [(M - BF4)+] 379.0559, found 379.0544. Anal. Calcd
for C18H20BF4IO: C, 46.39; H, 4.33. Found: C, 46.09; H, 4.24.
(4-Meth ylp h en yl)p h en yliod on iu m tetr a flu or obor a te
(4c): 83%; pale brown prisms; mp 128-129 °C (recrystallized
from hexane-dichloromethane); IR (CHCl3) 1218, 1067, 1026,
774, 668 cm-1; 1H NMR (CDCl3) δ 8.00 (br d, J ) 7.5 Hz, 2H),
7.92 (d, J ) 8.5 Hz, 2H), 7.61 (br t, J ) 7.5 Hz, 1H), 7.45 (br
t, J ) 7.5 Hz, 2H), 7.27 (d, J ) 8.5 Hz, 2H), 2.40 (s, 3H); FAB
MS m/z 295 [(M - BF4)+]. Anal. Calcd for C13H12BF4I: C, 40.88;
H, 3.17. Found: C, 41.02; H, 3.16.
(4-Meth ylp h en y)p h en ylm eth a n ol (3c): colorless needles;
mp 52 °C (recrystallized from dichloromethane-hexane, lit.55
mp 52-53 °C); 1H NMR (CDCl3) δ 7.40-7.10 (9H), 5.80 (s, 1H),
2.32 (s, 3H), 2.20 (br s, 1H); HRMS calcd for C14H14O (M+)
198.1045, found 198.1036.
(4-Meth oxyp h en yl)p h en ylm eth a n ol (3d ):56 mp 95 °C
(recrystallized from dichloromethane-hexane); 1H NMR (CDCl3)
δ 7.40-7.21 (m, 7H), 6.86 (d, J ) 7.8 Hz, 2H), 5.80 (br s, 1H),
3.78 (s, 3H), 2.20 (br s, 1H); HRMS calcd for C14H14O2 (M+)
214.0994, found 214.0982.
(4-Ch lor op h en yl)p h en yliod on iu m tetr a flu or obor a te
(4d ): 73%; colorless crystals; mp 113-115 °C (recrystallized
from hexane-dichloromethane); IR (CHCl3) 1216, 1070, 1028,
759, 670 cm-1; 1H NMR (CDCl3) δ 8.04 (br d, J ) 7.5 Hz, 2H),
7.98 (br d, J ) 8.8 Hz, 2H), 7.62 (br t, J ) 7.5 Hz, 1H), 7.48-
7.32 (4H); FAB MS m/z 315 [(M - BF4)+]. Anal. Calcd for
(2-Meth ylp h en yl)p h en ylm eth a n ol (3e): colorless prisms;
mp 95 °C (recrystallized from dichloromethane-hexane, lit.57
1
mp 95 °C); H NMR (CDCl3) δ 7.56-7.49 (m, 1H), 7.37-7.09
(m, 8H), 6.00 (br s, 1H), 2.25 (s, 3H), 2.13 (1H); HRMS calcd
for C14H14O (M+) 198.1045, found 198.1042.
C
12H9BClF4I: C, 35.82; H, 2.25. Found C, 35.75; H, 2.34.
(E)-(â-Styr yl)(2,4,6-tr im eth ylph en yl)iodon iu m tetr aflu -
or obor a te (5h c): 59%; pale brown prisms; mp 177-178 °C
(recrystallized from hexane-dichloromethane); IR (CHCl3)
1216, 1030, 770, 670 cm-1; 1H NMR (CDCl3) δ 7.40-7.10 (9H),
2.66 (s, 6H), 2.39 (s, 3H); FAB MS m/z 349 [(M - BF4)+]. Anal.
Calcd for C17H18BF4I: C, 46.83; H, 4.16. Found: C, 46.82; H,
4.12.
(48) Beringer, F. M.; Drexler, M.; Gindler, M.; Lumpkin, C. C. J .
Am. Chem. Soc. 1953, 75, 2705.
(49) Caserio, M. C.; Glusker, D. L.; Roberts, J . D. J . Am. Chem. Soc.
1959, 81, 336.
(50) Beringer, F. M.; Falk, R. A.; Karniol, M.; Lillien, I.; Masullo,
G.; Mausner, M.; Sommer, E. J . Am. Chem. Soc. 1959, 81, 342.
