Oxidizing ability of a series of (Tropon-2-ylimino)pnictoranes (Pnictogen = P, As, Sb, and Bi) toward some alcohols

Article abstract of DOI:10.1246/bcsj.76.1029

In order to gain a better understanding of the oxidizing ability of a series of (tropon-2-ylimino)pnictoranes of the general structure Ph₃M=NR (R = tropon-2-yl; M = P, As, Sb, and Bi), reactions were run with some alcohols such as benzopinacol (1,1,2,2-tetraphenyl-1,2-ethanediol), benzoin, cinnamyl alcohol, 1-phenylethanol, a mixture of cis- and trans-4-t-butylcyclohexanol, 2-phenylethanol, and 1-phenyl-1,3-propandiol. Iminophosphorane oxidized only benzopinacol to give benzophenone, while both arsorane and stiborane oxidized benzopinacol and benzoin to give benzophenone and benzil, respectively. On the other hand, iminobismuthorane has appreciable oxidizing ability, and reacted with the alcohols mentioned above, except the primary alcohol, to give the corresponding carbonyl compounds. Iminobismuthorane reacted with 1-phenyl-1,3-propandiol selectively to oxidize benzyl alcohol moiety, but not a primary alcohol moiety, to give 3-hydroxy-1-phenyl-1-propanone. Thus, the oxidizing ability of a series of (tropon-2-ylimino)pnictoranes is demonstrated to be in the order of iminophosphorane < iminoarsorane < iminostiborane < iminobismuthorane: the dipolar (degree of contribution of the Ph₃M⁺-^-NR canonical structure) and electrophilic character of pnictogen elements of a series of iminopnictoranes appear to increase their oxidizing ability when the pnictogen stands lower in the periodic table.

Full text of DOI:10.1246/bcsj.76.1029

ꢀ
2003 The Chemical Society of Japan
Bull. Chem. Soc. Jpn., 76, 1029–1034 (2003) 1029
Oxidizing Ability of a Series of (Tropon-2-ylimino)pnictoranes
(
Pnictogen = P, As, Sb, and Bi) toward Some Alcohols
ꢀ
Yuhki Mitsumoto and Makoto Nitta
Department of Chemistry, School of Science and Engineering, Waseda University, Shinjuku-ku, Tokyo 169-8555
(
Received October 30, 2002)
In order to gain a better understanding of the oxidizing ability of a series of (tropon-2-ylimino)pnictoranes of the
general structure Ph3M=NR (R = tropon-2-yl; M = P, As, Sb, and Bi), reactions were run with some alcohols such as
benzopinacol (1,1,2,2-tetraphenyl-1,2-ethanediol), benzoin, cinnamyl alcohol, 1-phenylethanol, a mixture of cis- and
trans-4-t-butylcyclohexanol, 2-phenylethanol, and 1-phenyl-1,3-propandiol. Iminophosphorane oxidized only benzopi-
nacol to give benzophenone, while both arsorane and stiborane oxidized benzopinacol and benzoin to give benzophe-
none and benzil, respectively. On the other hand, iminobismuthorane has appreciable oxidizing ability, and reacted with
the alcohols mentioned above, except the primary alcohol, to give the corresponding carbonyl compounds. Iminobis-
muthorane reacted with 1-phenyl-1,3-propandiol selectively to oxidize benzyl alcohol moiety, but not a primary alcohol
moiety, to give 3-hydroxy-1-phenyl-1-propanone. Thus, the oxidizing ability of a series of (tropon-2-ylimino)pnictor-
anes is demonstrated to be in the order of iminophosphorane < iminoarsorane < iminostiborane < iminobismuthorane:
þ
ꢁ
the dipolar (degree of contribution of the Ph3M – NR canonical structure) and electrophilic character of pnictogen ele-
ments of a series of iminopnictoranes appear to increase their oxidizing ability when the pnictogen stands lower in the
periodic table.
Iminopnictoranes (1a–d) (Ph3M = NR; M = P, As, Sb, Bi)
the synthesis of azaheterocycles has been demonstrated con-
{10
6
are a class of compounds having a formal double bond be-
tween the nitrogen and the pnictogen elements (Fig. 1). In
contrast to extensive works on lighter pnictoranes, the chemis-
try of iminostiborane and iminobismuthorane has been studied
less. The latter compounds have been receiving considerable
attention in view of their chemical analogy to pnictogen ylides
vincingly.
