Synthesis, Structure, and Bonding of 1-Oxa-6,6aλ4- chalcogenopentalenes and Related Derivatives; The Role of Intramolecular Coordination

Article abstract of DOI:10.1021/acs.joc.6b00173

The synthesis and characterization of a series of alicyclic organochalcogen compounds derived from 2-chloro-1-formyl-3-hydroxymethylenecyclohexene (16) are described. The reaction of 16 with disodium disulfide afforded an unexpected 1-oxa-6,6aλ⁴-dithiapentalene 33, whereas the reaction of disodium diselenide afforded 1-oxa-6,6aλ⁴-diselenapentalene 34, along with 1,6-dioxa-6a-selenapentalene 35. In contrast, when 16 was treated with Na₂Te₂, it resulted in the formation of 1-oxa-6,6aλ⁴-ditellurapentalene 36 along with 1,6-dioxa-6a-tellurapentalene 37 and cyclic monotelluride 38. The oxidation of 1-oxa-6,6aλ⁴-diselenapentalene 34 with m-CPBA provided the corresponding 1-oxa-6,6aλ⁴-diselenapentalene-6,6aλ⁴-dioxide 39 in which both of the selenium atoms were found to be oxidized. The 1-oxa-6,6aλ⁴-dichalcogenopentalenes 33, 34, and 36 are stabilized by 3c-4e bond resulting from intramolecular E?O interaction. The donor oxygen donates a lone pair of electrons to the σ? orbital of acceptor E-E bond (E = S, Se, and Te) whose σ bond already has its bond pair electrons. The existence of intramolecular E?O interactions was established by multinuclear NMR spectroscopy, single crystal X-ray analysis, and computational studies. The single crystal X-ray structures of compounds 33, 34, and 36 reveal that the molecules are almost planar. Nucleus-independent chemical shifts were calculated to compare the aromaticity in both the five-membered rings of 33, 34, 36 and 1,6-dioxa-6a-chalcopentalenes (35 and 37). The isotropic shift values of the covalently fused five-membered heterocyclic rings are more negative than the five-membered heterocyclic rings formed by intramolecular coordination.

Full text of DOI:10.1021/acs.joc.6b00173

Article
pubs.acs.org/joc
Synthesis, Structure, and Bonding of 1‑Oxa-6,6aλ4-
chalcogenopentalenes and Related Derivatives; The Role of
Intramolecular Coordination
Poonam Rajesh Prasad,† Karuthapandi Selvakumar,† Harkesh B. Singh,*,† and Ray J. Butcher‡
†Department of Chemistry, Indian Institute of Technology Bombay, Powai, Mumbai 400076, India
‡Department of Chemistry, Howard University, Washington, DC 20059, United States
S
* Supporting Information
ABSTRACT: The synthesis and characterization of a series of alicyclic organochalcogen
compounds derived from 2-chloro-1-formyl-3-hydroxymethylenecyclohexene (16) are
described. The reaction of 16 with disodium disulfide afforded an unexpected 1-oxa-
6,6aλ4-dithiapentalene 33, whereas the reaction of disodium diselenide afforded 1-oxa-
6,6aλ4-diselenapentalene 34, along with 1,6-dioxa-6a-selenapentalene 35. In contrast, when
16 was treated with Na2Te2, it resulted in the formation of 1-oxa-6,6aλ4-ditellurapentalene
36 along with 1,6-dioxa-6a-tellurapentalene 37 and cyclic monotelluride 38. The oxidation
of 1-oxa-6,6aλ4-diselenapentalene 34 with m-CPBA provided the corresponding 1-oxa-
6,6aλ4-diselenapentalene-6,6aλ4-dioxide 39 in which both of the selenium atoms were found
to be oxidized. The 1-oxa-6,6aλ4-dichalcogenopentalenes 33, 34, and 36 are stabilized by
3c-4e bond resulting from intramolecular E···O interaction. The donor oxygen donates a
lone pair of electrons to the σ* orbital of acceptor E−E bond (E = S, Se, and Te) whose σ
bond already has its bond pair electrons. The existence of intramolecular E···O interactions
was established by multinuclear NMR spectroscopy, single crystal X-ray analysis, and computational studies. The single crystal X-
ray structures of compounds 33, 34, and 36 reveal that the molecules are almost planar. Nucleus-independent chemical shifts
were calculated to compare the aromaticity in both the five-membered rings of 33, 34, 36 and 1,6-dioxa-6a-chalcopentalenes (35
and 37). The isotropic shift values of the covalently fused five-membered heterocyclic rings are more negative than the five-
membered heterocyclic rings formed by intramolecular coordination.
6b.17−19 Similar observations were also reported by Mugesh
INTRODUCTION
■
and co-workers20 where the attempted synthesis of bis(N,N-
The chemistry of arylchalcogen derivatives having intra-
molecular E···X (E = Se, Te; X = N, O, S) secondary bonding
interaction (SBI) has attracted considerable current interest
owing to their use in various fields such as (a) stabilization and
dimethyl 2,6-oxazoline)-2-phenyl diselenide resulted in the
isolation of ebselen analogue 7 via intramolecular cyclization.
However, the analogous diselenides with one coordinating
isolation of unstable organochalcogen compounds,1−5 (b) as
group at ortho position are quite stable. Attempts to synthesize
reagents in organic synthesis,6−10 (c) precursors for nanoma-
4-tert-butyl-2,6-di(formyl)phenylselenenyl bromide from the
reaction of bis(2,6-diformyl-4-tert-butylphenyl)diselenide21
terials,11,12 and (d) selenoenzyme mimics.5,13−15 In addition to
with bromine resulted in the formation of novel cyclic
these, the intramolecular interactions are also responsible for
selenenate ester 8. Similarly Selvakumar et al.22 and Singh et
al.23 demonstrated the isolation of novel selenenate esters 9a−
9b and 10a−10c, respectively. Parnham et al.24 isolated the
ebselen analogues 11 owing to the presence of two
coordinating groups. Back and co-workers and Singh and co-
workers have isolated the bicyclic selenuranes 1225 and 13a,26
respectively, via oxidation reaction of selenides containing two
hydroxyl or carboxyl groups, while bicyclic tellurane 13b was
isolated from the oxidation reaction of telluride having two
ester groups.27 Recently, Selvakumar et al. isolated the
tellurenate ester 14,27 which was stabilized by strong intra-
molecular coordination.
the specific redox activity of organochalcogen compounds.16
Recently, much attention has been devoted to the arylchalc-
ogen derivatives having two ortho coordinating groups because
of their contrasting reactivity and stability compared to the
analogous compounds with one ortho coordinating group. For
example, the attempted synthesis of respective oxides of 2,6-
bis[(dimethylamino)methyl]phenyl methyl selenide and tel-
luride, having two intramolecularly coordinating amino groups,
resulted in the isolation of novel selenenium 1 and tellurenium
2 cations, respectively (Chart 1).1 Kersting et al. and Zade et al.
reported that the attempted synthesis of N,N-dialkyl/diphenyl-
isophthalamides and N,N-dialkyl/diphenyl-2-bromo-5-tert-bu-
tylisophthalamides dichalcogenides having two amide groups
always led to the formation of cyclized ebselen derivatives 3a−
4b and the corresponding sulfur and tellurium analogues 5a−
Received: January 26, 2016
© XXXX American Chemical Society
A
DOI: 10.1021/acs.joc.6b00173
J. Org. Chem. XXXX, XXX, XXX−XXX

The Journal of Organic Chemistry
Article
Chart 1. 2,6-Disubstituted Aryl-Based Selenium Derivatives
The theoretical studies on facile cyclization of diaryl
diselenides/aryl selenenyl halides revealed that both the
presence of additional coordinating group (steric crowding)
and strong intramolecular interaction introduce a distortion in
the planarity of the aromatic ring which leads to facile
intramolecular cyclization and in no case the desired diselenide
could be isolated.22
In view of the novel reactivity of the diaryl dichalcogenide/
aryl chalcogenyl halides and related derivatives having two
groups R and R′ (where R and R′ = CHO, COOH, COOMe,
COONHR, CH2OH, and NO2) derived from aryl bromide
(e.g., 15, Chart 2), with Na2E2 (E = Se, Te), we decided to
Interestingly, the reactions of 2-chloro-1-formyl-3-hydrox-
ymethylenecyclohexene (16) with disodium dichalcogenides
afforded new classes of unexpected 1-oxa-6,6aλ4-dichalcogeno-
pentalenes and 1,6-dioxa-6a-chalcogenopentalenes, where three
chalcogen atoms were bonded in a linear fashion (vide infra).
Such types of unsymmetrical 1-oxa-6,6aλ4-dichalcogenopenta-
lenes stabilized by intramolecular interaction are not well
studied. Only a few examples are reported with sulfur.29,30 For
instance, 1,6-dioxa-6a-chalcogenopentalenes have been pre-
pared by using different synthetic strategies (Chart 3). 1,6,6aλ4-
Trithiapentalene (17)31 was one of the first examples having
two fused thiapentalene rings. This has been studied extensively
for the planarity of the fused five-membered heterocyclic rings
and unique C2v-symmetric structure at the tricoordinate central
sulfur atom.32−34 Subsequently, related structures and their aza
analogues were reported (18−29).35−41 1,6-Dioxa-6aλ4-thia42
(25−26) and selenapentalene39 (27−28) were prepared by the
reaction of pyran-4-thiones and pyran-4-selones, respectively, in
the presence of thallium trifluorate. Later, Detty et al.43
reported the synthesis of the first tellurium analogue, 2,5-
diphenyl-1,6-dioxa-6aλ4-tellurapentalene (29) by the reaction
of 3-methyl-5-phenyl-l,2-oxatellurol-ium chloride with benzyl
chloride. This class of compounds is interesting in terms of
their structure and bonding and is used as sensitizers in
electrographic compositions. These are also used as molecular
electron donors and charge emitters in multilayer photo-
conductive elements.44
Chart 2. Disubstituted Aryl and Alicyclic-Based Precursors
explore the reactivity of the analogous alicyclic precursor with
Na2E2 (E = S, Se, Te). The precursor 2-chloro-1-formyl-3-
hydroxymethylenecyclohexene (16) exists in two resonance
structures, i.e., enol form (16) and keto form (16′). The enol
form is expected to be more predominant in solution state
rather than the keto form due to the resonance stabilization in
the former. These types of skeletons are commonly used in the
synthesis of organic dyes and polymer chemistry.28
Herein, we describe a new methodology for the synthesis of
intramolecularly stabilized 1-oxa-6,6aλ4-dichalcogenopentalenes
Chart 3. 1,6-Dioxa-6aλ4- chalcopentalene Derivatives
B
DOI: 10.1021/acs.joc.6b00173
J. Org. Chem. XXXX, XXX, XXX−XXX

