Preparation and rearrangement study of novel thiophenium-and selenophenium-ylides

Article abstract of DOI:10.1135/cccc2009001

A series of the title ylides was prepared by reaction of fused thiophene and selenophene derivatives with di-tert-butyl diazomalonate. Their thermal stability depended highly on their structure. While the terminal thiophenium-and selenophenium-ylides smoo

Full text of DOI:10.1135/cccc2009001

Novel Thiophenium- and Selenophenium-Ylides
785
PREPARATION AND REARRANGEMENT STUDY OF
NOVEL THIOPHENIUM- AND SELENOPHENIUM-YLIDES
b
Aleš MACHARAa1, Václav KOZMÍKa2, Michaela POJAROVÁ ,
c
a3,
Hana DVOŘÁKOVÁ and Jiří SVOBODA
*
a
Department of Organic Chemistry, Institute of Chemical Technology, Prague,
Technická 5, CZ-166 28 Prague 6, Czech Republic; e-mail: ales.machara@vscht.cz,
vaclav.kozmik@vscht.cz, jiri.svoboda@vscht.cz
Department of Solid State Chemistry, Institute of Chemical Technology, Prague,
Technická 5, CZ-166 28 Prague 6, Czech Republic; e-mail: michaela.pojarova@vscht.cz
Central Laboratories, Institute of Chemical Technology, Prague,
1
2
3
b
c
Technická 5, CZ-166 28 Prague 6, Czech Republic; e-mail: hana.dvorakova@vscht.cz
Received Jan uary 23, 2009
Accepted March 7, 2009
Publish ed on lin e April 21, 2009
Dedicated to Dr. Alfred Bader on the occasion of his 85th birthday.
A series of th e title ylides was prepared by reaction of fused th ioph en e an d selen oph en e de-
rivatives with di-tert-butyl diazom alon ate. Th eir th erm al stability depen ded h igh ly on th eir
structure. Wh ile th e term in al th ioph en ium - an d selen oph en ium -ylides sm ooth ly rearran ged
to th e correspon din g th iopyran an d selen opyran derivatives, th e in tern al th ioph en e ylides
sh owed rem arkable stability. Th e latter also exh ibited h in dered rotation aroun d th e S–C
ylide bon d an d a h igh rotation al barrier could be establish ed in an NMR study.
Keyw ord s: Heterocycles; Th ioph en e; Selen oph en e; Th iopyran ; Selen opyran ; Ylides; Rear-
ran gem en t; Rin g expan sion .
A couple years ago1–3 we studied [4π + 2π] cycloaddition reaction s of fused
vin ylfuran s an d vin ylth ioph en es in order to syn th esize h igh er-fused
h eterocycles utilizable in design of n ovel liquid crystals4–6 an d con ductive
organ ic m aterials7–9. Wh en studyin g cycloaddition reaction s of fused
2-vin ylth ioph en es with dim eth yl acetylen edicarboxylate2 we foun d th at
th e cycloaddition afforded, besides th e expected products of a [4+2] reac-
tion , com poun ds possessin g th e fused cyclopen ta[b]th iopyran (th ialen e)
skeleton . A n on con certed m ech an ism of such un preceden ted th ioph en e-
to-th iopyran rin g expan sion was suggested in volvin g participation of th io-
ph en e sulfur atom an d form ation of a th iiran ium ion in th e course of th e
Collect. Czech. Chem. Commun. 2009, Vol. 74, No. 5, pp. 785–798
© 2009 Institute of Organic Chemistry and Biochemistry
doi:10.1135/cccc2009001

786
Machara, Kozmík, Pojarová, Dvořáková, Svoboda:
cycloaddition reaction . Th e abun dan ce of th e th iopyran s in th e product
m ixture depen ded on th e type of th e arom atic rin g fused to th e th ioph en e
rin g an d in creased from ben zen e th rough th ioph en e, ben zoth ioph en e to
ben zofuran m oiety. Form ation of such a structurally related th iiran ium spe-
cies was also con sidered in various th iopyran -th ioph en e rin g con trac-
tion s10–14 an d in th e Steven s rearran gem en t of th ioph en ium -ylides, th e
on ly kn own 15–18 th ioph en e-to-th iopyran rin g expan sion un til n ow. It was
also reported th at th e scope of th e rearran gem en t was lim ited to sim ple
th ioph en ium - an d selen oph en ium -ylides19, wh ile ben zoth ioph en ium -
ylides16 did n ot rearran ge to th e correspon din g ben zoth iopyran an alogues.