(Vinylimino)phosphoranes undergo a single-
step annulation with compounds containing two electrophilic
centers such as ꢀ-bromo ketones, ꢀ,ꢁ-unsaturated ketones
and aldehydes, as well as the related Michael acceptors to give
8
a variety of nitrogen heterocycles. In relation to these studies,
we have recently been interested in exploiting the synthesis,
structure, and reactivities afforded by (tropon-2-ylimino)phos-
1
{5
as well as their potential utility in organic synthesis.
The
1
1
dipolar and nucleophilic character of the iminopnictoranes ap-
pear to increase, and their stability decrease when the pnicto-
gen stands lower in the periodic table. The difference between
iminophosphoranes and other iminopnictoranes is commonly
ascribed to less efficient pp–dp overlap between the N-p orbi-
tals and the larger and more diffuse 4d, 5d, and 6d orbitals of
arsenic, antimony, and bismuth elements, and decreased elec-
phorane (3a), as well as a series of (tropon-2-ylimino)pnic-
1
2;13
toranes (3b–d) (M = As, Sb, Bi).
The X-ray crystallo-
graphic analysis of 3a,b has revealed that the P–O and As–O
distances are significantly shorter than the sum of the van
der Waals radii of both elements, respectively, and the pnicto-
gens (P and As) and the oxygen atom in 3a,b are held together
1
1;13
by coordination (Fig. 1).
Although compounds 3c,d are
2
;3
trostatic interaction across the imide bonds.
(
The utility of
vinylimino)phosphoranes (2) as useful building blocks for
not isolated in pure form and are prepared in situ due to their
moisture sensitivity, the reaction of 3a–d with heterocumu-
lenes provides a new methodology for constructing new cyclo-
1
1{13
hepta-annulated five-membered heterocycles.
Further-
more, the reactivity of 3a–d has been clarified to be in the
1
1;13
order of 3a < 3b < 3c < 3d. Through these studies, co-
ordination of the oxygen atom to Sb and Bi elements in 3c,d is
also suggested. Iminoarsorane (M = As) appears to be more
resistant to hydrolysis than the iminostiborane (M = Sb) and
1
3
2
;3;13;14
iminobismuthorane (M = Bi),
and can be handled in
air, although it is more labile than its phosphorane analogue.
Since the first preparation of several iminobismuthoranes ac-
1
5
cording to Wittig’s procedure, other improved procedures
have been developed to examine their chemistry in some
1
5;16
15{19
detail. Iminopnictranes (M = Sb,
Bi
) thus far ob-
tained as stable compounds have electron-withdrawing groups
1
5;18
20
Fig. 1.
such as tosyl,
trifluoroacetyl, and trichloroacetyl groups

1
030 Bull. Chem. Soc. Jpn., 76, No. 5 (2003)
Oxidizing Ability of Iminopnictoranes
on the nitrogen atom. Triaryl(tosylimino)bismuthorane reacts
with aromatic aldehyde, benzoyl chloride, and phenyl isocya-
nate to give N-arylmethylene-p-toluenesulfonamide, N-benzo-
preliminary study of a mild oxidation reaction of 3d toward
benzopinacol and cinnamyl alcohol to give benzophenone
1
2
and cinnamaldehyde, we now examine the reactions of 3a–
d with selected alcohols to gain insight into their oxidizing
ability. The reaction conditions and the yields of the products
are summarized in Table 1. Treatment of 3a–d with some al-
cohols led to interesting results: the reaction of 3a with benzo-
pinacol (4) in refluxing xylene gave 2-aminotropone (6), ben-
zophenone (7), and triphenylphosphine (8a), in addition to the
recovery of 3a (Scheme 1, Table 1, Run 1). In this reaction,
8a was obtained in 17% yield, while 7 was obtained in 71%
yield. Thus, ca. 54% of 7 would arise from the thermal re-
action of 4 without intervention of 3a. Actually, the thermal
reaction of 4 in refluxing xylene afforded 7 in 41% yield
(Table 1, Run 2). On the other hand, the reaction of 4 in
the presence of triphenylphosphine oxide (9a) afforded 7 and
recovery of 4 in yields similar to those of the thermal reaction