The Journal of Organic Chemistry
Article
a
Scheme 1. Reaction of Na2S2 with 16
a
Reagents and conditions: (i) Na2E2 (E = S, Se, Te), THF, HMPA, reflux, 6 h; (ii) m-CPBA, dry CH2Cl2, −78 °C.
Scheme 2. Plausible Mechanism for the Formation of 1-Oxa-6,6aλ4-dichalcogenopentalenes (33, 34 and 36) and 1,6-Dioxa-6a-
chalcogenopentalenes (35 and 37)
and related derivatives in one-pot synthesis and describe their
structure and bonding.
afforded 1-oxa-6,6aλ4-dithiapentalene 33 (Scheme 1). The
compounds were purified by column chromatography using
petroleum ether and ethyl acetate (2−10%) as eluent.
In the reaction of disodium diselenide, the first fraction
isolated was 1-oxa-6,6aλ4-diselenapentalene 34 as an orange
solid. The second fraction was 1,6-dioxa-6a-selenapentalene 35
as a yellow colored solid, and the third fraction was as a maroon
sticky colored solid (could not be characterized). The fourth
fraction was the unreacted starting material 16. Similarly, in the
case of the Na2Te2 reaction, four fractions were obtained. The
first fraction isolated was 1-oxa-6,6aλ4-ditellurapentalene 36 as a
red colored solid, and the second fraction was 1,6-dioxa-6a-
tellurapentalene 37 as a yellowish orange colored solid. The
third fraction was cyclic monotelluride 38 as a dark red solid,
and fourth one was the unreacted starting material 16. The
yield of the 1-oxa-6,6aλ4-ditellurapentalene 36 is quite low in
comparison to 1-oxa-6,6aλ4-dithaentalene 33 and 1-oxa-6,6aλ4-
diselenapentalene 34.
RESULTS AND DISCUSSION
■
Synthesis. The precursor, 2-chloro-1-formyl-3-hydroxyme-
thylenecyclohexene (16), was prepared by the reaction of
cyclohexanone with phosphorus oxychloride and dimethylfor-
mamide by following the literature procedure45 with slight
modification in the aqueous workup. Compound 16 is not
stable even at low temperature and decomposes rapidly within
2 days at room temperature and must be handled with care.
Therefore, the reactions were carried out with freshly prepared
16 to give good yields of the products. Attempted synthesis of
desired diorganodichalcogenides 30−32 by the reaction of 16
with disodium dichalcogenides (Na2E2; E = S, Se, Te) under
reflux condition led to the formation of unexpected 1-oxa-
6,6aλ4-dichalcogenopentalenes 33, 34, 36 and 1,6-dioxa-6a-
chacogenopentalenes 35 and 37. The reaction of Na2S2 with 16
C
DOI: 10.1021/acs.joc.6b00173
J. Org. Chem. XXXX, XXX, XXX−XXX

The Journal of Organic Chemistry
Article
A quick understanding of the formation of 1-oxa-6,6aλ4-
dichalcogenopentalenes and the 1,6-dioxa-6a-chalcogenopenta-
lenes could be reached by invoking the nature of juxtaposed
chalcogen−chalcogen interactions. In general, when the
divalent central chalcogen encounters more than one peripheral
chalcogens, the nonbonded interaction becomes repulsive.1,46
As a result, the entire system tries to readjust to stabilize itself
via either conformational rearrangement or undergoing further
reaction to form more stable products. This results in the
decomposition of the intermediate to form 1,6-dioxa-6a-
chalcogenopentalene (35 and 37) via the nucleophilic attack
of hydroxyl function on the central electrophilic chalcogen (vide
infra), or it undergoes 1,6-addition followed by elimination to
afford the unsymmetrical 1-oxa-6,6aλ4-dichalcogenopentalenes
(33, 34, and 36) via the following mechanisms (Scheme 2) .
Singh and co-workers have reported a similar mechanism for
the formation of selenenate/tellurenate esters via intra-
molecular cyclization.22 However, the mechanism involving
the formation of cyclic monotelluride 38 is not clear. Oxidation
of 34 with m-CPBA at −78 °C gave 1-oxa-6,6aλ4-
diselenapentalene-6,6aλ4-dioxide 39 as a brown solid. In
comparison to 34, 1-oxa-6,6aλ4-diselenapentalene-6,6aλ4-diox-
ide 39 was found to be unstable at ambient temperature.
Product 39 decomposed slowly and led to the formation of 1-
oxa-6,6aλ4-diselenapentalene 34 even at −13 °C. Kice and
Reich and their co-workers have reported a similar observation
for five-membered 4,4-dimethyl-1,2-diselenolane-1-oxide,47,48
which was found to be unstable and decomposed even at
−20 °C. To our knowledge, 1-oxa-6,6aλ4-diselenapentalene-
6,6aλ4-dioxide 39 is the first example in which both of the
adjacent selenium(IV) atoms are part of the five-membered
heterocyclic ring. It is important to emphasize here that
compound 39 is expected to be a mixture of diastereomers,
similar to the chiral behavior of selenoxides.49 However, the
protons are significantly downfield and upfield shifted,
respectively, than the corresponding proton signals in the
starting material (7.26 and 10.16 ppm). That indicates the
delocalization of electron density in the cyclic systems.
Interestingly, in 1,6-dioxa-6a-selenapentalene 35, the vinylic
and the formyl proton signals merge to give an average signal at
8.70 ppm. This implies that the protons have more resemblance
to the vinylic proton than the formyl proton. It happens with
tellurapentalene 37 as well, and the corresponding protons
appear at 9.02 ppm. This indicates that both the oxygen atoms
are covalently bonded to selenium/tellurium atoms leading to
symmetrical structures that were further corroborated with X-
ray crystallographic and computational studies. In the case of
monotelluride 38, the vinyl protons appeared at 6.69 ppm and
the formyl proton at 9.95 ppm, which are significantly
downfield as compared to the 1-oxa-6,6aλ4-ditellurapentalene
36 (9.88 ppm). In the 1H NMR spectrum of compound 39, the
formyl proton appears at 9.70 ppm, which is significantly
downfield as compared to the corresponding 1-oxa-6,6aλ4-
diselenapentalene 34. In the cases of 33, 34, and 36, the formyl
carbons appeared at 182.5, 181.3, and 179.7 ppm, respectively,
which suggests that the formyl carbons are shifted to the upfield
region in going from S to Te. Compounds 35 and 37 show five
sets of peaks (C2C6, C3C5, C7C8) which further
indicate that the molecules are symmetrical, and the formyl
carbons are absent (Figure S12). In the case of 38, two peaks
appeared at 200.3 and 188.4 ppm corresponding to the formyl
carbon and the ketone carbonyl carbon, respectively.
The 77Se NMR spectrum of 34 showed two signals, one at
884 ppm and another broad one at 502.58 ppm, which could be
resolved into two signals at 502.37 and 502.79 ppm with a
coupling constant of 40 Hz (2J Se−H) (Figure S7). The broad
peak chemical shift (502.58 ppm) is downfield in comparison
to the chemical shift observed for related diselenide, bis(2,6-
diformyl-4-tert-butylphenyl)diselenide (458 ppm),21 but close
to that observed for tetramethyl-2,2′-diselanediylbis(5-(tert-
butyl)isophthalate) (519 ppm).22 The chemical shift at 884
ppm is closer to the chemical shift values observed for the
selenium atoms in selenazole like heterocycles,19,20 where the
arylselenium moiety is directly bonded to a nitrogen atom. The
diaryl selenoxide derivatives also have similar chemical shifts.50
Therefore, the signal at 884 ppm must be associated with the
selenium (central) which is coordinated to oxygen. The split
peaks at ∼503 ppm are associated with the peripheral selenium
and were further corroborated by theoretical studies (vide
infra). The splitting pattern of the peripheral selenium is
1
observation of clean H, 13C, and 77Se NMR spectra suggests
(Supporting Information) that compound 39 does not exist as
a mixtures of diastereomers. This could be due to the
prevalence of its achiral hydrated form, −C−Se(OH)2−
Se(OH)2−C−, in solution due to the inherent hygroscopic
behavior of selenoxides.49 Alternately, the possibility of its
structural isomer 39a cannot be ruled out. To compare the
structural features of tellurium systems (35 and 36) with
related aromatic derivatives, compound 40 was synthesized
following the procedure suggested in the literature.27 The
newly synthesized derivatives were fully characterized by
elemental analysis, common spectroscopic tools (1H, 13C,
77Se, and 125Te NMR and FT-IR spectroscopy) and mass
spectrometry (vide infra). The structures of compounds 33−38
were further corroborated by single crystal X-ray crystallog-
raphy (vide infra).
2
probably due to geminal J Se−H coupling. The coupling
constant observed for this splitting (40 Hz) is close to the
reported values (∼50−56 Hz) for the 2J Se−H coupling
constant, where Se is a part of heterocyclic ring and is coupled
with a vinylic hydrogen.51 This was further confirmed by
recording a proton decoupled 77Se NMR spectrum where the
split peaks appear as a single peak (Figure S8). Similarly, the
125Te NMR spectrum of 36 showed two signals, one at 1132
ppm and the other broad one at 366.73 ppm, which could be
resolved into two signals at 366.98 and 366.49 ppm with a
coupling constant of 77 Hz. The 125Te NMR chemical shift
observed at 366.73 ppm is significantly upfield shifted in
comparison to related ditelluride, bis[2-[1-(3,5-dimethylphen-
yl)-2-naphthyl]-4,5-dihydro-4,4-dimethyloxazole]ditelluride
(427 ppm).52 This is indicative of a more negative charge at the
terminal tellurium atom. The splitting of the peaks may be due
Spectral Features of 1-Oxa-6,6aλ4-dichalcogenopen-
1
talenes and 1,6-Dioxa-6a-chalcopentalenes. In the H
NMR spectra of 1-oxa-6,6aλ4-dichalcogenopentalenes 33, 34,
and 36, the vinyl protons appeared at 7.50, 8.37, and 9.88 ppm,
respectively, and the formyl protons appeared at 9.33, 9.45, and
9.97 ppm, respectively. The vinyl proton signals and formyl
2
to the J Te−H coupling. The coupling constant (77 Hz) is in
D
DOI: 10.1021/acs.joc.6b00173
J. Org. Chem. XXXX, XXX, XXX−XXX