Th ese results in spired us to perform a study of syn th esis an d reactivity of a
series of n ovel th ioph en ium - or selen oph en ium -ylides, based on electron -
rich fused th ioph en es an d selen oph en es. We also dealt with som e of th e
h eterocycles earlier2.
RESULTS AND DISCUSSION
A series of m odel h eterocycles was ch osen – bicyclic ben zo[b]th ioph en e (1)
an d th ien o[3,2-b]th ioph en e (2), tricyclic th ien o[3,2-b][1]ben zoth ioph en e (3),
selen olo[3,2-b][1]ben zoth ioph en e (4), th ien o[3,2-b][1]ben zofuran (5) an d
selen olo[3,2-b][1]ben zofuran (6), an d fin ally tetracyclic [1]ben zoth ien o-
[3,2-b][1]ben zoth ioph en e (7).
Wh ile h eterocycles 3 an d 4 possess two com petitive n ucleoph ilic ch alco-
gen atom s (S, Se) in th e in tern al an d term in al rin gs, in th e fused derivatives
1, 2, 5, 6, th e ch alcogen oph en e rin g is term in al. In h eterocycle 7, both of
th e th ioph en e rin gs are in tern al.
Th e startin g h eterocycles 2–7 were obtain ed by th e publish ed proce-
dures7,20–22. Because of th e in con ven ien t syn th etic accesss23,24 an d lack of
in form ation 25 on th e selen oph en e-derived h eterocycles 4 an d 6, we elabo-
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Novel Thiophenium- and Selenophenium-Ylides
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rated an im proved on e-pot syn th esis, wh ich excluded h an dlin g th e h azard-
ous in term ediate selen ides (Sch em e 1). In th e first m eth od we used th e
fresh ly prepared sodium h ydrogen selen ide26 wh ich reacted with m eth yl
ch loroacetate an d subsequen tly with 3-ch loroben zo[b]th ioph en e-2-carb-
aldeh yde (8). Th e in term ediate form yl ester 10 was im m ediately cyclized
with sodium m eth oxide to ester 11a in 32% yield. We foun d th at a better
on e-pot m eth od of th e syn th esis of h eterocycle 4 was th e n ucleoph ilic aro-
m atic substitution of ch lorin e atom in ch loroaldeh yde 8 with th e in situ
prepared sodium selen ide an d subsequen t alkylation of th e in term ediate 12
with ch loroacetate ester followed by a base-catalyzed cyclization . In th e
stron gly basic m edium , partial tran sesterification of th e in itially form ed
m eth yl ester 11a was observed an d fin ally a m ixture of m eth yl 11a an d
eth yl ester 11b was obtain ed in th e ratio ca. 2.5:1 in overall 90% yield.
Due to fast decom position of NaBH4 in m eth an ol it was n ot possible to re-
place eth an ol by m eth an ol as solven t in th e effective preparation of th e
h ydrogen selen ide an ion 27 to avoid th e tran sterification reaction . Th e m ix-
ture of esters 11a/11b was th en h ydrolyzed to acid 13, th e decarboxylation
of wh ich with copper bron ze23 in quin olin e gave rise to h eterocycle 4. In
th e sam e way, th e h eterocycle 6 was obtain ed startin g with 3-ch loroben zo-
[b]furan -2-carbaldeh yde (9).
SCHEME 1
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Machara, Kozmík, Pojarová, Dvořáková, Svoboda:
Th e ylides were form ed by a rh odium acetate catalyzed reaction of
h eterocycles 1–7 with an excess of di-tert-butyl diazom alon ate (15), a rela-
tively stable28 diazocarbon yl. With th e exception of th e ben zofuran -fused
ch alcogen oph en es 5 an d 6, h eterocycles 1–4, 7 sm ooth ly afforded th e cor-
respon din g stable ylides 16, 17, 20–22 (Sch em e 2). Alth ough th e reaction
was carried out at room tem perature, ylides 18 an d 19 could n ot be iso-
lated, an d obviously due to th eir low stability, on ly products of th eir suc-
cessive rearran gem en t were obtain ed (vide in fra). In n o case, th e form ation
of bis-ylides due to double alkylation of both th e ch alcogen atom s in 2–4, 7
was observed. In addition , regardless of th e type of ch alcogen atom in 3
an d 4, alkylation proceeded regioselectively on th e in tern al th ioph en e rin g.