(Table 1, Run 3). The compound 9a was recovered without
formation of triphenylphosphine (8a), and thus, 9a does not
0
yl-p-toluenesulfonamide, and N-aryl-N -tosylurea, respecti-
1
7
vely. Recently, triaryl(3,5-ditrifluoromethylbenzoylimino)-
bismuthorane has been shown to oxidize even primary
2
1
22
alcohols, as in the case of triarylbismuthine oxide and other
pentavalent organobismuth reagents,4 which act as efficient
oxidizing agents toward a wide range of alcohols. Although
triaryl(tosylimino)bismuthorane and triaryl(trifluoroacetylimi-
no)bismuthorane have been shown to exhibit oxidizing proper-
;23
ties toward some activated alcohols, converting them into the
triaryl(tosylimino)sti-
corresponding carbonyl compounds,1
6;20
borane oxidizes benzopinacol and benzoin to give benzophen-
1
6
one and benzil. Thus, the oxidizing ability of iminopnictor-
anes seems to be dependent not only on the pnictogen element
but also on the substituent involved in pnictoranes. Since the
oxidizing ability of a series of iminopnictoranes (pnictogen =
P, As, Sb, Bi) has not been demonstrated so far, we investi-
gated the reaction of 3a–d (pnictogen = P, As, Sb, Bi) with
selected alcohols to give the corresponding carbonyl
compounds. We report herein the results in detail.
2
2
act as an oxidizing agent.
Similarly, the reaction of 3b–d
with 4 in refluxing toluene, in PhH at rt, and in CH2Cl2 at
rt, respectively, afforded 6, 7, and triphenylpnictine (8b–d)
in good yields (Scheme 1, Table 1, Runs 4, 7, and 8). The
thermal reaction of 4 in the absence or presence of triphenylar-
sine oxide 9b afforded a small amount of 7, which derives
from the thermal process, in addition to recovery of 4 (Runs
5 and 6). Thus, triphenylarsine oxide 9b also does not seem
Results and Discussion
The preparation of iminophosphorane (3a)11 and in situ pre-
paration of iminoarsorane 3b, iminostiborane (3c), and imino-
bismuthorane (3d) were accomplished according to the proce-
dures described previously.1
2;13
Since we have reported a
to have oxidizing ability toward 4, as in the case of 9a.
22
Table 1. Results for the Reaction of Iminopnictoranes (3a–d) with Some Alcohols
a)
b)
Pnictorane
Reaction conditions
Product (Yield/%)
Run
3a–d
Alcohol
Solvent
Temp
Time/h
Carbonyl compd
Remaining compd
1
2
3
4
5
6
7
8
9
3a
4
4
4
4
4
4
4
4
11
11
11
11
11
11
14
14
14
16
16
18
18
20
22
Xylene
Xylene
Xylene
Toluene
Toluene
Toluene
PhH
CH2Cl2
Xylene
Xylene
Toluene
Toluene
PhH
reflux
reflux
reflux
reflux
reflux
reflux
rt
1
1
1
1.5
1.5
1.5
2
7 (71)
7 (41)
7 (30)
7 (88)
7 (5)
3a (9), 6 (37), 8a (17)
4 (50)
4 (58), 9a (99)
6 (87), 8b (92)
4 (94)
4 (83), 9b (86)
6 (97), 8c (92)
6 (90), 8d (92)
3a (79), 11 (0), 8a (0)
11 (0)
None
9a
3b
None
9b
3c
3d
3a
None
3b
None
3c
3d
3b
3c
3d
3c
3d
3c
7 (16)
7 (92)
7 (95)
12 (57)
12 (91)
12 (97)
12 (42)
12 (95)
12 (6)
15 (0)
15 (0)
15 (85)
17 (0)
17 (53)
19 (0)
19 (57)
21 (0)
23 (84)
rt
1
reflux
reflux
reflux
reflux
reflux
rt
reflux
reflux
rt
reflux
rt
reflux
rt
43
43
25
25
1.5
43
19
19
5
15
5
24
18
46
3
10
11
12
13
14
15
16
17
18
19
20
21
22
23
6 (97), 8b (97)
11 (40)
6 (100), 8c (96)
6 (100), 11 (75), 8d (59)
6 (73), 14 (73), 9b (66)
6 (90), 14 (94)
6 (96), 8d (65)
6 (100), 16 (94)
6 (93), 8d (57)
6 (87), 18 (100)
6 (93), 8d (59)
6 (60), 20 (61), 8d (70)
6 (95), 8d (42)
c)
d)
d)
d)
CH2Cl2
Toluene
PhH
CH2Cl2
PhH
CH2Cl2
PhH
3d
3d
3d
CH2Cl2
CH2Cl2
CH2Cl2
rt
rt
a) Identified on the basis of comparison of physical data with those of the authentic specimens. b) Isolated yield
through column chromatography and/or TLC. c) Reaction carried out under reflux did not improve the yields. d) For-
mation of Ph3SbO is expected through hydrolysis of unreacted 3c and/or pentavalent intermediates under workup con-
ditions (column chromatography and/or TLC), but it is known to exist as polymer and not isolated here (Ref. 24).