The Journal of Organic Chemistry
Article
good agreement with the reported values for tellurophene (2J
Te−H; ∼87−100 Hz).53 The electronic environment around
selenium in 1,6-dioxa-6a-selenapentalene 35 is similar to the
electronic environment around the selenium center of the cyclic
arylselenenate esters.22 1,6-Dioxa-6a-tellurapentalene 37
showed 125Te NMR signal at 1982 ppm. The chemical shift
is upfield as compared to the related tellurenate ester 14 (2280
ppm).27 In the 125Te NMR spectrum of cyclic monotelluride
38, the signal observed at 774 ppm is significantly downfield
shifted in comparison to the reported value of [2-[1-(3,5-
d i m e t h y l p h e n y l ) - 2 - n a p h t h y l ] - 4 , 5 - d i h y d r o - 4 , 4 -
dimethyloxazole]phenyltelluride (670 ppm).52 This consider-
able downfield shift in 125Te NMR spectrum of 38 can be
attributed to the fact that here Te is part of a six-membered ring
and the delocalization of ring tellurium lone pair electrons into
the π-framework, such as in the resonance form 38(a′) (Figure
1).
respect to the systems containing its other lighter chalcogen
congeners (Supporting Information, page S53). Therefore,
increased electron density in the π* orbital of CO weakens
its double-bond character, which concomitantly reduces the
νCO through the conjugation effect when there is strong E···O
interaction. In cyclic telluride 38, the νCO of the formyl group
was observed in lower stretching frequency region (νCO
1519) as compared to νCO of the ketone carbonyl group
(νCO 1635) and as well as to the νCO of 33, 34, and 36. This
could be associated with the presence of stronger Te···
O(CHO) interaction in 38 and resonance delocalization as
described in Figure 1. The relatively higher νCO observed for
the ketone group in 38 with respect to the νCO of formyl
group in 36 and 38 is indicative of either weak or absence of
four-membered Te···O(keto) interaction, which is consistent
with the similar conclusion arrived from the studies on diaryl
ditelluride systems (vide infra).56
X-RAY CRYSTALLOGRAPHIC STUDY
Molecular Structure of Compound 33. The molecular
structure of compound 33 is depicted in Figure 2. The
■
Figure 1. Resonance structures of compound 38.
In 77Se NMR spectrum of compound 39, two expected 77Se
NMR signals were observed at 1190 and 1149.50 ppm
corresponding to the two selenium atoms which are in the
downfield region in comparison to the precursor 34 (884 and
502.58 ppm). The signal observed at 1149.50 ppm could be
resolved into two peaks, 1149.86 and 1149.14 ppm with a
coupling constant of 55 Hz. The 77Se NMR signal for Se
(selenium coordinated to oxygen) observed at 1190 ppm
(CDCl3) is close to the 77Se NMR chemical shift reported for a
seleninate ester54 (1204 ppm (DMSO-d6)) and of a seleninic
acid anhydride55 (1182 ppm (DMSO-d6). Generally, the 77Se
NMR signals for aryl cyclic selenenate esters are observed in
the range of 1350−1400 ppm. The observation of upfield
shifted 77Se NMR signals for 39, which are in the range
observed for seleninate esters, suggests that the possibility of
the alternate structure 39a is less likely. The 13C NMR signal of
formyl carbon is downfield (188.6 ppm) in comparison to the
corresponding signal for1-oxa-6,6aλ4-diselenapentalene 34
(181.3 ppm), while all three vinyl carbons are shifted to the
upfield region (164.9, 138.2, 137.4 ppm) compared to 34
(168.5, 142.3, 142.2 ppm).
In the FT-IR spectra of compounds 33, 34, and 36, the
carbonyl stretching frequencies (νCO) were observed at 1597,
1577, and 1534 cm−1, respectively. In general carbonyl groups
of α,β-unsaturated aldehyde/ketone compounds display νCO
stretches in the range of 1666−1685 cm−1. Therefore, the
significant decrease in νCO observed for 33, 34, and 36 is
indicative of the presence of a strong E···O interaction in these
compounds. Interestingly, the carbonyl stretching frequency
(νCO) of 1-oxa-6,6aλ4-dichalcogenopentalene systems de-
creases while going down the chalcogen group (S, Se, and
Te). It is in direct correlation with the decreasing E···O bond
distance (vide infra), in other words increasing E···O bond
strength, along the chalcogen group. Due to the propensity of
forming a strong E···O interaction while going down the
chalcogen group,15 the extent of donation of olefin π electrons
into π* orbital of CO is higher for the tellurium system with
Figure 2. Molecular structure of 33. Selected bond (Å) lengths and
bond angles (deg): S1−S2 2.099(1), S1···O1 2.489(3), S1−S2−O1
172.96(8), C1−S1 1.741(3), C3−S2 1.721(3), C8−O1 1.241(4).
geometry around the sulfur S1 atom is T-shaped with S1−S2−
O1 bond angle being 172.96(8)°, while the geometry around
S2 is V-shaped in which S1 is covalently bonded to S2 and
intramolecularly coordinated to O1 with S1···O1 bond distance
of 2.489(3) Å. The S1···O1 bond distance (2.489(3) Å) is
shorter than that reported for 2-(5-phenyl-1,2-dithiole-3-yl-
idene)cyclohexanone (2.555(8)) Å30 and slightly longer than
the 2,5-dimethyl-dithiofurophthene (2.41 Å)57 and 2,4-
diphenyl-dithiofurophthene (2.382(6) Å.58 However, the S−S
bond (2.099(1) Å) is significantly shorter than the correspond-
ing distance observed for 2-(5-phenyl-1,2-dithiole-3-yl-idene)-
cyclohexanone (2.126(4)) Å,30 2,5-dimethyl-dithiofurophthene
(2.12 Å), and 2,4-diphenyl-dithiofurophthene (2.106(3) Å). It
is also slightly longer than the sum of S−S covalent radii (2.04
Å).59 The planarity of the molecule is quite apparent from the
torsion angles observed for the atoms defining the tricyclic ring
system. All of the atoms forming fused five-membered rings are
nearly coplanar with the torsion angles O1−C8−C7−C6
(179.6(3)°), S2−C3−C2−C4 (178.4(3)°), S1−S2−C3−C2
(0.3(3)°), C1−C7−C8−O1 (1.06(5)°) except C5, for which
the torsional angle is C8−C7−C6−C5 is −156.3(3)°. Molecule
33 shows intermolecular hydrogen bonding (O···H) and S···S
van der Waals interactions in the solid state (Figure S39). The
O···H bond distances are 2.355(2) Å (O1···H3A) and 2.568(2)
E
DOI: 10.1021/acs.joc.6b00173
J. Org. Chem. XXXX, XXX, XXX−XXX

The Journal of Organic Chemistry
Article
Å (O1···H5A) with bond angles of C3−H3A···O1 (172.3(3)°)
and C5−H5A···O1 (148.1(2)°).
Molecular Structure of 34. The coordination geometry
around Se2 is V-shaped, while Se1 is approximately T-shaped
(Figure 3) with bond angles C1−Se2−Se1 and Se2−Se1−O1
Figure 4. Molecular structure of 36. Selected bond (Å) lengths and
bond angles (deg): Te1···O1 2.400(1), Te1A−Te2A 2.758(3), O1A−
Te1A−Te2A 159.6(6).
different modes of interactions. One of the telluriums, Te2
intermolecularly interacts with two tellurium atoms Te2 and
Te1, while tellurium Te1 intramolecularly interacts with only
one tellurium (Te2) of the neighboring molecule to construct a
Te4 rhombic core. The intermolecular interactions between
Te2A···Te1A and Te2A···Te2A are 3.959 and 3.975 Å (Figure
S41).
The structural elucidation of compounds 33, 34, and 36
shows that these molecules are nearly planar, except the carbon
C4/C5 which has translational freedom of motion. This
planarity can be interpreted in terms of the following resonating
structures a−c (Figure 5), a/b with SBI O···E−E/O−E···E or c
Figure 3. Molecular structure of 34. Selected bond (Å) lengths and
bond angles (deg): Se1···O1 2.392(11), Se1−C1 1.877(10), Se2−C7
1.839 (11), Se1−Se2 2.374(1), Se2−Se1−O1 168.4(1)°.
of 90.1(2)° and 168.4(1)°, respectively. The observed Se1−Se2
bond length of 2.374(1) Å is shorter than the respective Se−Se
distances in related heterocycles, 3,4-dimethyl-1-oxa-6,6aλ4-
diselena-2-azapentalene60 (2.444(2) Å) and 3,4-dimethyl-1-
thia-6,6aλ4-diselena-2-azapentalene (2.473(2) Å).60 However, it
is close to the distances reported for peri-substituted diselenides
such as naphtho[1,8-c,d][1,2]diselenole61 (2.364(5)Å), 2,7-di-
tert-butylnaphtho[1,8-c,d][1,2]diselenole62 (2.338(5) Å), and
2-tert-butylnaphtho[1,8-c,d][1,2]diselenole62 (2.339(1)Å). The
Se1···O1 bond length of 2.392(11) Å is longer than the
observed for 3,4-dimethyl-1-oxa-6,6aλ4-diselena-2-azapenta-
lene60 (Se−O (2.043(8) Å) and much shorter than those
observed for bis(o-formylphenyl)diselenide with Se···O dis-
tances are in the range of 2.720−2.751 Å. The sum of the van
der Waals radii of selenium and oxygen is 3.42 Å63 which
indicates a strong intramolecular Se···O interaction leading to
the formation of a tricyclic ring system in similar to the 1-oxa-
6,6aλ4-dithiapentalene 33. The torsion angles forming fused
five-membered rings are O1−C8−C6−C5 (180°), Se2−C7−
C2−C3 (180°), Se1−Se2−C7−C2 (0°), C1−C6−C8−O1
(0°), except C4, for which the torsion angle C8−C6−C5−C4
is −157°. Similar to 33, the two-dimensional packing diagram
of 34 shows weak Se···Se and O···H intermolecular interactions
forming a one-dimensional chain network (Figure S40). The
bond distances between Se1···Se1, Se2···Se2, and O···H are
3.529(9), 3.664(1), and 2.481(4) Å, respectively, and C7−
H7A···O1 bond angle is 178°. The Se···Se noncovalent bond
length is 3.529(9) Å, which is significantly shorter than the
reported for selenenate ester 9a (3.612(8) Å).22
Figure 5. Possible resonance structures of 1-oxa-6,6aλ4-dichalcogeno-
pentalenes, 33, 34, and 36.
with a covalent O−E−E bond. However, the X-ray structure
analysis (Table 1) indicates 1-oxa-6,6aλ4-diselenapentalene
(34) to be more planar than 1-oxa-6,6aλ4-dithiapentalene
(33) and 1-oxa-6,6aλ4-ditellurapentalene (36).
Molecular Structure of 35. The molecular structure of 35
is depicted in Figure 6. The asymmetric unit contains two
independent molecules with almost similar bond lengths and
bond angles. The geometry around selenium is T-shaped,
where the Se is covalently bonded with two oxygen atoms. The
Se−O bond distances of Se1−O1A (2.022(2) Å) and Se1−
Table 1. Comparison of X-ray Crystallographycally Obtained
in-Plane Torsion Angles for 33, 34, and 36
Molecular Structure of 36. The molecular structure of 36
is represented in Figure 4. The intramolecular Te1···O1
distance (2.400(1) Å) is significantly shorter than those
reported for a cyclic tellurenate ester 1427 (2.504 Å). The
E−E···O (E = S, Se, Te) bond angles decrease while going from
S to Te, with S(1)−S(2)−O(1), O(1)−Se(1)−Se(2), and
O(1a)−Te(1a)−Te(2a) bond angles being 172.96(8)°,
168.4(1)°, and 159.6(6)°, respectively.
torsion angles (deg)
torsion planes
33
34
36
C1−E1−E2−C7
E1−E2−C7−C2
E2−E1−C1−C2
E1−C1−C2−C7
E1−C1−C6−C8
C1−C6−C8−O1
−1.2(2)
0.3(3)
0.0(3)
0.0(6)
0.0(4)
0.0(8)
−0.0(7)
0.0(9)
−0(1)
4(2)
2.0(2)
−3(2)
7(4)
−2.2(4)
−1.4(4)
−1.1(5)
0(3)
The packing diagram of 36, revealed Te···Te and Te···O
intermolecular interactions. Interestingly, two telluriums have
−2(4)
F
DOI: 10.1021/acs.joc.6b00173
J. Org. Chem. XXXX, XXX, XXX−XXX