In th e reaction of 1, 2, an d 5, th e m ajor ylides were also accom pan ied by
a sm all am oun t of products of th eir successive cyclopropan ation 23–25.
Isolation of th e cyclopropan o derivative 25 in directly proves form ation of
th e correspon din g but n ot isolable ylide 18. Form ation of a structurally
related cyclopropan o com poun d was already observed in th e reaction of
2-tert-butylth ioph en e29,30
.
SCHEME 2
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Novel Thiophenium- and Selenophenium-Ylides
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Wh en studyin g th e th erm al rearran gem en ts of ylides 16–22, we h ave dis-
covered sign ifican t differen ces in th eir reactivity. First we foun d th at th e
th erm al stability16 of ben zoth ioph en ium -ylide 16 was lim ited to h eatin g in
a toluen e solution , wh ile in xylen e a slow rearran gem en t proceeds to th e
correspon din g ben zoth iopyran 26 alon g with dealkylation to ben zoth io-
ph en e (Sch em e 3). Ylides 20–22 sh owed an alogous stability; on ly slow de-
alkylation to th e paren t h eterocycles 3, 4, an d 7 was observed to th e exten t
of ca. 25%. Such dealkylation s leadin g to form ation of th e paren t h etero-
cycle an d th e correspon din g carben e in term ediate h ave already been de-
scribed31,32 an d also utilized in cyclopropan ation reaction s.
SCHEME 3
In con trast to th ese stable ylides, th e th ien oth ioph en e-derived ylide 17
rearran ged sm ooth ly on h eatin g in toluen e to th ien oth iopyran derivative
27 (55% yield). Th e h igh est reactivity was sh own by ben zofuran -fused
ylides 18 an d 19 wh ich were form ed by reaction of h eterocycles 5 an d 6
with diazom alon ate 15 but im m ediately rearran ged at room tem perature to
th iopyran 28 an d selen opyran 29 derivatives.
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Machara, Kozmík, Pojarová, Dvořáková, Svoboda:
Th e observed results are in good agreem en t with th e postulated m ech a-
n ism of th e Steven s rearran gem en t of th ioph en ium -ylides15. Stability of
ylides 16, 20–22 can be explain ed by en ergetically disadvan tgeous loss of
ben zen e or th ioph en e (selen oph en e) arom aticity in th e first step of th e re-
arran gem en t, wh ich eviden tly stron gly disfavours th e wh ole process. On
th e oth er h an d, in ylides 17–19, th e presen ce of electron -rich fused th io-
ph en e an d in particular furan rin gs stabilizes th e form ed th iiran ium or
selen iran ium species an d facilitates th e th ioph en e an d selen oph en e rear-
ran gem en t. Th ese results are in agreem en t with th ose obtain ed earlier
wh ere th e electron -rich h eterocycles fused to th e th ioph en e rin g stron gly
supported an alogous th ioph en e-th iopyran rearran gem en t in th e course of
a cycloaddition reaction 2.
1
Structures of all products were unam biguously assigned by H and 13C NMR
spectra an d stan dard NMR experim en ts. In th e ylides 16–22, a ch aracteristic
sh ift of th e ester carbon yl absorption in th e IR spectrum to 1704–1707 cm –1
was observed, wh ich in dicates th e presen ce of an electron -rich cen tre
boun d to th e α-position to th e carbon yl group an d th us form ation of an
S,C- or Se,C-ylide. Th e structure of ylide 21 was also proved by X-ray an aly-
sis of a sin gle crystal (Fig. 1), wh ich also revealed th at th e ylide is pyram idal
an d th e an gle between th e plan e of th e rin g an d th e ylide-carbon atom is
56°. Th is value is h igh er th an th at in sim ple th ioph en ium -ylides (50°)15,
but lower th an in th e correspon din g sulfon ium salts an d sulfoxides. On e of
th e tert-butyl ester group of th e m alon ate groupin g is located above th e rin g
an d th e oth er is away from th e rin g. Such structural features leadin g to th e
FIG. 1
View of th e X-ray crystal structure of ylide 21
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Novel Thiophenium- and Selenophenium-Ylides
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stereoisom erism resultin g from th e restricted rotation about th e ylidic S–C
bon d were also described in substitued th ioph en e an d ben zoth ioph en e
ylides15,16
.