Y. Mitsumoto et al.
Bull. Chem. Soc. Jpn., 76, No. 5 (2003) 1031
Scheme 2.
to the recovery of 3a (Scheme 2, Table 1, Run 9). The forma-
tion of 12 is similar to the thermal reaction of 11 (Run 10).
Thus, 3a does not act as oxidizing agent toward 11. Unlike
in the case of 3a, iminoarsorane (3b) oxidizes 11 to give 6,
1
2, and 8b in quantitative yields, respectively (Run 11).
Although the thermal reaction of 11 also gives 12 in modest
yield (Run 12), the quantitative yield of 8b (Run 11) suggests
that the oxidation reaction of 3b occurs smoothly as compared
with the pure thermal process. Similarly, the oxidation reac-
tions of 3c and 3d with 11 in refluxing PhH and in refluxing
CH2Cl2, respectively, to yield 6, 12, and triphenylpnictanes
(8c,d), suggests the appreciable oxidizing ability of 3c and
3d (Runs 13 and 14). Details are ambiguous at this stage,
however, repeated reactions of 11 and 3d did not cause com-
plete consumption of 11 (Run 14). Regarding the hydrolysis
Scheme 1.
Plausible reaction pathways for these oxidations are de-
picted in Scheme 1. Iminopnictoranes (3a–d) with 4 react to
form cyclic pentavalent intermediates (5a–d),1
undergo ligand cleavage to give 7. Regarding the reactivities
of 3a–d toward 4, the formation of 5b–d and their concomitant
elimination of 6, and subsequent reaction to give 7 and 8b–d
seems to proceed smoothly, while 3a would form 5a ineffi-
ciently, and an appreciable amount of the thermal decomposi-
tion of 4 occurs to give 7 (Runs 1 and 2 vs Runs 4 and 5). The
structures and properties of a series of (acylimino)pnictoranes
6;20;21;23
which
1
3
21
of 3a–d and the nature of the M=N bond (vide supra),
11 and 3a–d would react to give 13a–d, which probably exist
in an equilibrium with 3a–d and 11. The intermediates 13b–d
then eliminate the tropon-2-ylamino group and the ꢀ-hydrogen
of the alkoxy function simultaneously to form 6, 12, and 8b–
(
Ar3M=NCO– and H3M=NCOCF3; M = P, As, Sb, Bi) are
1
6
compared based on spectroscopy, X-ray analysis, and ab initio
molecular orbital calculations. It was found that the contri-
d. In the reaction of 3a with 11, the formation of 13a and
its reductive elimination of the (tropon-2-yl)amino group, 12,
and 8a would become less efficient.
21
þ
ꢁ
bution of the M –N=C–O canonical structure becomes more
prominent and the single bond character of the M=N bond in-
creases progressively as the pnictogen atom becomes heavier,
probably due to the difference in orbital size and electronega-
tivity between the pnictogen and nitrogen atoms. These fea-
tures are expected for compounds 3a–d based on the reactivity
toward heterocumulenes.13 Thus, the formation 5a–d occurs
more easily in the order of 3a < 3b < 3c < 3d, and their re-
ductive elimination of 7 would also be efficient in that order.