(51) (a) Ochiai, M.; Kunishima, M.; Sumi, K.; Nagao, Y.; Fujita, E.
Tetrahedron Lett. 1985, 26, 4501. (b) Ochiai, M.; Kunishima, M.; Nagao,
Y.; Fuji, K.; Fujita, E. J . Chem. Soc., Chem. Commun. 1987, 1708.
(52) Ochiai, M.; Uemura, K.; Oshima, K.; Masaki, Y.; Kunishima,
M.; Tani, S. Tetrahedron Lett. 1991, 32, 4753.
(53) Wiselogle, F. Y.; Sonneborn, H. Organic Syntheses; Wiley: New
York, 1941; Collect. Vol. I, p 90.
(54) Bachman, W. E.; Carlson, E.; Moran, J . C. J . Org. Chem. 1948,
13, 916.
(55) Davies, A. G.; Kenyon, J .; Lyons, B. J .; Rohan, J . A. J . Chem.
Soc. 1954, 3474.
Bis(4-methylphenyl)iodonium tetrafluoroborate (1c)47 was
prepared similarly in 83% yield by the borane-iodine(III)
exchange reaction.
Syn th esis of P h en yl(2,4,6-tr im eth ylp h en yl)iod on iu m
Tetr a flu or obor a te (4b). The unsymmetrical diaryliodonium
salt 4b was prepared in 84% yield by Friedel-Crafts-type
condensation between (diacetoxyiodo)benzene and mesitylene
in acetic acid-acetic anhydride in the presence of sulfuric acid,
(56) Bouquet, M.; Guy, A.; Lemaite, M.; Guette, J . P. Synth.
Commun. 1985, 15, 1153.
(57) Roos, A. M. Recl. Trav. Chim Pays-Bas 1968, 87, 1381.
(47) Reutov, O. A.; Ertel, G. A.; Ptitsina, O. A. Dokl. Akad. Nauk
SSSR 1960, 133, 1108.

Chromium(II)-Mediated Reactions of IodoniumTetrafluoroborates
J . Org. Chem., Vol. 64, No. 18, 1999 6813
1-P h en yl-1-u n decan ol (3f):58 colorless oil; 1H NMR (CDCl3)
δ 7.36-7.26 (m, 5H), 4.66 (t, J ) 6.8 Hz, 1H), 1.85-1.70 (m,
3H), 1.25 (m, 16H), 0.88 (t, J ) 6.5 Hz, 3H); HRMS calcd for
1-(Hyd r oxy(p h en yl)m eth yl)-1-cyclop en ten e (6b):64 col-
orless oil; H NMR (CDCl3) δ 7.40-7.24 (m, 5H), 5.69 (br s,
1
1H), 5.33 (s, 1H), 2.40-2.15 (m, 5H), 1.98-1.78 (m, 2H).
(E)-1-P h en yl-2-u n d ecen -1-ol (6c): 1H NMR (CDCl3) δ
7.44-7.20 (m, 5H), 5.78 (dt, J ) 15.0, 6.9 Hz, 1H), 5.66 (dd, J
) 15.0, 6.2 Hz, 1H), 5.18 (d, J ) 6.2 Hz, 1H), 2.12-2.0 (m,
2H), 1.90-1.80 (1H), 1.45-1.20 (12H), 0.88 (t, J ) 6.6 Hz, 3H);
MS m/z (relative intensity) 246 (53, M+), 133 (100), 120 (76),
105 (58); HRMS calcd for C17H26O (M+) 246.1984, found
246.1952. The alcohol 6c was contaminated with a small
amount of impurities.
C
17H28O (M+) 248.2140, found 248.2130.
2-Meth yl-1-p h en yl-1-p r op a n ol (3g):59 colorless oil; 1H
NMR (CDCl3) δ 7.40-7.20 (m, 5H), 4.36 (d, J ) 6.6 Hz, 1H),
1.96 (octet, J ) 6.6 Hz, 1H), 1.88 (br s, 1H), 1.00 (d, J ) 6.6
Hz, 3H), 0.80 (d, J ) 6.6 Hz, 3H); HRMS calcd for C10H14
O
(M+) 150.1045, found 150.1038.