The Journal of Organic Chemistry
Article
the Te−O bond length of compound 40 (2.074(3)) and
reported values for tellurane 13b (2.133 and 2.173 Å).27
The packing diagram of 37 shows weak intermolecular Te···
O1 and C4−H4B···O2 interactions with bond distances of
3.473(5) and 2.596(5) Å, respectively (Figure S43).
Molecular Structure of 40. The geometry around the
tellurium atom is distorted T-shaped (Figure 8) with the bond
Figure 6. Molecular structure of 35. Selected bond (Å) lengths and
bond angles (deg): Se1−C1A 1.838(2), Se1−O1A 2.022(2), Se1−
O2A 2.036(2), O1A−Se1−O2A 164.92(8).
O2A (2.036(2) Å) are in good agreement with the reported
structure of 2739 (2.030 and 2.017 Å) but longer than Se−O
covalent bond length of 1.871(2) Å reported for a selenenate
ester.22 The Se1−C1A bond distance 1.838(2) Å is similar to
that reported for compound 27 (1.828 Å).39 The molecular
structure shows that two five-membered fused rings are nearly
coplanar with the torsion angles of Se1−C1A−C6A−C5A
−178.16(2)°, Se1−C1A−C2A−C3A −180°, O1A−C7A−
C2A−C3A 179.7(3)°, O2−C8A−C6A−C5A −180(3)°. The
packing diagram shows three different types of C−H···O
intermolecular hydrogen-bonding interactions which give rise
to a supramolecular assembly (Figure S42). The H···O bond
distances are O2A···H8BA−C8B 2.756(8) Å, O2B···H7AA−
C7A 2.528(7) Å, and O1B···H8AA−C8A 2.483(2) Å with the
bond angles 154.0(22)°, 152.8(16)°, and 154.1(16)° respec-
tively.
Figure 8. Molecular structure of 40. Selected bond distances (Å) and
bond angles (deg): Te1−O1 2.074(3), Te1···O3 2.548(3), Te1−C1
2.043(3), O3−Te−O1 149.9(10).
angle O1−Te−O3 of 149.9(10)° which is the good agreement
with reported tellurenate ester 1427 (149.8°), however, it is
significantly smaller than the respective bond angle observed
for the alicylic analogue 37 (154°). In 40, one of the oxygens is
directly bonded to the Te atom, and another one is
intramolecularly coordinated to tellurium. In 37, both the
oxygens are directly bonded (covalent bond) to the tellurium
atom. The Te1−O1 bond distance 2.074(3) is shorter than the
observed Te−O bond distances (2.174(5) and 2.162(5) Å) of
alicyclic 1,6-dioxa-6a-tellurapentalene 37. The intramolecular
Te···O3 bond distance (2.548(3) Å) is close to the distance
reported for related tellurenate ester 1427 (2.504 Å), however,
it is longer than the distance observed for 36 (2.40 Å) and
shorter than the distance observed for 38 (2.602(6) Å). The
C−Te bond distance 2.043(3) Å is slightly longer than C−Te
bond distance observed for 37 (2.020 (5) Å).
Molecular Structure of 37. 1,6-Dioxa-6a-tellurapentalene
37 (Figure 7) crystallizes in orthorhombic crystal system with
Molecular Structure of 38. In cyclic telluride 38 (Figure
9), the geometry around Te is V-shaped in which tellurium is
strongly intramolecularly coordinated with the formyl oxygen
(O2) and on the other side coordinated with ketonic oxygen
(O1) with Te···O2 and Te···O1 bond distances of 2.602(6) and
3.006(6) Å, respectively. The Te···O bond distance for the five-
membered ring is close to the value reported for related
Figure 7. Molecular structure of 37. Selected bond (Å) lengths and
bond angles (deg): Te−O1 2.174(5), Te−O2 2.162(5), O2−Te−O1
154.17(19).
chiral space group P212121, and the Flack parameter is 0.01(7).
The geometry around tellurium is T-shaped with O1−Te−O2
bond angles of 154.17(19)°. The Te−O bond lengths 2.174(5)
Å (Te−O1) and 2.162(5) Å(Te−O2) are in good agreement
with reported tellurapentalene 29,43 having Te−O bond
lengths of 2.130 and 2.124 Å. These are also very close to
Figure 9. Molecular structure of 38. Selected bond (Å) lengths and
bond angles (deg): Te···O2 2.602(6), Te−O1 3.006(6), Te−C13
2.075(7), O2···Te−C1 166.3(3), C13−Te−C1 93.1(3).
G
DOI: 10.1021/acs.joc.6b00173
J. Org. Chem. XXXX, XXX, XXX−XXX

The Journal of Organic Chemistry
Article
3,4,5,6,7,8-hexahydro-2H-9-telluraanthracene-1-carbaldehyde
2.591(5)Å.64 The crystal structure of compound 38 exhibits
intermolecular Te···H and C−H···O interactions with Te−H5B
and O1···H7A bond distances of 3.103(1) and 2.510(6) Å,
respectively, while the Te···H−C and C−H···O bond angles are
149.94° and 157.04°, respectively (Figure S44).
COMPUTATIONAL STUDIES
■
The Role of E···O Interaction on Chalcogenopentalene
Formation. As mentioned in the Synthesis section, the reactions of
16 with disodium dichalcogenides led to the formation of unsym-
metrical chalcogenopentalenes (33, 34, and 36) and symmetrical (35
and 37) chalcogenopentalenes. The competing pathways that lead to
the formation of unsymmetrical and symmetrical chalcogenopenta-
lenes are outlined in Scheme 2. The formation of the unsymmetrical
chalcogenopentalene is straightforward since the chalcogenolates have
a strong propensity to react with conjugated dienophiles via
intramolecular 1,6-conjugate addition reaction (Path (i)).65
Figure 11. Blue is the sulfur analogue, pinkis the selenium analogue,
and brown is the tellurium analogue.
Based on our previous observations on the intramolecular
cyclization of 2,6-disubstituted arylchalcogen compounds, we specu-
lated that the formation of the symmetrical chalcogenopentalenes
could occur via the intramolecular nucleophilic attack of the hydroxyl
group on the chalcogen center (Path (ii)).23 To our surprise, this
reaction occurs only for selenium and tellurium analogues but not for
the sulfur analogue. To understand these phenomena, we carried out a
conformational analysis on these systems using density functional
theory (DFT) calculations. For brevity, the sodium ion has been
exchanged with H+ in the calculations. All the possible conformers of
a−c ((syn, syn), (anti, syn), (syn, anti), and (anti, anti)) have been
optimized (Figure 10). Where (syn, syn) and (anti, anti)
and the Te analogue prefers the b (anti, syn) geometry. A close
observation of the geometries of b (anti, syn) and c (anti, anti)
conformers reveals that there is a disruption of the planarity of the
conjugated olefinic bonds in conformers b and corresponding c
conformers are highly planar along the conjugated olefinic bonds. The
deviation from the planarity in conformers b could be due to the strict
requirement of linearity of the donor−acceptor 3c-4e bond for the
effective interaction. The obstruction or steric collision of this linear
interaction elements by the second heteroatom donor leads to the
distortion of planarity of the π−π conjugated olefin bonds in
conformers b. It reveals that there is competition between the two
stabilizing forces, i.e., π−π extended conjugation and intramolecular
SBI. The π−π conjugation seems to be the most dominant
stabilization force for sulfur and selenium analogues, whereas the
secondary bonding O···E interaction dominates in the case of
tellurium analogue. The tellurium atom is more polarizable than the
sulfur and selenium atom that leads to the favorable Te···O interaction.
Therefore, the SBI must be sufficient enough to overcome the
destabilization that arises from the small disruption of the extended π-
conjugation system.
Figure 10. Possible conformers of chalcogenopentalenes.
This intramolecular stabilization of the intermediate does not stop
there, rather it activates the central tellurium toward intramolecular
nucleophilic attack of the hydroxyl function by making the central
tellurium more electrophilic. This leads to the formation of the
symmetrical 1,6-dioxa-6a-tellurapentalene. In case of the selenium
analogue, the energy of the conformer b is 1.80 kcal/mol higher than
the conformer c. It is probable that this conformer could be populated
at slightly elevated temperatures such that it leads to the formation of
symmetrical 1,6-dioxa-6a-selenapentalene. However, for the sulfur
analogue, electronic energy of conformation b is 4.94 kcal/mol higher
than that of the energy of the conformation c. This ΔE (= Ec − Eb) is
almost 3 times higher than that of the corresponding ΔE of the
selenium conformers. This leads to predominant formation unsym-
metrical thiapentalene 33 via exclusive thiolate addition reaction across
the conjugated olefine and does not lead to the formation of
symmetrical thiapentalene (sulfur analogue of 35 or 37).
conformation, both oxygens are either in a syn configuration or in
an anti configuration with respect to the carbon to which the central
chalcogen is bonded. Whereas, the (syn, anti) or (anti, syn)
configuration refers the conformers in which one oxygen is in syn
configuration and other one is in anti configuration with respect to the
carbon to which the central chalcogen is bonded. The calculated
relative electronic energies are provided in Table 2 and illustrated in
Figure 11.
Table 2. Relative Electronic Energies
E
(syn, syn) = a (anti, syn) = b (syn, anti) = b′ (anti, anti) = c
S
7.30
4.14
2.89
4.94
1.80
0
7.10
5.78
7.13
0
Se
0
Te
3.74
Natural Bond Orbital (NBO) Analysis. To gain more
information about the intramolecular E···O (E = S, Se, Te) interaction
in the newly synthesized organochalcogen compounds (33−40), DFT
calculations have been carried out using Gaussian 09 suite of
programs.66 The gas-phase optimized geometries obtained by DFT
calculations were well in conformity with the determined crystal
structures of the respective compounds, except compound 39 where
no crystal data is available (e.g., E···O distance, Table 3). The second-
order perturbation energies for intramolecular E···O interactions
obtained from NBO analysis67−69 for compounds 33−40 are listed in
Table 3. It indicates that the interaction energies in 1-oxa-6,6aλ4-
dichalcogenopentalenes 33, 34, and 36 increase while going from
sulfur to tellurium. In the case of 1-oxa-6,6aλ4-diselenapentalene-
6,6aλ4-dioxide (SeIV) 39, the intramolecular Se···O interactions energy
The apparent features of the relative energy are: (i) For S and Se
analogues, the relative energy of the conformers follows the order of a
> b′ > b > c and b′ > a > b > c, respectively, and (ii) for the Te
analogue, the relative energy of the conformers follows the order of b′
> c > a > b. Based on these observations we can infer that the
contribution of the hydroxyl functions E···O interaction toward
stabilization is of least importance, and this is evident from the
relatively higher energies of this conformation with respect to others.
This corroborates with our previous observations that hydroxyl
function are poorer electron donors than the carbonyl donors in terms
of donor−acceptor interactions.26,56 The conformers of our interests
are b and c, as S and Se analogues prefer the c (anti, anti) geometry
H
DOI: 10.1021/acs.joc.6b00173
J. Org. Chem. XXXX, XXX, XXX−XXX