Consequently, regarding the reaction time and the reaction
temperature concerning 3a–d (Runs 1, 4, 7, and 8), the oxidiz-
ing ability is clearly suggested to be in the order of 3a < 3b <
In order to evaluate further the oxidizing properties of 3b–d,
they were treated with an allylic alcohol and a cinnamyl alco-
hol (14) in refluxing toluene, in refluxing benzene, and in
CH2Cl2 at rt, respectively, (Scheme 3). The former two pnic-
toranes do not exhibit oxidizing ability and compound 6,
which arises from the hydrolysis of 3b,c under workup condi-
tions, along with most of the starting material 14 were recov-
ered (Runs 15 and 16). In contrast, compound 3d exhibited re-
markable oxidizing ability to give 6, aldehyde (15), and 8d in
good yields (Run 17). Similarly, 3c did not oxidize secondary
alcohols, 1-phenylethanol (16) and a mixture of cis- and trans-
4-t-butylcyclohexanol (18) (Runs 18 and 20), but 3d oxidized
16 and 18 to give acetophenone (17) and cyclohexanone (19),
along with 6 and 8d (Runs 19 and 21). However, compound
3d did not oxidize primary alcohol (20) even under prolonged
reaction time, and 20 was recovered (Run 22). In this case,
compound 6 and 8d were also obtained, suggesting the thermal
decomposition of 3d occurs in the protic media of 20.1 So we
3
c < 3d. Triphenylstibine and triphenylbismuthine oxides are
known to exist as dimeric and polymeric substances, and they
are known to oxidize both benzopinacol (4) and benzoin (11)
to give 7 and benzil (12), however, compounds 9a,b are clar-
ified to be inert toward 4.2
2;24
On the other hand, the reaction of 3a with 11 in refluxing
xylene did not give 8a, and benzil (12) is obtained in addition
3

1
032 Bull. Chem. Soc. Jpn., 76, No. 5 (2003)
Oxidizing Ability of Iminopnictoranes
sidered to depend on the oxidizing ability of the pnictogen ele-
ments and the reactivity of the ꢀ-hydrogen of the incorporated
alkoxy moiety. Since selective oxidation of compound 22 oc-
curs to give 23, the pentavalent intermediate (24d) would exist
in equilibrium between the intermediates (25) and (26), and the
more active ꢀ-hydrogen is eliminated via 26. Although details
are ambiguous at this stage, an alternative pathway for the se-
lective oxidation of 22 would be a formation of 27, which
eliminates the more active ꢀ-hydrogen. In addition, only the
oxidation reaction of 4 with 3d resulted in the formation of
8
d in good yield (Run 8), while reactions with other alcohols
resulted in the modest yields of 8d (Runs 14, 17, 19, 21 and
3). A plausible explanation would be the following: during
2
the reductive elimination of alcohols, 2-aminotropone (6),
and triphenylbismuthine (8d) from the pentavalent intermedi-
ates (13) (M = Bi) and (24d) (M = Bi), the ꢀ-hydrogen is ab-
stracted alternatively by the phenyl group on the bismuth ele-
ment to result in the formation of benzene and a bismuth
2
1;23
compound, which are not isolated at the present stage.
In conclusion, we have demonstrated the oxidizing ability of
a series of (tropon-2-ylimino)pnictoranes (3a–d). It is clarified
for the first time that the iminophosphorane (3a) oxidizes only
benzopinacol (4), while iminoarsorane (3b) and iminostibor-
ane (3c) oxidize benzopinacol (4) and benzoin (11). Com-
pounds (3b,c) do not oxidize allylic and benzylic alcohols
(
14) and (16). On the other hand, iminobismuthorane (3d) oxi-
dizes allylic alcohol (14), benzylic alcohol (16), and even
trans-4-t-butylcyclohexanol (18). Compound (3d) is inert to-
ward primary alcohol, 2-phenylethanol (20), and selective oxi-
dation of 1-phenyl-1,3-propanediol (22) occurrs to give 23.