(E)-1-P h en yl-2-bu ten -1-ol (3i):60 colorless oil; 1H NMR
(CDCl3) δ 7.41-7.20 (m, 5H), 5.88-5.60 (m, 2H), 5.15 (d, J )
5.1 Hz, 1H), 1.87 (br s, 1H), 1.72 (d, J ) 5.1 Hz, 3H); HRMS
calcd for C10H12O (M+) 148.0888, found 148.0892.
(E)-1,3-Dip h en yl-2-p r op en -1-ol (3j):61 colorless oil; 1H
NMR (CDCl3) δ 7.48-7.19 (m, 10H), 6.69 (d, J ) 16 Hz, 1H),
6.38 (dd, J ) 16, 6.4 Hz, 1H), 5.38 (d, J ) 6.4 Hz, 1H), 2.1 (br
s, 1H); HRMS calcd for C15H14O (M+) 210.1045, found 210.0974.
3-Bu tyl-1-p h en yl-2-h ep ten -1-ol (6d ): colorless oil; IR
(CHCl3) 3600, 1660 cm-1 1H NMR (CDCl3) δ 7.41-7.21 (m,
;
5H), 5.49 (d, J ) 8.6 Hz, 1H), 5.39 (d, J ) 8.6 Hz, 1H), 2.25-
2.10 (m, 2H), 2.10-1.95 (m, 2H), 1.70 (s, 1H), 1.52-1.17 (m,
8H), 0.92 (t, J ) 6.6 Hz, 3H), 0.89 (t, J ) 6.6 Hz, 3H); MS m/z
(relative intensity) 246 (6, M+),189 (100), 129 (11); HRMS calcd
for C17H26O (M+) 246.1984, found 246.1983.
(Z)-1-P h en yl-3-p h en ylsu lfon yl-2-u n cecen -1-ol (6g): col-
orless oil; IR (CHCl3) 3590, 1305, 1152, 780, 700 cm-1; 1H NMR
(CDCl3) δ 7.9-7.8 (m, 2H), 7.65-7.48 (m, 3H), 7.38 (5H), 7.08
(d, J ) 7.5 Hz, 1H), 5.45 (d, J ) 7.5 Hz, 1H), 2.41-2.2 (m,
2H), 2.10 (br s, 1H), 1.45-1.0 (12H), 0.87 (t, J ) 6.6 Hz, 3H);
MS m/z (relative intensity) 386 (2, M+), 281 (70), 245 (100),
143 (90), 107 (100), 79 (80); HRMS calcd. for C23H30O3S (M+)
386.1916, found 386.1943.
4-ter t-Bu tyl-1-(h yd r oxy(4-ch lor op h en yl)m eth yl)-1-cy-
cloh exen e (6i): a 6:4 mixture of diastereoisomers; colorless
oil; IR (CHCl3) 3600, 1380, 1100 cm-1; 1H NMR (CDCl3) δ 7.29
(s, 4H), 5.84 (m, 1H), 5.10 (s, 0.4H), 5.07 (s, 0.6H), 2.23-1.95
(m, 1H), 1.95-1.70 (m, 5H), 1.34-1.0 (m, 2H), 0.85 (s, 9H);
MS m/z (relative intensity) 278 (55, M+), 203 (49), 139 (100);
HRMS calcd for C17H23ClO (M+) 278.1437, found 278.1424.
4-ter t-Bu tyl-1-(h yd r oxy(4-m eth ylp h en yl)m eth yl)-1-cy-
cloh exen e (6j): a 6:4 mixture of diastereoisomers; colorless
oil; IR (CHCl3) 3600 cm-1; 1H NMR (CDCl3) δ 7.25-7.10 (4H),
5.84 (m, 1H), 5.07 (s, 0.4H), 5.04 (s, 0.6H), 2.34 (s, 3H), 2.22-
1.98 (m, 1H), 1.95-1.70 (m, 5H), 1.34-1.0 (m, 2H), 0.85 (s,
9H); MS m/z (relative intensity) 258 (55, M+), 243 (51), 134
(40), 119 (100); HRMS calcd for C18H26O (M+) 258.1984, found
258.1978.