The Journal of Organic Chemistry
Article
Table 3. Computed Geometry Parameters, NBO Second-Order Perturbation Energy and the Natural Charges Obtained for 33−
a
40
NPA charge
compd
rE−O/rE···O (Å) exp
rE···O/rE−O (Å) calcd
EE···O (kcal/mol)
qE
qE′
qO
33
34
36
2.489(3)
2.392(5)
2.40(2)
2.324
2.262
2.304
21.24
37.71
39.62
2.49
13.76
8.95
−
0.357
0.479
0.592
0.838
0.141
0.153
0.159
−
−0.587
−0.592
−0.617
−0.558
−0.589
−0.508
−0.640
−0.640
−0.670
−0.670
−0.582
b
b
3.006(6)
2.985
38
39
35
c
c
2.602(6)
2.488
-
2.633
2.034
2.033
2.171
2.173
2.486
1.138
0.836
1.039
2.036(2)
2.036(2)
2.174(5)
2.162(5)
2.548
−
−
0.959
0.875
−
−
37
40
17.84
2.074(3)
2.073
a
b
c
E = central chalcogen; E′ = peripheral chalcogen. Four-membered Te···O interaction. Five-membered Te···O interaction.
(8.95 kcal/mol) is less as compared to the corresponding 1-oxa-6,6aλ4-
diselenapentalene 34 (37.71 kcal/mol). We have previously noted that
Se···O interaction in the low-valent chalcogen SeII system is much
stronger than the corresponding interaction present in the high-valent
chalcogen SeIV system. This is due to the reduced polarizability of
selenium valence shell electrons in the latter system.23 Within NBO
model, the computed off-diagonal Fock matrix element F(i,j) or
resonance integral value for O···Se interaction in 39 is two times lower
than that of the corresponding F(i,j) value computed for compound
34 (Supporting Information, page S52). The weaker orbital overlap in
the former could be attributed to the increase of ionic character in the
O···Se bonding. It is further supported by the results obtained in AIM
analysis (vide infra). The plausible reason could be that although in the
higher oxidation state the acceptor orbital energy is significantly
lowered, the spatial extension is not enough for the strong orbital
interaction. For compound 38, both four and five-membered Te···O
interactions were observed. However, the Te1···O1 interaction energy
for four-membered interaction is small (2.49 kcal/mol) in comparison
to the Te1···O2 five-membered interaction energy (13.76 kcal/mol). It
indicates that the five-membered interaction is stronger than the four-
membered interaction. The charges on the central chalcogen and the
peripheral chalcogens were calculated using natural population analysis
(NPA). The NPA charges on the central chalcogen atoms (E) in
compounds 33, 34, and 36 were found to be +0.357, + 0.479 and
+0.592, respectively, and these are significantly greater than the
peripheral chalcogens (E′) (+0.141, + 0.153, and +0.158, respectively).
The NPA charges on central chalcogenes among 1-oxa-6,6aλ4-
dichalcogenopentalenes increase while going down the group from
sulfur (33; + 0.357) to tellurium (36; + 0.592). It is well established
that strong intramolecular coordination between E···O leads to a
significant increase in the positive charge on the central chalcogen.
Similarly, in cases of symmetrical structures, 1,6-dioxa-6a-chalcogeno-
pentalenes 35 and 37, the NPA charge on 1,6-dioxa-6a-tellurapenta-
lene 37 (+0.959) is greater than 1,6-dioxa-6a-selenapentalene 35
(0.836). The NPA charge of 1,6-dioxa-6a-tellurapentalene 37 (+0.959)
is also significantly higher than the cyclic monotelluride 38 (+0.838)
and aromatic system 40 (+0.875). Similarly, in case of 1-oxa-6,6aλ4-
diselenapentalene-6,6aλ4-dioxide 39, the NPA charges of selenium
(+1.138, + 1.039) are significantly higher than the corresponding 1-
oxa-6,6aλ4-diselenapentalene 34 (0.479, 0.153), which is expected
where both seleniums are bonded to oxygen atoms and in higher
oxidation state (IV) as compared to the 1-oxa-6,6aλ4-diselenapentalene
34 (SeII).
electron density (Table 4) is a signature of strong E···O intermolecular
interaction, and it revealed some of expected patterns. The electron
Table 4. Selected Topographical Features of E···O Bonds
Computed at the WTBS level for S, Se, and Te and
a
MPW1PW91/6-311g(d,p) Level for C, H, O
b
bcp
c
d
ρ
∇2ρ
H
bcp
compd
E···O/E−O
E···O/E−O
E···O/E−O
−0.0012
−0.0055
−0.0074
−0.0028
33
34
36
38
39
40
35
37
0.0471
0.1570
0.0567
0.1678
0.0575
0.0175
0.0422
0.1279
0.0293
9.4746
0.0006
0.0864
0.0852
−0.0147
−0.0206, −0.0820
0.0853, 0.0850
0.0712, 0.0715
0.2175, 0.2169
0.2545, 0.256
−0.0105, −0.0106
a
b
c
bcp = bond critical point. ρ = electron density at bcp. ∇2ρ =
Laplacian at bcp. H = total energy density.
d
density at the bond critical point observed in unsymmetrical
dichalcogenides increases from S to Te. The negative values of H
observed for E···O interaction support the contribution of covalent
character and in corollary with orbital interaction predicted by the
NBO analysis. Although E···O interaction is predominantly covalent,
the observation of positive value of Laplacian (∇2ρ) at the bcp implies
the fact that the considerable ionic contribution to the E···O
interaction cannot be ruled out. Especially, O···Te bond in 1,6-
dioxa-6a-tellurapentalene 37 has high ionic character which is in
agreement with lowest second-order perturbation energy obtained for
O···Te interaction in the NBO analysis of 37. Similar observation has
already been observed by Iwaoka and co-workers71 and Behera and co-
workers72 for Se···N intramolecular interactions. It has also been
observed for Se···O intramolecular interactions.67,73 In case of 39, the
value of total energy density (H) is positive (0.0006), and the
Laplacian (∇2ρ) at the bcp is very high which indicates predominant
ionic character arising due to the higher oxidation state of the selenium
in 39. In compound 38, no bcp could be located for the four-
membered Te···O(keto) interaction. Whereas, the five-membered
Te···O contact showed a bcp with an electron density (ρ) value of
0.042 au. It indicates the absence of four-membered Te···O interaction
which is in accordance with very low second-order perturbation energy
obtained in NBO analysis. Therefore, short Te···O contact observed in
both solid state and gas-phase structures for the four-membered
interaction could be a result of geometrical constraints rather than
orbital interaction. The analysis further correlated with our earlier
Atoms In Molecule Analysis (AIM). The electron density (ρ),
Laplacian (∇2ρ), and total energy density (H) at the bond critical
points (bcp) of E−O and E···O bonds were calculated using literature
procedure.70 The molecular graphs for the compounds 33−40 are
given in Figures S52 and S53. The observation of bond critical points
between chalcogen E (E = S, Se, and Te) and oxygen and high value of
I
DOI: 10.1021/acs.joc.6b00173
J. Org. Chem. XXXX, XXX, XXX−XXX