Through the present investigations, the oxidizing ability of a
series of iminopnictoranes (3a–d) toward alcohols is demon-
strated to be in the order of 3a < 3b < 3c < 3d: the dipolar
þ ꢁ
(
degree of contribution of the Ph3M – NR canonical struc-
ture) and electrophilic character of pnictogen elements of a
series of iminopnictoranes appear to increase their oxidizing
ability when the pnictogen stands lower in the periodic table.
Experimental
Compounds Ph3AsBr2,25 Ph3SbCl2,26 and Ph3-
General.
2
7
BiCl2 were prepared according to the procedures reported in
the literature. (Tropon-2-ylimino)phosphorane (3a) was prepared
by the method reported in the previous paper.11 In situ generation
of iminoarsorane (3b), iminostiborane (3c), and iminobismuthor-
ane (3d) was performed according to the previous paper.13 All
the reactions were carried out under anhydrous conditions and
dry nitrogen atmosphere.
Scheme 3.
Reaction of (Tropon-2-ylimino)phosphorane (3a) with Ben-
zopinacol (4) and Benzoin (11). A solution of 3a (95 mg, 0.25
mmol) and an alcohol [4 (92 mg, 0.25 mmol); 11 (53 mg, 0.25
next investigated the selectivity for dihydroxy compound (22),
which is composed of benzylic and primary hydroxy groups
3
mmol)], in dry xylene (5 cm ) was heated under reflux for the per-
(Run 23). In this case, the IR spectrum of the product 23 ex-
iod indicated in Table 1. After evaporation of the solvent, the re-
sidue was separated by TLC on SiO2 (hexane:AcOEt/5:1) to give
the products (Table 1, Runs 1 and 9).
hibited one carbonyl absorption due to a ketone but not an al-
dehyde, and the structure was confirmed on the basis of com-
parison of the spectral data with those of the authentic
specimen. The reactions of 3b–d with alcohols (14), (16),
Thermal Reaction of Benzopinacol (4) in the Absence or
Presence of Ph3PO. A solution of 4 (95 mg, 0.25 mmol) in xy-
3
(
18), (20), and (22) would proceed also via a common penta-
lene (5 cm ) in the absence or presence of Ph PO (70 mg, 0.25
3
valent intermediate (24b–d) (vide supra). In these reactions,
the concomitant elimination of the tropon-2-ylamino group,
the oxidized carbonyl compounds, and 8b–d from 24 is con-
mmol) was heated under reflux for 1 h. After evaporation of
the solvent, the residue was separated by TLC on SiO (hexane:
AcOEt/5:1) to give the products (Table 1, Runs 2 and 3).
2

Y. Mitsumoto et al.
Bull. Chem. Soc. Jpn., 76, No. 5 (2003) 1033
t
Thermal Reaction of Benzoin (11). A solution of 11 (53 mg,
3
Bu OK (112 mg, 1 mmol), and then stirred for 5 min at rt. To this
mixture was added an alcohol [20 (62 mg, 0.5 mmol) or 22 (78
mg, 0.5 mmol)], and then stirred at rt for the period indicated in
Table 1. After evaporation of the solvent, the residue was chro-
matographed on SiO2. The fractions eluted with CH2Cl2 afforded
a mixture of 8d and alcohol 20, and the mixture was further sepa-
rated by TLC on SiO2 (hexane:AcOEt/5:1) to give 8d and 20 or
8d and 23. The fractions eluted with AcOEt afforded 6 (Table
1, Runs 22 and 23).
0
.25 mmol) in xylene (5 cm ) was heated under reflux for 43 h.
After evaporation of the solvent, the residue was purified by
TLC on SiO2 (hexane:AcOEt/5:1) to give the products (Table 1,
Run 10).
Reaction of (Tropon-2-ylimino)arsorane (3b) with Benzopi-
nacol (4), Benzoin (11), and Cinnamyl Alcohol (14). To a stir-
red solution of Ph3AsBr2 (117 mg, 0.25 mmol) and 6 (30 mg, 0.25
3
mmol) in toluene (6 cm ) was added NEt3 (51 mg, 0.50 mmol) in
3
toluene (1 cm ), and then stirred for 2 h at rt. To this mixture was
added an alcohol [4 (92 mg, 0.25 mmol), 11 (53 mg, 0.25 mmol),
Financial support from Waseda University Grants for Spe-
cial Research Projects is gratefully acknowledged.