1
In th e H an d 13C NMR spectra of 17, on ly on e sh arp sin glet of th e tert-
butyl groups an d a sin gle sign al of carbon yl carbon s appeared, wh ich in di-
cates th at th e rotation aroun d th e S–C bon d is n ot substan tially h in dered,
at least on th e NMR tim escale. On th e oth er h an d, spectral properties of
1
ylides 20–22 were differen t. In th eir H NMR spectra m easured in deuterio-
ch loroform on a 500 MHz in strum en t, th ey exh ibited an extrem ely broad
sign al of th e tert-butyl proton s an d two distin ct sign als of th e carbon yl car-
bon s appeared in th eir 13C NMR spectra. Wh en replacin g deuterioch loro-
form with deuterated 1,1,2,2-tetrach loroeth an e, two broad sin glets of tert-
butyl groups appeared in all th e ylides 20–22 at 25 °C wh ich proved th e
n on equivalen ce of both ester groups. Coalescen ce of th e sign als of th e tert-
butyl groups in 20 was ach ieved at 313 K, wh ile in 21 at 303 K an d in 22
at 373 K, wh ich correspon ds to a rotation al barrier of ∆G = 59, 57 an d 70.5
kJ m ol–1, respectively.
It sh ould be con cluded th at th ioph en ium -ylides can also be effectively
prepared by a reaction of fused th ioph en e h eterocycles with diazom alon ate
ester 15. No com petitive alkylation reaction was observed in h eterocycles 3
an d 4; on ly alkylation on th e in tern al th ioph en e rin g proceeded. Un like33
on ly m on oylides were form ed with th ien oth ioph en es an d selen oth ioph en e
2–4. Ylides 20–22 exh ibited h igh th erm al stability an d did n ot rearran ge to
th iopyran derivatives obviously due to a h igh en ergy barrier associated with
th e loss of arom aticity of th e fused n eigh bourin g ben zen e or th ioph en e
(selen oph en e) in th e in itial step of th e rearran gem en t process. Ylides 17–19
derived from th e electron -rich h eterocycles 2, 5, 6 sm ooth ly rearran ge to
n ew fused th iopyran s 27–29. Alth ough it was postulated15,34 th at th io-
pyran s are th e kin etic products of th e rearran gem en t, n eith er of th e pre-
pared th iopyran s 26–29 rearran ged on lon g-term h eatin g in toluen e to th e
correspon din g 2-(th ioph en -2-yl)m alon ates.
EXPERIMENTAL
Meltin g poin ts were determ in ed on a Leica VM TG block an d are un corrected. Elem en tal
an alyses were carried out on a Perkin –Elm er 2400 in strum en t. IR spectra (ν, cm –1) were re-
corded on a Nicolet 740 FTIR spectrom eter in ch loroform . NMR spectra (δ, ppm ; J, Hz) were
m easured on a Varian Gem in i 300 HC (300 MHz for 1H an d 75 MHz for 13C) an d Bruker
500. Deuterioch loroform was used as solven t an d th e sign als of th e solven t served as in ter-
n al stan dards. Th e 2D experim en ts, COSY, HMBC, HMQC, were carried out usin g pulse se-
quen ce an d program m e provided by th e m an ufacturer.