The Journal of Organic Chemistry
Article
observation on the absence of a weak intramolecular interaction in
four-membered Te···O system.56
Nucleus Induced Chemical Shift (NICS). In order to understand
the aromatic character of the two fused five-membered heterocyclic
rings, the NICS were calculated.74 One of the contributing forms of
the resonance structures, that is shown in Figure 12, illustrates the
synthesis of a series of chalcogenopentalenes. The potential
repulsive interaction among the juxtaposed chalcogen atoms
facilitates either nucleophilic attack of the hydroxyl function on
the central electrophilic chalcogen or 1,6-addition followed by
elimination to give 1,6-dioxa-6aλ4-chalcogenopentalenes and 1-
oxa-6,6aλ4-dichalcogenopentalenes, respectively. The formation
of 1-oxa-6,6aλ4−dichalcogenopentalenes is favored due to
strong propensity of chalcogenolates to react with conjugated
dienophiles via intramolecular 1,6-conjugate addition reaction.
However, the formation of 1,6-dioxa-6a-chalcogenopentalenes
35 and 37 results when the intramolecular E···O interaction is
significant and is comparable to the stabilization due to π−π
conjugation. Among 1-oxa-6,6aλ4-dichalcogenopentalenes, the
intramolecular E···O interaction is strongest for the tellurium
analogue 36, and as expected the CE character is more
dominant for S analogue 33. Although the NICS calculations
show some aromatic character in chalcogenopentalene systems,
this has to be rigorously evaluated in terms of their aromatic-
like chemical reactivity to further support this view. Hence,
these results will stimulate further attraction in the area of
chalcogenopentalene chemistry. The synthetic procedure and
the unique reactivity of the chalcogenolate intermediates
reported in this work can be a useful method to synthesis of
other substituted chalcogenopentalene derivatives for material
application.
Figure 12. 1-Oxa-6,6aλ4- and 1,6-dioxa-6a-chalcogenopentalenes rings.
aromatic 4n + 2 π-electron system where each peripheral chalcogen
contributes a pair of electrons to satisfy the Huckel’s rule of
̈
aromaticity. The other resonance structures involving no bond
resonance are shown in Figure 5. The isotropic chemical shifts
(Table 5) were computed for the ghost atom (bq) placed at the
middle of the rings a and b, NICS(0) (Figure 12). The calculation was
also done by placing the ghost atom 1 Å above the plane, NICSzz(1)
and below the plane, NICSzz(−1).
The isotropic chemical shift calculated in the plane includes the σ
contributions as well. Whereas the isotropic chemical shift computed 1
Å above or below provides an idea of the extent of π electron
delocalization and aromatic character. The isotropic chemical shifts
(NICSzz(1)) computed for the rings a and b in 1-oxa-6,6aλ4-
dichalcogenopentalenes (33, 34, 36) are not equal, which is in
accordance with asymmetric nature of these molecules. However, it is
worth noting that the isotropic chemical shift of five-membered b
heterocyclic ring in compounds 33 (−7.14), 34 (−7.50), 36 (−6.08) is
lower than the corresponding five-membered a ring. It could be due to
the dominant p characters of the S and Se lone pairs that participate in
delocalization within the b heterocyclic rings. The negative values and
considerable nearness to the isotropic chemical shift value calculated
for the benzene ring75 (−11.304 ppm) indicates that the b rings in 33,
34, and 36 have substantial aromatic characters. Similarly, for 1,6-
dioxa-6a-chalcogenopentalenes 35 and 37, due to symmetrical
structures of the heterocyclic rings a and b, the isotropic values
(NICSzz (1)) are equal, i.e., −7.21 ppm (35) and −6.23 ppm (37),
respectively. Compounds 39 and 40 have significantly higher isotropic
chemical shift than the isotropic shift values of chalcopentalene
derivatives. The molecular orbital diagrams generated using DFT
calculation also revealed that the certain HOMOs of the
chalcopentalene derivatives have delocalized electron density over
the all the atoms, for example, HOMO−11 of 35 and HOMO−3 of
37, of condensed heterocyclic ring system (Table S5).
EXPERIMENTAL SECTION
■
All the organochalcogen derivatives were synthesized under nitrogen
or argon atmosphere using standard Schlenk line techniques. Solvents
were purified and dried by standard procedures and were freshly
distilled prior to use.76 All the chemicals used were reagent grade and
were used as received. Melting points were recorded in capillary tubes.
1
The H (400 MHz/500 MHz), 13C (100/125 MHz), 77Se (76.4/95.4
MHz), and 125Te (126.3/157.8 MHz) NMR spectra were recorded in
CDCl3 solvent using NMR spectrometer. Chemical shifts cited were
referenced with respect to TMS for (1H and 13C) as an internal
standard and Me2Se (for 77Se) and Me2Te (for 125Te) as an external
standards. Elemental analysis was performed on elemental analyzer.
The IR spectra were recorded in the range of 400−4000 cm−1 by using
KBr pellets for solid samples on a FT-IR spectrometer. Mass spectral
(MS) studies were performed by using a Q-TOF Micro mass
spectrometer with electrospray ionization (ESI) mode analysis. In the
case of isotopic patterns, the value is given for the most abundant peak.
In column chromatography, silica gel was used as a stationary phase,
whereas petroleum ether (60−80 °C) and ethyl acetate were used as
mobile phase.
Synthesis of 2-Chloro-1-formyl-3-hydroxymethylenecyclo-
hexene (16).45 To a cold solution of DMF (20 mL, 0.27 mol) in
CH2Cl2 (20 mL), POCl3 (18.5 mL, 0.115 mol) was added dropwise at
0 °C. After 30 min, cyclohexanone (5 g, 0.05 mol) was added at the
same temperature. The resulting mixture was refluxed for 3 h at 58−60
°C. The reaction mixture was then cooled using ice bath, poured on
CONCLUSIONS
■
In conclusion, 2-chlorocyclohex-1-ene-1,3-dicarbaldehyde (16′)
and its enol form 2-chloro-1-formyl-3-hydroxymethylenecyclo-
hexene (16) serve as excellent precursors for the one-pot
Table 5. Comparison of Isotropic Chemical Shifts Obtained for the Ghost Atom (bq) at the Center: In Plane NICS(0), Out of
Plane NICSzz(1), and NICSzz(−1)
compd
33
NICS(0), ppm
NICSzz(1), ppm
−7.141
NICSzz(−1), ppm
−7.437
−10.627
−10.172
−8.790
−9.298
−8.430
−2.485
−4.406
−8.960
−5.552
−7.049
−7.263
−9.307
−8.424
−0.686
−2.927
−
−5.378
−6.276
−6.029
−7.208
−6.227
−3.197
−2.477
−
−5.504
−6.434
−6.111
−7.602
−6.575
−2.267
−2.477
−
34
36
−7.500
−6.075
−7.205
−6.227
−3.221
−2.485
−11.304
−7.879
−6.375
−7.599
−6.576
−3.261
−2.485
−11.304
35
37
39
40
Benzene
J
DOI: 10.1021/acs.joc.6b00173
J. Org. Chem. XXXX, XXX, XXX−XXX

The Journal of Organic Chemistry
Article
crushed ice, and kept for 1−2 h. The resulting yellow precipitate was
collected and washed with cold water (partially soluble in water) to
remove the acidic impurities and finally washed with cold ethanol.
Yield: 8.0 g, (91%); mp 126−128 °C (lit.125−127 °C); 1H NMR (400
MHz, CD3OD): δ(ppm) 10.16 (s, 1H) 7.26 (s, 1H), 2.57−2.41 (m,
2H), 1.67−1.57 (m, 2H); FT-IR (KBr) υCO, 1603; CH−OH, 3198
cm−1. MS-ESI: m/z calcd for C8H10ClO2: 173.0, found: 173.1 [M +
H]+.
into ice−water mixture. The organic layer was extracted with
dichloromethane and washed with cold water twice, dried over
Na2SO4, and concentrated under vacuum to get a deep red-orange
liquid. The liquid was purified by column chromatography (2−10%
ethyl acetate-petroleum ether). Similarly, in the case of Na2Te2
reaction, four fractions were obtained. The first fraction isolated was
1-oxa-6,6aλ4-ditellurapentalene 36 as red colored solid, and the second
fraction was 1,6-dioxa-6a-tellurapentalene 37 as yellowish orange
colored solid. The third fraction was cyclic monotelluride 38 as a dark
red solid, and fourth one was the unreacted starting material 16. The
crystals were obtained from dichloromethane-n-hexane by slow
evaporation.
Synthesis of 1-Oxa-6,6aλ4-dithiapentalene 33. A stirred
solution of disodium disulfide [prepared in situ by the reaction of
sodium (0.84 g, 0.037 mol) and sulfur (1.16 g, 36.5 mmol) in dry THF
in the presence of catalytic amount of naphthalene]77 was treated with
16 (5.92 g, 34.4 mmol) and HMPA (14.6 mL) at room temperature.
The reaction mixture was stirred at room temperature for 1 h and then
refluxed for 4 h. After cooling, the reaction mixture was poured into
water, and the organic layer was extracted with dichloromethane,
washed twice with water, and dried over Na2SO4. The resulting
solution was concentrated under vacuum to get as a yellow orange
liquid. The liquid was purified by column chromatography (1−3%
ethyl acetate-petroleum ether) to get 33 as a yellow solid which was
recrystallized from slow evaporation of ethyl acetate-n-hexane to give a
1-Oxa-6,6aλ4-ditellurapentalene (36). Red solid; yield: 0.24 g
1
(5%), mp 116−118 °C; H NMR (400 MHz, CDCl3): δ(ppm) 9.97
(s, −CHO, 1H), 9.88 (s, −CHO, 1H), 3.16−3.13 (t, 2H, J = 5.9 Hz),
2.53−2.51 (t, 2H, J = 6.0 Hz), 2.04−1.96 (m, 2H); 13C NMR (125.8
MHz, CDCl3): δ 22.6, 28.0, 35.7, 134.5, 135.2, 155.5, 164.8, 179.7;
125Te NMR (157.8 MHz, CDCl3): δ 1132, 366.73 (2J Te−H 77 Hz);
FT-IR (KBr) υ 664, 1058, 1177, 1299, 1396, 1432, 1534, 1632, 2920.
HRMS-ESI: m/z calcd for C8H9Te2O: 380.8778; found: 380.8761 [M
+ H]+.
1
yellow color needles. Yield: 2.31g (37%), mp 108−109 °C; H NMR
1,6-Dioxa-6a-tellurapentalene (37). Yellowish orange solid; yield:
0.75 g (20%), mp 125−127 °C; 1H NMR (400 MHz, CDCl3):
δ(ppm) 9.02 (s, 2H), 2.91−2.88 (t, 4H, J = 5.9 Hz), 2.03−1.97
(quintet, 2H, J = 6.2 Hz); 13C NMR (100 MHz, CDCl3): δ 23.0, 24.9,
123.0, 135.2, 170.4, 172.4; 125Te NMR (126 MHz, CDCl3): δ 1982;
FT-IR (KBr) υ 656, 644, 1177, 1218, 1236, 1410, 1434, 1533, 1656,
2922, cm−1. HRMS-ESI: m/z calcd for C8H9TeO2: 266.9665, found:
266.9657 [M + H]+. Anal. calcd for C8H9TeO2: C, 36.43; H, 3.06;
found C, 36.59; H, 2.91.
(400 MHz, CDCl3): δ(ppm) 9.33 (s, −CHO, 1H), 7.50 (s, 1H),
2.85−2.81 (m, 2H), 2.71−2.68 (t, 2H, J = 6 Hz), 1.93−1.88 (m, 4H);
13C NMR (CDCl3): δ 21.1, 24.8, 28.3, 121.0, 137.3, 137.4, 163.2,
182.5; FT-IR (KBr) υ 812, 1064, 1369, 1418, 1440, 1597, 2933, 3010
cm−1. HRMS-ESI: m/z calcd for C8H9S2O: 185.0095, found: 185.0098
[M + H]+.
Synthesis of 1-Oxa-6,6aλ4-diselenapentalene 34. A solution
of disodium diselenide [generated in situ from the mixture of sodium
(0.07 g, 3 mmol) and selenium (0.24 g, 3.0 mmol) in dry THF in the
presence of catalytic amount of naphthalene]77 was treated with 16
(0.50 g, 2.9 mmol) in HMPA (1.19 mL, 6.67 mmol) at room
temperature. The reaction mixture was stirred at room temperature for
1 h and then refluxed for 6 h. After cooling, the reaction mixture was
poured into water. The organic layer was extracted with dichloro-
methane and washed twice with water, dried over Na2SO4, and
concentrated under vacuum to get an orange liquid. The liquid was
purified by column chromatography (2−5% ethyl acetate-petroleum
ether) to get four fractions. The first fraction was 1-oxa-6,6aλ4-
diselenapentalene 34 as an orange solid. The second fraction was 1,6-
dioxa-6a-selenapentalene 35 as a yellow colored solid, and the third
fraction was as a maroon colored sticky solid which could not be
characterized. The compounds were recrystallized from ethyl acetate
and n-hexane.
Cyclic monotelluride 38. Dark red solid; Yield: 0.33 g (7%), mp
1
179−181 °C; H NMR (400 MHz, CDCl3): δ(ppm) 9.94 (s, 1H),
6.68 (s, 1H), 2.89−2.85 (t, 2H, J = 5.5 Hz), 2.72−2.61 (m, 4H), 2.16−
2.09 (quintet, 4H, J = 5.9 Hz), 2.04−1.91 (m, 2H); 13C NMR (100
MHz, CDCl3): δ 22.0, 22.9, 34.0, 36.1, 37.4, 131.7, 137.2, 141.1, 145.3,
152.1, 188.4, 200.3; 125Te NMR (126 MHz, CDCl3): δ 774; FT-IR
(KBr) υ 705, 982, 987, 1171, 1188, 1415, 1435, 1519, 1606, 1635,
2939; MS-ESI m/z calcd for C14H15TeO2: 345.01, found: 345.01 [M +
H]+. Anal. calcd for C14H14TeO2: 49.19; H, 4.13; found C, 49.63; H,
4.41.
Synthesis of 1-Oxa-6,6aλ4-diselenapentalene-6,6aλ4-dioxide
39. A solution of m-chloroperbenzoic acid (0.25 g, 0.72 mmol) in dry
dichloromethane (7 mL) was cooled to −73 °C. To the above was
added 1-oxa-6,6aλ4-diselenapentalene 34 (0.10 g, 0.36 mmol), and the
reaction was allowed to stir at this temperature for 35 to 40 min. Then
the reaction mixture was poured into the solution containing saturated
NaHCO3 and dichloromethane. The organic layer was extracted with
dichloromethane, washed thrice with water, and dried over Na2SO4.
The filtrate was concentrated and washed with hexane to get 39 as an
1-Oxa-6,6aλ4-diselenapentalene (34). Orange solid; yield: 0.18 g
(21%), mp 94−96 °C; 1H NMR (400 MHz, CDCl3): δ(ppm) 9.45 (s,
−CHO, 1H), 8.37 (s, 1H), 2.92−2.89 (t, 2H, J = 5.8 Hz), 2.63−2.60
(t, 2H, J = 5.8 Hz), 1.99−1.93 (m, 2H); 13C NMR (100 MHz,
CDCl3): δ 22.1, 26.0, 31.3, 127.4, 142.2, 142.3, 168.5, 181.2, 181.3;
77Se NMR (95.4 MHz, CDCl3): δ 884, 502.58 (2J Se−H, 40 Hz); FT-
IR (KBr) υ 820, 857, 1356, 1412, 1428, 1577, 2936, 3017 cm−1.
HRMS-ESI: m/z calcd for C8H9Se2O: 280.8984, found: 280.8986 [M
+ H]+; Anal. calcd for C8H8Se2O: C, 34.55; H, 2.90; found C, 34.55,
H, 2.75.
1
orange yellow solid. Yield: 0.02 g (15%), mp 126−128 °C; H NMR
(400 MHz, CDCl3): δ(ppm) 9.70 (s, −CHO, 1H), 6.95 (s, 1H),
3.00−2.81 (m, 2H), 2.77−2.60 (m, 2H), 2.17−1.93 (m, 2H); 13C
NMR (100.6 MHz, CDCl3): δ 22.3, 26.1, 35.6, 130.7, 137.4, 138.2,
164.9, 188.6; 77Se NMR (76.4 MHz, CDCl3): δ 1190, 1149.49 (2J Se−
H, 55 Hz); HRMS-ESI: m/z calcd for C8H9Se2O3: 312.8882, found:
312.8889 [M + H]+.
1,6-Dioxa-6a-selenapentalene (35). Yellow solid; yield: 0.16 g
1
Computational Details. All calculations were performed with
Gaussian 09 program.66 Geometries were fully optimized at
MPW1PW91 method by using Lanl2dz(d,p) basis set for sulfur,
selenium, and tellurium and 6-311g(d,p) level for the rest of the atom.
The NBO67−69 and NICS74 analyses for all the systems 33−39 were
performed at MPW1PW91 method by using TZP-DKH basis set for
sulfur, selenium, and tellurium and 6-311g(d,p) level for the rest of the
atom. The AIM66,79−81 analysis was performed with AIM82 at
MPW1PW91 level of theory with wtbs basis set for S, Se, and Te
and 6-311g(d,p) level for remaining atoms.
X-ray Crystal Structure Determination. The single crystal X-ray
diffraction measurements for compounds and 33−38 and 40 were
performed on a diffraction measurement device with graphite
monochromated Mo Kα radiation (λ = 0.7107 Å). The structures
(26%), mp 99−101 °C; H NMR (400 MHz, CDCl3): δ (ppm) 8.70
(s, 2H), 2.85−2.82 (t, 4H, J = 5.9 Hz), 2.01−1.97 (m, 2H); 13C NMR
(100 MHz, CDCl3): 22.6, 23.0, 117.8, 167.3, 173.4; 77Se NMR (76.4
MHz, CDCl3): δ 1379; HRMS-ESI: m/z calcd for C8H9SeO2:
216.9763; found: 216.9771 [M + H]+. FT-IR (KBr) υ 665, 1190, 1227,
1325, 1421, 1437, 1542, 2836, 2866 2937 cm−1. Anal. calcd for
C8H8SeO2: C, 44.67, H, 3.75; found: C, 44.54, H, 3.41.
Synthesis of 1-Oxa-6,6aλ4-ditellurapentalene 36. A stirred
solution of disodium ditelluride [generated in situ by the mixture of
sodium (0.33 g, 14 mmol) and tellurium (1.82 g, 14.3 mmol) in dry
THF in the presence of catalytic amount of naphthalene]77,78 was
reacted with 16 (2.5 g, 14 mmol) in HMPA (5.7 mL) at room
temperature. The mixture was stirred for 1 h at room temperature and
then refluxed for 6 h. After cooling, the reaction mixture was poured
K
DOI: 10.1021/acs.joc.6b00173
J. Org. Chem. XXXX, XXX, XXX−XXX