1
4 (33 mg, 0.25 mmol)], and then this mixture was heated under
reflux for the period indicated in Table 1. After evaporation of the
solvent, the residue was separated by TLC on SiO2 (hexane:
AcOEt/5:1) to give the products (Table 1, Runs 4, 11, and 15).
Thermal Reaction of Benzopinacol (4) in the Absence or
Presence of Ph3AsO. A solution of 4 (95 mg, 0.25 mmol) in tol-
References
1
A. W. Johnson, ‘‘Ylides and Imines of Phosphorus,’’ John
Wiley & Sons, New York, Chichester, Brisbane, Toronto, Singa-
pore (1993).
3
uene (5 cm ) in the absence or presence of Ph3AsO (81 mg, 0.25
mmol), was heated under reflux for 1.5 h. After evaporation of the
solvent, the residue was separated by TLC on SiO2 (hexane:
AcOEt/5:1) to give the products (Table 1, Runs 5 and 6).
Reaction of (Tropon-2-ylimino)stiborane (3c) with Benzopi-
nacol (4) and Benzoin (11). To a stirred solution of Ph3SbCl2
2
16, 45 (1987).
D. Lloyd, I. Gosney, and R. A. Ormiston, Chem. Soc. Rev.,
3
D. Lloyd and I. Gosney, in ‘‘The Chemistry of Organic Ar-
senic, Antimony and Bismuth Compound,’’ ed by S. Patai, John
Wiley & Sons, Chichester, New York, Brisbane, Toronto, Singa-
pore (1994), pp. 657–693.
(
106 mg, 0.25 mmol) and 6 (30 mg, 0.25 mmol) in dry PhH (3
3
t
cm ) was added Bu OK (56 mg, 0.5 mmol) and then stirred for
0 min at rt. To this reaction mixture was added an alcohol [4
92 mg, 0.25 mmol); 11 (53 mg, 0.25 mmol)], and stirred at rt
4
N. C. Norman, ‘‘Chemistry of Arsenic, Antimony and Bis-
3
(
muth,’’ Blackie Academic Professional, London, Weinheim, New
York, Tokyo, Melbourne, and Madras (1998).
or heated under reflux for the period indicated in Table 1. After
evaporation of the solvent, the residue was separated by column
chromatography on SiO2. Fractions eluted with CH2Cl2 gave a
mixture of 8c and oxidized product. Fractions eluted with AcOEt
afforded 6. The former mixture was further separated by TLC on
SiO2 (hexane:AcOEt/5:1) to give 8c and oxidized product
5
H. Suzuki and Y. Matano, ‘‘Organobismuth Chemistry,’’
Elsevier, Amsterdam, London, New York, Oxford, Paris, Shan-
non, Tokyo (2001).
6
a) Yu. G. Gololobov, I. N. Zhmurova, and L. F. Kasukhin,
Tetrahedron, 37, 437 (1981). b) Yu. G. Gololobov and L. F.
Kasukhin, Tetrahedron, 48, 1353 (1992).
(
Table 1, Runs 7 and 13).
Reaction of (Tropon-2-ylimino)stiborane (3c) with Alcohols
7
S. Eguchi, Y. Matsushita, and K. Yamashita, Org. Prep.
Proced. Int., 24, 209 (1992).
M. Nitta, Rev. Heteroat. Chem., 9, 87 (1993), and refer-
ences cited therein.
(
mmol) and 6 (30 mg, 0.25 mmol) in dry PhH (5 cm ) was added
Bu OK (56 mg, 0.5 mmol) and then stirred for 30 min at rt. To
14) and (16). To a stirred solution of Ph3SbCl2 (106 mg, 0.25
8
3
t
9
P. Molina and M. J. Vilaplana, Synthesis, 1994, 1197.
this reaction mixture was added an alcohol [14 (33 mg, 0.25
mmol); 16 (31 mg, 0.25 mmol)], and heated under reflux for the
period indicated in Table 1. After evaporation of the solvent,
the residue was separated by column chromatography on SiO2.