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Machara, Kozmík, Pojarová, Dvořáková, Svoboda:
X-ray data for 21: C21H24O4SSe·CHCl3, M = 570.80 g m ol–1, m on oclin ic system , space
group P21/n, a = 11.428(2) Å, b = 11.193(2) Å, c = 19.649 (3) Å, β = 92.33 (1)°, Z = 4, V =
2511.2 (6) Å3, Dc = 1.510 g cm –3, µ(CuKα) = 5.957 m m –1, crystal dim en sion s of 0.06 × 0.22 ×
0.37 m m . Data were collected at 150(2) K on a Xcalibur PX diffractom eter with graph ite
m on och rom atized CuKα radiation . Th e structure was solved by direct m eth ods35 usin g
th e SHELX suite of program s36, an d an isotropically refin ed by full-m atrix least-squares on F2
values to fin al R = 0.0877 an d Rw = 0.2502 usin g 5175 in depen den t reflection s (θm ax
=
76.62°) an d 320 param eters. Th e position s of disordered groups were foun d from th e elec-
tron den sity m aps. Disordered fragm en ts were th en placed in appropriate position s, an d all
distan ces between n eigh bourin g atom s an d an gles were fixed. Because of lower quality of
m easured crystal, th e disorder atom s of five-m em bered rin g with Se were refin ed on ly
isotropically an d th e residual den sity th an ks to th e presen ce of sulfur an d selen ium atom s is
1.27 e Å–3. At th e en d of refin em en t, site occupan cies were fixed an d h ydrogen atom s were
placed in calculated position s.
CCDC 694269 con tain s th e supplem en tary crystallograph ic data for th is paper. Th ese data
can be obtain ed free of ch arge via www.ccdc.cam .ac.uk/con ts/retrievin g.h tm l (or from th e
Cam bridge Crystallograph ic Data Cen tre, 12, Un ion Road, Cam bridge, CB2 1EZ, UK; fax:
+44 1223 336033; or deposit@ccdc.cam .ac.uk).
Caution! Many inorganic and organic selenium compounds are highly toxic. All operations
should be conducted in an efficient hood. Gloves and appropriate protective clothes should be worn
while performing these experiments.
Meth yl (11a) an d Eth yl Selen olo[3,2-b][1]ben zoth ioph en e-2-carboxylate (11b)
Method A. To a slurry of grey selen ium (1.6 g, 20.3 m m ol) in eth an ol (30 m l), NaBH4
(1.54 g, 40.7 m m ol) was added portion wise at 0 °C in argon atm osph ere, an d th e m ixture
was stirred un til NaBH4 an d th e coloration diasappeared (n o evolution of h ydrogen ap-
peared wh en a sam ple of th e reaction m ixture was acidified with 5% aqueous h ydroch loric
acid). Meth yl ch loroacetate (2.2 g, 20.3 m m ol, 1.8 m l) was added an d th e m ixture stirred at
0 °C for 2 h . Th en a solution of sodium m eth oxide (0.55 g, 10.2 m m ol) in m eth an ol (40 m l)
7
was added dropwise followed by addition of ch loroaldeh yde 8 (1.0 g, 5.1 m m ol) an d
h eated to boilin g for 2 h . Th e m ixture was decom posed with water (50 m l) an d extracted
with eth yl acetate (3 × 30 m l). Th e com bin ed organ ic solution was wash ed with water
(30 m l), brin e (2 × 30 m l), an d dried with an h ydrous m agn esium sulfate. After evaporation ,
th e crude product was purified by colum n ch rom atograph y (silica gel, toluen e). 0.48 g (32%)
of 11a was obtain ed, m .p. 135–138 °C. For C12H8O2SSe (295.2) calculated: 48.82% C,
2.73% H; foun d: 49.05% C, 2.83% H. 1H NMR: 3.92 s, 3 H (OCH3); 7.39 m , 1 H; 7.42 m ,
1 H; 7.84 m , 2 H (H-5 an d H-8); 8.24 s, 1 H (H-3). 13C NMR: 52.5 (OCH3), 122.5 (CH), 123.7
(CH), 125.0 (CH), 125.9 (CH), 129.1 (CH), 134.7, 138.4, 138.6, 141.3, 143.0, 163.7 (C=O).
IR: 3012, 2957, 2929, 2855, 1705 (C=O), 1518, 1444, 1436, 1339, 1319, 1278, 1257, 1240,
1149, 1096, 1067, 964, 928.