The Journal of Organic Chemistry
Article
were determined by routine heavy-atom method using SHELXS 9783
and refined by full-matrix least-squares with the nonhydrogen atom
anisotropic and hydrogen atoms with fixed isotropic thermal
parameters of 0.07 Å by means of SHELXS 97 program.84 The
heteroatom hydrogens were located from difference electron density
map, and the rest was fixed at predetermined positions. Scattering
factors were from common sources.85 A riding model was chosen for
refinement. The structure refinement parameters for compounds 33−
38 and 40 are given in Tables S1 and S2. CCDC-1012745 (33),
CCDC-1012749 (34), CCDC-1012744 (35), CCDC- 1012746 (36),
CCDC-1012748 (37), CCDC-1012747 (38), and CCDC-1012750
(40) contain the supplementary crystallographic datafor this paper.
These data can be obtained free of charge from The Cambridge
Crystallographic Data Centre via www.ccdc.cam.ac.uk/data_request/
cif.
(10) Freudendahl, D. M.; Shahzad, S. A.; Wirth, T. Eur. J. Org. Chem.
2009, 2009, 1649.
(11) Kornienko, A.; Banerjee, S.; Kumar, G. A.; Riman, R. E.; Emge,
T. J.; Brennan, J. G. J. Am. Chem. Soc. 2005, 127, 14008.
(12) Zhang, H.; Wang, D.; Mohwald, H. Angew. Chem., Int. Ed. 2006,
̈
45, 748.
(13) Back, T. G.; Moussa, Z.; Parvez, M. Angew. Chem., Int. Ed. 2004,
43, 1268.
(14) Engman, L.; Stern, D.; Cotgreave, I. A.; Andersson, C. M. J. Am.
Chem. Soc. 1992, 114, 9737.
(15) Mukherjee, A. J.; Zade, S. S.; Singh, H. B.; Sunoj, R. B. Chem.
Rev. 2010, 110, 4357.
(16) Saiki, T.; Goto, K.; Okazaki, R. Angew. Chem., Int. Ed. Engl.
1997, 36, 2223.
(17) Kersting, B.; DeLion, M. Z. Naturforsch., B: J. Chem. Sci. 1999,
54, 1042.
ASSOCIATED CONTENT
■
(18) Kersting, B. Z. Naturforsch. 2002, 57b, 1115−1119.
(19) Zade, S. S.; Panda, S.; Tripathi, S. K.; Singh, H. B.;
Wolmershauser, G. Eur. J. Org. Chem. 2004, 18, 3857.
(20) Roy, G.; Mugesh, G. J. Am. Chem. Soc. 2005, 127, 15207.
(21) Zade, S. S.; Panda, S.; Singh, H. B.; Sunoj, R. B.; Butcher, R. J. J.
Org. Chem. 2005, 70, 3693.
(22) Selvakumar, K.; Singh, H. B.; Butcher, R. J. Chem. - Eur. J. 2010,
16, 10576.
(23) Singh, V. P.; Singh, H. B.; Butcher, R. J. Chem. - Asian J. 2011, 6,
1431.
(24) Parnham, M. J.; Biederman, J.; Bittner, C.; Dereu, N.; Leyck, S.;
Wetzig, H. Agents Actions 1989, 27, 306.
(25) McNeil, N. M. R.; Matz, M. C.; Back, T. G. J. Org. Chem. 2013,
78, 10369.
(26) Selvakumar, K.; Singh, H. B.; Goel, N.; Singh, U. P.; Butcher, R.
J. Dalton Trans. 2011, 40, 9858.
(27) Selvakumar, K.; Singh, H. B.; Goel, N.; Singh, U. P.
Organometallics 2011, 30, 3892.
S
* Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.joc.6b00173.
1H, 13C, 77Se and 125Te NMR spectra, MS (ESI) or
HRMS (ESI), DFT-optimized geometries, ORTEP
diagrams, unit cell packing diagrams and tables of crystal
refinement data for compounds 33, 34, 35, 36, 37, 38,
and 40 (PDF)
Crystallographic data for 33 (CIF)
Crystallographic data for 34 (CIF)
Crystallographic data for 35 (CIF)
Crystallographic data for 36 (CIF)
Crystallographic data for 37 (CIF)
Crystallographic data for 38 (CIF)
Crystallographic data for 40 (CIF)
(28) Geiger, T.; Benmansour, H.; Fan, B.; Hany, R.; Nuesch, F.
̈
Macromol. Rapid Commun. 2008, 29, 651.
AUTHOR INFORMATION
■
(29) Beer, R. J. S.; Poole, A. J. Tetrahedron Lett. 1972, 13, 1835.
(30) Pinel, R.; Mollier, Y.; Liaguno, E. C.; Paul, I. C. J. Chem. Soc. D
1971, 1352.
(31) Reid, D. H.; Webster, R. G. J. Chem. Soc., Perkin Trans. 1 1972,
1447.
(32) Minkin, V. I.; Minyaev, R. M. Chem. Rev. 2001, 101, 1247.
(33) Reid, D. H. Organic Compounds of Sulphur, Selenium, and
Tellurium; The Chemical Society: London, 1970; Vol. I, pp 321−335.
(34) Chuang, Y.-C.; Li, Y.-W.; Hsu, I. J.; Lee, G.-H.; Wang, Y. Inorg.
Chem. 2013, 52, 10958.
(35) Dingwall, J. G.; Reid, D. H.; Symon, J. D. J. Chem. Soc. C 1970,
2412.
Corresponding Author
*E-mail: chhbsia@chem.iitb.ac.in.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
H.B.S. is grateful to the Department of Science and Technology
(DST), New Delhi (India), for J C Bose Fellowship. P.R.P. is
thankful to Department of Chemistry, IIT Bombay for a
teaching assistantship and to Dr. Sagar Sharma for help in
computational studies.
(36) Hansen, L. K.; Hordvik, A. J. Chem. Soc., Chem. Commun. 1974,
0, 800.
(37) Ingold, K. U.; Reid, D. H.; Walton, J. C. J. Chem. Soc., Perkin
Trans. 2 1982, 431.
(38) Christie, R. M.; Reid, D. H.; Walker, R.; Webster, R. G. J. Chem.
Soc., Perkin Trans. 1 1978, 195.
DEDICATION
■
Dedicated to Professor Vladimir I. Minkin on the occasion of
his 80th birthday.
(39) Reid, D. H.; Webster, R. G. J. Chem. Soc., Perkin Trans. 1 1975,
775.
(40) Dingwall, J. G.; Dunn, A. R.; Reid, D. H.; Wade, K. O. J. Chem.
Soc., Perkin Trans. 1 1972, 1360.
REFERENCES
■
(1) Fujihara, H.; Mima, H.; Furukawa, N. J. Am. Chem. Soc. 1995,
117, 10153.
(41) Saethre, L. J.; Martensson, N.; Svensson, S.; Malmquist, P. A.;
Gelius, U.; Siegbahn, K. J. Am. Chem. Soc. 1980, 102, 1783.
(42) Reid, D. H.; Webster, R. G. J. Chem. Soc., Chem. Commun. 1972,
1283.
(43) Detty, M. R.; Luss, H. R. J. Org. Chem. 1983, 48, 5149.
(44) Detty, M. R.; Perlstein, J. H. Chalcogenopentalene Compounds
in Electrophotography. U.S. Patent 4450217, May 22, 1984.
(45) Reynolds, G. A.; Drexhage, K. H. J. Org. Chem. 1977, 42, 885.
(46) Furukawa, N.; Kobayashi, K.; Sato, S. J. Organomet. Chem. 2000,
611, 116.
(2) Klapotke, T. M.; Krumm, B.; Polborn, K. J. Am. Chem. Soc. 2004,
126, 710.
̈
(3) Nakanishi, W.; Hayashi, S.; Itoh, N. J. Org. Chem. 2004, 69, 1676.
(4) Sarma, B. K.; Mugesh, G. J. Am. Chem. Soc. 2005, 127, 11477.
(5) Sarma, B. K.; Mugesh, G. Chem. - Eur. J. 2008, 14, 10603.
(6) Back, T. G. Organoselenium Chemistry: A Practical Approach;
Oxford University Press: Oxford, U.K., 1999.
(7) Nishibayashi, Y.; Uemura, S. Top. Curr. Chem. 2000, 208, 201.
(8) Back, T. G.; Kuzma, D.; Parvez, M. J. Org. Chem. 2005, 70, 9230.
(9) Khokhar, S. S.; Wirth, T. Angew. Chem., Int. Ed. 2004, 43, 631.
L
DOI: 10.1021/acs.joc.6b00173
J. Org. Chem. XXXX, XXX, XXX−XXX