The fractions eluted with AcOEt gave 6 and unreacted 14 and
10 H. Wamhoff, G. Richardt, and M. St o¨ lben, Adv. Hetero-
cycl. Chem., 64, 159 (1995).
11 H. Yamamoto, M. Ohnuma, and M. Nitta, J. Chem. Res.,
Synop., 1999, 173; J. Chem. Res., Miniprint, 1999, 901.
12 M. Nitta and Y. Mitsumoto, Heterocycles, 55, 629 (2001).
13 M. Nitta, Y. Mitsumoto, and H. Yamamoto, J. Chem. Soc.,
Perkin Trans. 1, 2001, 1901.
1
6 (Table 1, Runs 16 and 18).
Reaction of (Tropon-2-ylimino)bismuthorane (3d) with
Benzopinacol (4), Benzoin (11), and Alcohols (14), (16), and
18). To a solution of Ph3BiCl2 (128 mg, 0.25 mmol) and 2-ami-
14 R. Appel and D. Wagner, Angew. Chem., 72, 209 (1960).
15 G. Wittig and D. Hellwinkel, Chem. Ber., 97, 789 (1964).
16 H. Suzuki and T. Ikegami, J. Chem. Res., Synop., 1996, 24.
17 H. Suzuki, C. Nakaya, Y. Matano, and T. Ogawa, Chem.
Lett., 1991, 105.
(
3
notropone 6 (30 mg, 0.25 mmol) in CH2Cl2 (3 cm ) was added
t
Bu OK (56 mg, 0.5 mmol), and then stirred for 5 min at rt. To
this mixture was added an alcohol [4 (92 mg, 0.25 mmol); 11
(
53 mg, 0.25 mmol); 14 (33 mg, 0.25 mmol); 16 (31 mg, 0.25
18 S. V. Pasenok, N. V. Kirij, Y. L. Yagupolskii, D.
Naumann, and W. Tyrra, J. Fluorine Chem., 63, 179 (1993).
19 T. Ikegami and H. Suzuki, Organometallics, 17, 1013
(1998).
20 Y. Matano, H. Nomura, M. Shiro, and H. Suzuki, Organo-
metallics, 18, 2580 (1999).
21 Y. Matano, H. Nomura, H. Suzuki, M. Shiro, and H.
Nakano, J. Am. Chem. Soc., 123, 10954 (2001).
22 Y. Matano and H. Nomura, J. Am. Chem. Soc., 123, 6443
(2001).
mmol); 18 (39 mg, 0.25 mmol), 20 (31 mg, 0.25 mmol), 22 (38
mg, 0.25 mmol)], and then stirred at rt for the period indicated
in Table 1. After evaporation of the solvent, the residue was chro-
matographed on SiO2. The fractions eluted with CH2Cl2 afforded
a mixture of 8d and oxidized product, and the mixture was further
separated by TLC on SiO2 (hexane:AcOEt/5:1) to give 8d and
oxidized product. The fractions eluted with AcOEt afforded 6
(
Table 1, Runs 8, 14, 17, 19, and 21).
Reaction of (Tropon-2-ylimino)bismuthorane (3d) with Al-
cohols (20) and (22). To a solution of Ph3BiCl2 (256 mg, 0.5
mmol) and 6 (60 mg, 0.5 mmol) in CH2Cl2 (6 cm ) was added
23 a) D. H. R. Barton and J.-P. Finet, Pure Appl. Chem., 59,
937 (1987). b) J.-P. Finet, Chem. Rev., 89, 1487 (1989).
3

1
034 Bull. Chem. Soc. Jpn., 76, No. 5 (2003)
Oxidizing Ability of Iminopnictoranes
2
4
H. Suzuki, T. Ikegami, and Y. Matano, Tetrahedron Lett.,
5, 8197 (1994).
A. D. Beveridge and G. S. Harris, J. Chem. Soc. A, 1964,
26 A. D. Beveridge, G. S. Harris, and F. Inglis, J. Chem. Soc.
A, 1966, 520.
27 G. Wittig and K. Clauss, Liebigs Ann. Chem., 578, 136
3
2
5
6
076.
(1952).