4-ter t-Bu tyl-1-(1-h yd r oxy-2-m eth ylp r op yl)-1-cycloh ex-
en e (6k ): a 6:4 mixture of diastereoisomers; colorless oil; IR
(CHCl3) 3600, 1370, 1005 cm-1; 1H NMR (CDCl3) δ 5.76-5.58
(1H), 3.63 (d, J ) 6.8 Hz, a minor isomer), 3.57 (d, J ) 7.5 Hz,
a major isomer), 2.30-1.04 (m, 9H), 1.0 (d, J ) 6.8 Hz, a major
isomer), 0.95 (d, J ) 6.8 Hz, a minor isomer), 0.89 (s, 9H),
0.83 (d, J ) 6.8 Hz, a minor isomer), 0.80 (d, J ) 6.8 Hz, a
major isomer); MS m/z (relative intensity) 210 (7, M+), 192
(37), 167 (100), 135 (95); HRMS calcd for C14H26O (M+)
210.1984, found 210.1975.
Ch r om iu m -Med ia ted Cou p lin g of Hexa n oyl Ch lor id e
w ith Dip h en yliod on iu m Tetr a flu or obor a te (1a ). To a
stirred solution of CrCl2 (83 mg, 0.67 mmol) doped with NiCl2
(0.5 mol %) in dry DMF (2 mL) was added a solution of
diphenyliodonium tetrafluoroborate (1a ) (62 mg, 0.17 mmol)
and hexanoyl chloride (23 mg, 0.17 mmol) in DMF (0.5 mL)
under argon at room temperature, and the solution was stirred
for 5 h. The reaction mixture was quenched with water and
extracted with diethyl ether. The combined organic extracts
were washed with water and brine. The organic layer was
filtered, dried over anhydrous sodium sulfate, and concen-
trated to give an oil, which was purified by preparative TLC
(hexane-ethyl acetate (10:1)) to give hexanophenone (6.7 mg,
23%), benzophenone (1.3 mg, 4%), benzhydrol (3a ) (2.4 mg,
8%), and N,N-dimethylhexanamide (2.2 mg, 9%). Hexanophe-
none: colorless oil; 1H NMR (CDCl3) δ 7.96 (d, J ) 7 Hz, 2H),
7.60-7.40 (m, 3H), 2.97 (t, J ) 7.6 Hz, 2H), 1.75 (m, 2H), 1.36
(m, 4H), 0.91 (t, J ) 6.6 Hz, 3H). N,N-Dimethylhexanamide:
colorless oil; 1H NMR (CDCl3) δ 3.01 (s, 3H), 2.94 (s, 3H), 2.31
(t, J ) 7.3 Hz, 2H), 1.63 (m, 2H), 1.32 (m, 4H), 0.90 (t, J ) 6.5
Hz, 3H).
Rep r esen ta tive P r oced u r e for Ch r om iu m -Med ia ted
Cou p lin g of Ald eh yd es 2 w ith Alk en yl(a r yl)iod on iu m
Tetr a flu or obor a tes 5 (Ta ble 3, En tr y 1). To a stirred
emerald green solution of anhydrous CrCl2 (47 mg, 0.38 mmol)
in dry DMF (1 mL) was added a solution of 4-tert-butylcyclo-
hexenyl(phenyl)iodonium tetrafluoroborate (5a a ) (46 mg, 0.09
mmol) and benzaldehyde (2a ) (10 mg, 0.09 mmol) in DMF (0.3
mL) under argon at room temperature, and the solution was
stirred for 5 h. The reaction mixture was quenched with water
and extracted with diethyl ether. The combined organic
extracts were washed with water and brine. The organic layer
was filtered and dried over anhydrous sodium sulfate. The
yield (39%) of iodobenzene was determined by analytical GC
(tetradecane as the internal standard). Purification with
preparative TLC (hexane-ethyl acetate (10:1)) gave a diaster-
eomeric mixture (6:4) of 4-tert-butyl-1-(hydroxy(phenyl)-
methyl)-1-cyclohexene (6a ) (8.1 mg, 35%) as a colorless oil,
benzhydrol (3a ) (7.4 mg, 43%), and 4-tert-butyl-1-iodo-1-
cyclohexene (7a ) (15.1 mg, 61%). 6a :62 IR (CHCl3) 3575, 1360
(E)-4-ter t-Bu t yl-1-(1-h yd r oxy-2-b u t en yl)-1-cycloh ex-
1
en e (6l): colorless oil; IR (CHCl3) 3600, 1370, 980 cm-1; H
NMR (CDCl3) δ 5.80-5.43 (m, 3H), 4.45 (d, J ) 6.8 Hz,1H),
2.22-1.75 (m, 5H), 1.72 (d, J ) 6.5 Hz, 3H), 1.34-1.0 (m, 2H),
0.87 (s, 9H); MS m/z (relative intensity) 208 (78, M+), 193 (60),
151 (93), 133 (98), 91 (96), 69 (100); HRMS calcd for C14H24
O
(M+) 208.1827, found 208.1834.