Method B. To a slurry of grey selen ium (0.44 g, 5.6 m m ol) in eth an ol (30 m l), NaBH4
(0.28 g, 7.3 m m ol) was added portion wise at 0 °C in argon atm osph ere, an d th e m ixture
was stirred un til NaBH4 an d th e coloration disappeared. Th en sodium h ydride (0.22 g, 55%
7
in oil, 5 m m ol) was added. After stirrin g for 5 m in , a solution of ch loroaldeh yde 9 (1.0 g,
5.1 m m ol) in THF (5 m l) was added an d th e m ixture was stirred at room tem perature for
2 h . Th en m eth yl ch loroacetate (1.21 g, 11 m m ol) was added, th e m ixture was furth er
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Novel Thiophenium- and Selenophenium-Ylides
793
stirred for 1 h , an d fin ally sodium m eth oxide (0.55 g, 10.2 m m ol) was added in on e portion
an d th e m ixture was h eated to boilin g for 1 h . After coolin g to room tem perature, th e m ix-
ture was decom posed with water (20 m l) an d extracted with eth yl acetate (3 × 50 m l). Th e
com bin ed organ ic solution was wash ed with water (30 m l), brin e (2 × 30 m l), an d dried
with an h ydrous m agn esium sulfate. After evaporation , th e crude product was purified by
colum n ch rom atograph y (silica gel, toluen e). Yield 1.38 g (90%) of a m ixture of m eth yl 11a
an d eth yl ester 11b in th e ratio 2.5:1 was obtain ed. 1H NMR of 11b: 1.40 t, 3 H, J = 6.8
(CH3); 4.37 q, 2 H (OCH2); 7.34 m , 2 H (H-6 an d H-7); 7.75 m , 1 H; 7.79 m , 1 H; 8.19 s, 1 H
(H-3). 13C NMR: 14.2 (CH3), 61.4 (OCH2), 122.3 (CH), 123.6 (CH), 124.8 (CH), 125.6 (CH),
128.7 (CH), 134.6, 138.2, 139.2, 141.0, 142.9, 163.1 (C=O). IR: 2984, 2941, 2909, 1700
(C=O), 1518, 1469, 1444, 1413, 1369, 1338, 1319, 1274, 1256, 1240, 1149, 1064 m .
Selen olo[3,2-b][1]ben zoth ioph en e-2-carboxylic Acid (13)
A m ixture of esters 11a/11b (7.0 g), sodium h ydroxide (9.1 g, 0.22 m ol), water (60 m l) an d
m eth an ol (40 m l) was h eated to reflux un der stirrin g for 2 h . After coolin g to room tem pera-
ture it was acidified with 10% aqueous h ydroch loric acid (125 m l), th e solid was filtered off
an d wash ed with water. Crystallization from eth an ol afforded 5.73 g (90%) of acid 13, m .p.
269–270 °C (m .p.23 268 °C). 1H NMR (DMSO-d6): 7.40 m , 2 H; 7.79 s, 1 H (H-3); 7.91 dd,
1 H, J1 = 7.3, J2 = 1.7; 8.00 dd, 1 H, J1 = 7.9, J2 = 1.5.
Selen olo[3,2-b][1]ben zoth ioph en e (4)
A m ixture of acid 13 (5.0 g, 17.8 m m ol), copper bron ze (0.5 g, 7.9 m m ol) an d fresh ly dis-
tilled quin olin e (40 m l) was stirred at 160 °C for 1.5 h . Wh en CO2 evolution ceased, th e
m ixture was cooled to room tem perature an d filtered, th e filtrate was poured on a m ixture
of con cen trated h ydroch loric acid (40 m l) an d ice an d th en extracted with h exan e (3 ×
100 m l). Th e com bin ed h exan e layers were wash ed with water (50 m l), brin e (2 × 50 m l),
an d dried with an h ydrous m agn esium sulfate. After evaporation of th e solven t, th e residue
was purified by colum n ch rom atograph y (silica gel, h exan e) to afford 3.75 g (89%) of 4,
m .p. 114–115 °C (m .p.23 112 °C). 1H NMR (DMSO-d6): 7.35 dt, 1 H, J1 = 7.7, J2 = 1.4;
7.41 dt, 1 H, J1 = 7.6, J2 = 1.4; 7.55 d, 1 H, J(2,3) = 5.5 (H-3); 7.80 dd, 1 H; 7.87 dd, 1 H;
8.10 d, 1 H (H-2). 13C NMR: 121.6 (CH), 122.8 (CH), 123.7 (CH), 124.3 (CH), 124.6 (CH),
131.6 (C-2), 135.1, 135.4, 139.1, 142.0. IR: 3106, 3065, 3009, 2925, 2853, 1601, 1469, 1441,
1335, 1253, 1209, 1171, 1064.