The Journal of Organic Chemistry
Article
(47) Kice, J. L.; Kang, Y. H.; Manek, M. B. J. Org. Chem. 1988, 53,
2435.
(48) Reich, H. J.; Hoeger, C. A.; Willis, W. W. J. Am. Chem. Soc.
(75) Zywietz, T. K.; Jiao, H.; Schleyer, P. v. R.; de Meijere, A. J. Org.
Chem. 1998, 63, 3417.
(76) Perrin, D. D.; Armargo, W. L. F.; Perrin, D. R. Purification of
Laboratory Chemicals, 4th ed.; Butterworth-Heinemann: Oxford, U.K.,
1996.
(77) Thompson, D. P.; Boudjouk, P. J. Org. Chem. 1988, 53, 2109.
(78) Engman, L.; Persson, J. J. Organomet. Chem. 1990, 388, 71.
(79) Bader, R. F. W. Atoms in Molecules: A Quantum Theory; Oxford
University Press: New York, 1990.
(80) Popelier, P. Atoms in Molecules: An Introduction; Prentice Hall:
Upper Saddle River, NJ, 2000.
(81) Matta, C. F.; Boyd, R. J. The Quantum Theory of Atoms in
Molecules: From Solid State to DNA and Drug Design; Wiley-VCH:
Weinheim, 2007.
(82) Biegler-Konig, F.; Schonbohm, J.; Bayles, D. J. Comput. Chem.
2001, 22, 545.
1982, 104, 2936.
(49) Shimizu, T.; Kobayashi, M.; Kamigata, N. Bull. Chem. Soc. Jpn.
1988, 61, 3761.
(50) Hayashi, S.; Nakanishi, W.; Furuta, A.; Drabowicz, J.; Sasamori,
T.; Tokitoh, N. New J. Chem. 2009, 33, 196.
(51) Rusakov, Y. Y.; Krivdin, L. B.; Potapov, V. A.; Penzik, M. V.;
Amosova, S. V. Magn. Reson. Chem. 2011, 49, 389.
(52) Kandasamy, K.; Kumar, S.; Singh, H. B.; Wolmershauser, G.
̈
Organometallics 2003, 22, 5069.
(53) Rusakov, Y. Y.; Krivdin, L. B.; Osterstrom, F. F.; Sauer, S. P. A.;
Potapov, V. A.; Amosova, S. V. Phys. Chem. Chem. Phys. 2013, 15,
13101.
(54) Tripathi, S. K.; Sharma, S.; Singh, H. B.; Butcher, R. J. Org.
Biomol. Chem. 2011, 9, 581.
(55) Yu, S.-C.; Borchert, A.; Kuhn, H.; Ivanov, I. Chem. - Eur. J. 2008,
14, 7066.
(56) Tripathi, S. K.; Patel, U.; Roy, D.; Sunoj, R. B.; Singh, H. B.;
(83) Sheldrick, G. M. SHELXS-97, Program for Crystal Structure
Solution; University of Gottingen: Gottingen, Germany, 1997.
̈
̈
(84) Sheldrick, G. M. Program for Crystal Structure Solution;
University of Gottingen: Gottingen, Germany, 1997.
̈
̈
(85) International Tables for X-ray Crystallography; Kynoch Press:
Birmingham, 1974; Vol. 4.
Wolmershauser, G.; Butcher, R. J. J. Org. Chem. 2005, 70, 9237.
̈
(57) Mammi, M.; Bardi, R.; Traverso, G.; Bezzi, S. Nature 1961, 192,
1282.
(58) Hordvik, A.; Sletten, E.; Sletten, J. Acta Chem. Scand. 1969, 23,
1377.
(59) Cordero, B.; Gomez, V.; Platero-Prats, A. E.; Reves, M.;
Echeverria, J.; Cremades, E.; Barragan, F.; Alvarez, S. Dalton Trans.
2008, 2832.
(60) Allen, C.; Boeyens, J. C. A.; Briggs, A. G.; Denner, L.; Markwell,
A. J.; Reid, D. H.; Rosea, B. G. J. Chem. Soc., Chem. Commun. 1987, 0,
967.
(61) Aucott, S. M.; Milton, H. L.; Robertson, S. D.; Slawin, A. M. Z.;
Woollins, J. D. Heteroat. Chem. 2004, 15, 530.
(62) Fuller, A. L.; Knight, F. R.; Slawin, A. M. Z.; Woollins, J. D. Eur.
J. Inorg. Chem. 2010, 2010, 4034.
(63) Bondi, A. J. Phys. Chem. 1964, 68, 441.
(64) Lamotte, J.; Campsteyn, H.; Dupont, L.; Vermeire, M. Cryst.
Struct. Commun. 1977, 6, 749.
(65) Khatik, G. L.; Kumar, R.; Chakraborti, A. K. Org. Lett. 2006, 8,
2433.
(66) Frisch, M. J.; Trucks, G. W.; Schlegel, H. B.; Scuseria, G. E.;
Robb, M. A.; Cheeseman, J. R.; Scalmani, G.; Barone, V.; Mennucci,
B.; Petersson, G. A.; Nakatsuji, H.; Caricato, M.; Li, X.; Hratchian, H.
P.; Izmaylov, A. F.; Bloino, J.; Zheng, G.; Sonnenberg, J. L.; Hada, M.;
Ehara, M.; Toyota, K.; Fukuda, R.; Hasegawa, J.; Ishida, M.; Nakajima,
T.; Honda, Y.; Kitao, O.; Nakai, H.; Vreven, T.; Montgomery, J. A., Jr.;
Peralta, J. E.; Ogliaro, F.; Bearpark, M.; Heyd, J. J.; Brothers, E.; Kudin,
K. N.; Staroverov, V. N.; Kobayashi, R.; Normand, J.; Raghavachari, K.;
Rendell, A.; Burant, J. C.; Iyengar, S. S.; Tomasi, J.; Cossi, M.; Rega,
N.; Millam, J. M.; Klene, M.; Knox, J. E.; Cross, J. B.; Bakken, V.;
Adamo, C.; Jaramillo, J.; Gomperts, R.; Stratmann, R. E.; Yazyev, O.;
Austin, A. J.; Cammi, R.; Pomelli, C.; Ochterski, J. W.; Martin, R. L.;
Morokuma, K.; Zakrzewski, V. G.; Voth, G. A.; Salvador, P.;
̈
Dannenberg, J. J.; Dapprich, S.; Daniels, A. D.; Farkas, O.; Foresman,
J. B.; Ortiz, J. V.; Cioslowski, J.; Fox, D. J. Gaussian 09; Gaussian, Inc.:
Wallingford, CT, 2010
(67) Iwaoka, M.; Komatsu, H.; Katsuda, T.; Tomoda, S. J. Am. Chem.
Soc. 2004, 126, 5309.
(68) Roy, D.; Sunoj, R. B. J. Phys. Chem. A 2006, 110, 5942.
(69) Sarma, B. K.; Mugesh, G. ChemPhysChem 2009, 10, 3013.
(70) Atoms in Molecules: A quantum Theory; Bader, R. F. W., Ed.;
Oxford University Press: New York, 1990.
(71) Iwaoka, M.; Tomoda, S. J. Org. Chem. 1995, 60, 5299.
(72) Behera, R. N.; Panda, A. RSC Adv. 2012, 2, 6948.
(73) Roy, D.; Sunoj, R. B. J. Mol. Struct.: THEOCHEM 2007, 809,
145.
(74) Schleyer, P. v. R.; Maerker, C.; Dransfeld, A.; Jiao, H.; Hommes,
N. J. R. v. E. J. Am. Chem. Soc. 1996, 118, 6317.
M
DOI: 10.1021/acs.joc.6b00173
J. Org. Chem. XXXX, XXX, XXX−XXX