4-t er t -B u t y l-1-(1-h y d r o x y d e c a n y l)-1-c y c lo h e x e n e
cm-1 1H NMR (CDCl3) δ 7.40-7.26 (m, 5H), 5.89-5.84 (m,
;
1
(6m ): colorless oil; IR (CHCl3) 1380 cm-1; H NMR (CDCl3)
1H), 5.14 (s, 0.4H), 5.09 (s, 0.6H), 2.26-2.0 (m, 1H), 1.95-
1.70 (m, 4H), 1.56 (s, 1H), 1.34-1.0 (m, 2H), 0.85 (s, 9H); MS
m/z (relative intensity) 244 (100, M+), 187 (15), 105 (98); HRMS
calcd for C17H24O (M+) 244.1827, found 244.1810. 7a :63 1H
NMR (CDCl3) δ 6.37-6.28 (m, 1H), 2.60-2.48 (m, 2H) 2.2-
1.2 (m, 5H), 0.85 (s, 9H).
δ 5.63 (m, 1H), 3.97 (t, J ) 6 Hz, 1H), 2.30-1.10 (m, 24H),
0.87 (12H); MS m/z (relative intensity) 294 (27, M+), 167 (100),
149 (57), 123 (25), 93 (31); HRMS calcd for C20H38O (M+)
294.2923, found 294.2922.
(E)-1-Iod o-1-d ecen e (7c):3b 1H NMR (CDCl3) δ 6.51 (dt, J
) 14.4, 7.1 Hz, 1H), 5.97 (d, J ) 14.4 Hz, 1H), 2.05 (q, J ) 7.1
Hz, 2H), 1.50-1.15 (m, 12H), 0.88 (t, J ) 6.6 Hz, 3H).
1-Iod o-2-bu tyl-1-h exen e (7d ): 1H NMR (CDCl3) δ 5.85 (s,
1H), 2.25-2.12 (m, 4H), 1.50-1.20 (m, 8H), 0.95 (t, J ) 6.6
Hz, 3H), 0.90 (t, J ) 6.6 Hz, 3H).
(58) Man, L. T. Bull. Soc. Chim. Fr. 1966, 652.
(59) Yamamoto, K.; Hayashi, T.; Kumada, M. Bull. Chem. Soc. J pn.
1974, 47, 1555.
(60) Raotenstrauch, V.; Buchi, G.; Wuest, H. J . Am. Chem. Soc.
1974, 96, 2576.
(61) Lutz, R. E.; Weiss, J . O. J . Am. Chem. Soc. 1955, 77, 1814.
(62) Charpentier-Morize, M.; Sanaoulet, J . Bull. Soc. Chim. Fr.
1977, 331.
(Z)-2-Ch lor o-1-iod o-1-d ecen e (7e):3e 1H NMR (CDCl3) δ
6.41 (s, 1H), 2.49 (t, J ) 7.3 Hz, 2H), 1.64-1.19 (m, 12H), 0.88
(t, J ) 6.5 Hz, 3H).
(63) Pross, A.; Sternhell, S. Aust. J . Chem. 1970, 23, 989.
(64) Neuman, H.; Seebach, D. Chem. Ber. 1978, 111, 2785.

6814 J . Org. Chem., Vol. 64, No. 18, 1999
Chen and Ochiai
(Z)-2-Br om o-1-iod o-1-d ecen e (7f):3e 1H NMR (CDCl3) δ
6.82 (s, 1H), 2.57 (t, J ) 7.3 Hz, 2H), 1.64-1.20 (m, 12H), 0.88
(t, J ) 6.6 Hz, 3H).