Eth yl Selen olo[3,2-b][1]ben zofuran -2-carboxylate (12)
In th e sam e way as for esters 11, th e reaction of grey selen ium (1.86 g, 23.6 m m ol), NaBH4
22
(1.78 g, 47.2 m m ol), sodium h ydride (1.03 g, 55% in oil, 23.6 m m ol), ch loroaldeh yde 9
(3.87 g, 21.4 m m ol), eth yl ch loroacetate (5.77 g, 47.1 m m ol), an d sodium m eth oxide
(2.58 g, 47.1 m m ol) afforded after purification of th e crude product by colum n ch rom atog-
raph y (silica gel, toluen e) 2.43 g (40%) of eth yl ester 12, m .p. 95 °C (m eth an ol) (m .p.25 91 °C).
1H NMR: 1.41 t, 3 H, J = 7.0 (CH3); 4.39 q, 2 H (CH2); 7.33 dt, 1 H, J1 = 7.7, J2 = 1.2; 7.41 dt,
1 H, J1 = 7.3, J2 = 1.5; 7.59 ddd, 1 H, J1 = 7.3, J2 = 1.2, J3 = 0.5; 7.72 ddd, 1 H; 8.15 s, 1 H
(H-3). 13C NMR: 14.3 (CH3), 61.6 (OCH2), 112.5 (CH), 119.8 (CH), 120.4 (CH), 123.4 (CH),
125.5, 125.6, 126.2 (CH), 138.3, 158.2, 158.7, 163.4 (C=O). IR: 2984, 1698 (C=O), 1462,
1397, 1384, 1274, 1235, 1032.
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Selen olo[3,2-b][1]ben zofuran -2-carboxylic Acid (14)
Hydrolysis of 12 (2.4 g, 8.2 m m ol) was ach ieved as for 13. Crystallization from eth an ol
afforded 2.1 g (96%) of acid 14, m .p. 273–274 °C (m .p.25 272 °C). 1H NMR (DMSO-d6):
7.37 dt, 1 H, J1 = 7.7, J2 = 1.0; 7.45 dt, 1 H, J1 = 7.3, J2 = 1.4; 7.72 d, 1 H, J = 7.3; 8.04 dd,
1 H, J1 = 7.7, J2 = 1.4; 8.25 s, 1 H (H-3); 13.35 bs, 1 H (OH).
Selen olo[3,2-b][1]ben zofuran (6)
Decarboxylation of acid 12 (2.07 g, 7.8 m m ol) by m ean s of copper bron ze (1.2 g, 18.7 m m ol)
an d quin olin e (20 m l) at 160 °C afforded after colum n ch rom atograph y (silica gel, h exan e)
1.22 g (71%) of 6, m .p. 60 °C (m .p.25 57 °C). 1H NMR: 7.34 m , 2 H; 7.49 d, 1 H, J(2,3) = 5.7;
7.60 m , 1 H; 7.69 m , 1 H; 7.98 d, 1 H, J(2,3) = 5.7. 13C NMR: 112.2 (CH), 114.6 (CH), 118.7,
119.4 (CH), 122.9 (CH), 124.3 (CH), 126.1, 131.2 (CH), 158.2, 160.2.
Preparation of Ylides. Gen eral Procedure
A. A m ixture of ben zo[b]th ioph en e (1) (0.49 g, 3.65 m m ol), di-tert-butyl diazom alon ate (15)
(1.32 g, 5.47 m m ol), rh odium acetate (5 m g) an d 1,2-dich loroeth an e (5 m l) was stirred at
room tem perature for 16 h . After evaporation th e residue was separated by colum n ch rom a-
tograph y (silica gel, ch loroform + 5% m eth an ol) an d afforded 1.06 g (83%) of 16 an d 25 m g
(1%) of 23.