Allyloxyp h en yl)m esityliod on iu m Sa lt 17. To a stirred
solution of CrCl2 (45 mg, 0.36 mmol) in DMF (1.5 mL) was
added a solution of (o-allyloxyphenyl)mesityliodonium salt 17
(43 mg, 0.09 mmol) and benzaldehyde (2a ) (10 mg, 0.09 mmol)
in DMF (1 mL) under argon at room temperature, and the
solution was stirred for 12 h. The reaction mixture was
quenched with water and extracted with diethyl ether. The
combined organic extracts were washed with water and brine.
The organic layer was filtered, dried over anhydrous sodium
sulfate, and concentrated to give an oil, which was purified
by preparative TLC (hexane-ethyl acetate (5:1)) to give a
diastereomeric mixture (3:1) of the cyclized alcohol 18 (3.4 mg,
16%), 3-methyl-2,3-dihydrobenzofuran (19) (1.1 mg, 9%),28a
iodomesitylene (14.1 mg, 63%%), and o-(allyloxy)iodobenzene
(2 mg, 8%). 3-(2-Hydroxy-2-phenylethyl)-2,3-dihydrobenzo-
furan (18): colorless oil; IR (CDCl3) 3575, 1595, 1480, 1010
(E)-4-ter t-Bu t yl-1-(3-h yd r oxy-1-b u t en yl)-1-cycloh ex-
1
en e (8): colorless oil; IR (CHCl3) 2940, 1370 cm-1; H NMR
(CDCl3) δ 6.20 (d, J ) 16 Hz, 1H), 5.76 (m, 1H), 5.58 (dd, J )
16, 6.6 Hz, 1H), 4.35 (m, 1H), 2.40-1.80 (m, 5H), 1.4-1.05
(m, 2H), 1.30 (d, J ) 6.4 Hz, 3H), 0.88 (s, 9H); MS m/z (relative
intensity) 208 (19, M+), 190 (40), 133 (100); HRMS calcd for
C
14H24O (M+) 208.1827, found 208.1823.
Rep r esen ta tive P r oced u r e for Ch r om iu m -Med ia ted
Cou p lin g of Ald eh yd e 2a w ith 1-Decyn yl(p h en yl)iod o-
n iu m Tetr a flu or obor a te (9) (Ta ble 5, En tr y 2). To a stirred
emerald green solution of CrCl2 (148 mg, 1.2 mmol) in dry
DMF (3 mL) was added a solution of 1-decynyliodonium
tetrafluoroborate 9 (256 mg, 0.6 mmol) and benzaldehyde (2a )
(32 mg, 0.3 mmol) in DMF (1 mL) under argon at room
temperature, and the solution was stirred for 5 h. The reaction
mixture was quenched with water and extracted with diethyl
ether. The combined organic extracts were washed with water
and brine. The organic layer was filtered and dried over
anhydrous sodium sulfate. The yield (31%) of 1-decyne (12)
was determined by analytical GC (tetradecane as the internal
standard). Purification with preparative TLC (hexane-ethyl
acetate (10:1)) gave 1-phenyl-2-undecyn-1-ol (10) (46 mg, 63%)
and 1-phenyl-2-undecyn-1-one (11) (4.5 mg, 6%). 10: colorless
oil; IR (CHCl3) 3575, 2200, 1640, 1270 cm-1; 1H NMR (CDCl3)
δ 7.60-7.50 (m, 2H), 7.45-7.25 (m, 3H), 5.48 (br s, 1H), 2.28
(dt, J ) 1.5, 7.5 Hz, 2H), 2.11 (1H) 1.65-1.16 (m, 12H), 0.90
(t, J ) 6.5 Hz, 3H); MS m/z (relative intensity) 244 (100, M+),
145 (66), 105 (71), 77 (56); HRMS calcd for C17H24O (M+)
244.1827, found 244.1813. 11: colorless oil; IR (CHCl3) 2190,
1
cm-1; H NMR (CDCl3) δ 7.40-7.26 (m, 5H), 7.22-7.09 (2H),
6.88-6.85 (1H), 6.81-6.77 (1H), 4.87 (dd, J ) 8.8, 4.9 Hz,
0.75H), 4.82 (dd, J ) 8.3, 4.4 Hz, 0.25H), 4.69 (t, J ) 8.8 Hz,
0.75H), 4.60 (t, J ) 8.8 Hz, 0.25H), 4.30-4.23 (1H), 3.72-3.63
(m, 0.25H), 3.63-3.54 (m, 0.75H), 2.36-1.92 (2H); 13C NMR
(CDCl3) δ; 159.82, 144.34, 130.51, 128.72, 128.26, 128.20,
127.96, 127.91, 125.74, 125.68, 124.36, 124.12, 120.48, 120.34,
109.61, 109.53, 77.67, 76.85, 73.48, 72.75, 44.07, 39.74, 38.66;
MS m/z (relative intensity) 240 (50, M+), 209 (78), 119 (88),
91 (100), 77 (52); HRMS calcd for C16H16O2 (M+) 240.1150,
found 240.1132. 19:28a 1H NMR (CDCl3) δ 7.20-7.08 (2H), 6.87
(t, J ) 7.1 Hz, 1H), 6.79 (d, J ) 7.9 Hz, 1H), 4.68 (t, J ) 8.5
Hz, 1H), 4.07 (t, J ) 8.5 Hz, 1H), 3.65-3.45 (m, 1H), 1.33 (d,
J ) 6.8 Hz, 3H).
GC-MS An a lysis of 1-Decyn e (12) in th e Rea ction of
Ald eh yd e 2a w ith 1-Decyn yl(p h en yl)iod on iu m Sa lt 9 in
MeOD. To a stirred suspension of CrCl2 (74 mg, 0.6 mmol)
doped with NiCl2 (0.5 mol %) in dry MeOD (1 mL) was added
a solution of 1-decynyliodonium tetrafluoroborate 9 (128 mg,
0.3 mmol) and benzaldehyde (2a ) (32 mg, 0.3 mmol) in MeOD
(2 mL) under argon at room temperature, and the solution was
stirred for 30 h. The reaction mixture was quenched with water
and extracted with diethyl ether. The combined organic
extracts were washed with water and brine. The organic layer
was filtered and dried over anhydrous sodium sulfate. GC-
MS analysis of 1-decyne (12) was carried out using an FFS
ULBON HR-17 capillary column (0.25 mm × 50 m, 60-150
°C, 20 °C/min). The abundances at m/z of 109 and 110 were
analyzed. The percentage of deuterium isotopic composition
of 1-decyne-1-d was found to be 98%.
1
1635, 1265 cm-1; H NMR (CDCl3) δ 8.14 (br d, J ) 7.3 Hz,
2H), 7.61 (br t, J ) 7.3 Hz, 1H), 7.48 (br t, J ) 7.3 Hz, 2H),
2.51 (t, J ) 7.0 Hz, 2H), 1.80-1.20 (m, 12H), 0.89 (t, J ) 6.8
Hz, 3H); MS m/z (relative intensity) 242 (3, M+), 200 (26), 157
(30), 105 (100), 77 (40); HRMS calcd for C17H22O (M+) 242.1671,
found 242.1707.
GC-MS An a lysis of Byp r od u ct Ben zen e in th e Rea c-
tion of Ald eh yd e 2a w ith Dip h en yliod on iu m Sa lt 1a in
DMF -d 7. To a stirred solution of anhydrous CrCl2 (48 mg, 0.39
mmol) doped with NiCl2 (0.5 mol %) in dry DMF-d7 (99.5% D,
0.5 mL) was added a solution of diphenyliodonium tetrafluo-
roborate (1a ) (36 mg, 0.098 mmol) and aldehyde 2a (10 mg,
0.098 mmol) in DMF- -d7 (0.5 mL) under argon at room
temperature, and the solution was stirred for 5 h. The reaction
mixture was quenched with water and extracted with diethyl
ether. The combined organic extracts were washed with water
and brine. The organic layer was filtered and dried over
anhydrous sodium sulfate. GC-MS analysis of byproduct
benzene was carried out using an FFS ULBON HR-1 capillary
column (0.25 mm × 50 m, 50 °C). The abundances at m/z of
78 and 79 were analyzed. The percentage of deuterium isotopic
composition of benzene-d1 was found to be 20%.
Ack n ow led gm en t. This work was supported by a
Grant-in-Aid for Scientific Research on Priority Areas
(A) “The Chemistry of Inter-element Linkage” (No.
09239102) from the Ministry of Education, Science,
Sports, and Culture, J apan.
Ch r om iu m -Med ia ted Rea ction of Ald eh yd e 2a w ith (o-
J O990809Y