Di-tert-butyl 2-(1λ4-benzo[b]thiophen-1-ylidene)malonate (16), m .p. 164–165 °C. For
C
19H24O4S (348.5) calculated: 65.49% C, 6.94% H; foun d: 65.23% C, 7.01% H. 1H NMR:
1.43 s, 18 H (6 × CH3); 6.83 d, 1 H, J = 5.8; 7.38 d, 1 H, J = 5.8; 7.50 dt, 1 H, J1 = 7.3, J2
=
1.4; 7.56 dt, 1 H, J1 = 7.3, J2 = 1.3; 7.63 m , 1 H; 7.78 m , 1 H. 13C NMR: 28.2 (6 × CH3), 51.5,
78.7 (2 quatern ary C), 123.8 (CH), 125.4 (CH), 128.2 (CH), 128.9 (CH), 130.1 (CH), 133.3
(CH), 137.8, 137.9, 164.6 bs (2 × C=O). IR: 2980, 2931, 1705 (C=O), 1667, 1632, 1476, 1367,
1327, 1169, 1082, 1059, 1032.
Di-tert-butyl 2-[1,1-bis(tert-butyloxycarbonyl)-1a,6b-dihydro-2λ4-1H-benzo[b]cyclopropa[d]thio-
phen-2-ylidene]malonate (23). For C30H42O8S (562.7) calculated: 64.03% C, 7.52% H; foun d:
64.12% C, 7.65% H. 1H NMR: 1.07 s, 9 H; 1.37 s, 18 H; 1.50 s, 9 H; 3.72 d, 1 H, J = 6.7;
3.92 d, 1 H, J = 6.7; 7.40 m , 1 H; 7.49 m , 2 H; 7.60 m , 1 H. 13C NMR: 27.3 (3 × CH3), 27.9
(3 × CH3), 28.7 (6 × CH3), 39.9 (CH), 44.0, 49.2 (CH), 79.1 (2 quatern ary C), 82.6, 84.0,
125.5 (CH), 127.3 (CH), 129.2 (CH), 130.9 (CH), 136.8, 138.21, 164.7 (C=O), 165.1 (C=O),
165.3 (2 × C=O) (1 quatern ary C n ot detected). IR: 2978, 2931, 1724 (C=O), 1686, 1634,
1477, 1367, 1323, 1250, 1158, 1081, 1030.
B. An alogous reaction of rin g system 2 (0.82 g, 5.9 m m ol), diazom alon ate 15 (1.7 g,
7 m m ol) an d rh odium acetate (5 m g) in 1,2-dich loroeth an e (5 m l) after ch rom atograph ic
separation (silica gel, h exan e, toluen e, ch loroform + 10% m eth an ol) afforded 1.60 g (76%)
of ylide 17 an d 0.20 g (6%) of cyclopropan o derivative 24.
Di-tert-butyl 2-(1λ4-thieno[3,2-b]thiophen-1-ylidene)malonate (17), m .p. 134–135 °C. For
C
17H24O4S2 (354.5) calculated: 57.60% C, 6.26% H; foun d: 57.52% C, 6.36% H. 1H NMR:
1.28 s, 18 H; 6.82 dd, 1 H, J1 = 5.7, J2 = 1.6; 7.23 dd, 1 H, J1 = 5.2, J2 = 0.6; 7.33 dd, 1 H, J1
=
5.7, J2 = 0.6; 7.54 dd, 1 H, J1 = 5.2, J2 = 1.6. 13C NMR: 27.9 (6 × CH3), 50.4, 78.7 (2 quater-
n ary C), 120.3 (CH), 127.9 (CH), 131.1 (CH), 132.2 (CH), 137.8, 142.7, 164.2 (2 × C=O).
IR: 2 980, 2 930, 1706 (C=O), 1668, 1624, 1477, 1454, 1366, 1325, 1252, 1169, 1084, 1060.
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795
Di-tert-butyl 2-[1,1-bis(tert-butyloxycarbonyl)-2λ4-1H-1a,5b-dihydrocyclopropa[b]thieno[d]thio-
phen-2-ylidene]malonate (24), m .p. 166–167 °C. For C28H40O8S2 (568.8) calculated: 59.13% C,
7.09% H; foun d: 58.86% C, 7.19% H. 1H NMR: 1.10 s, 9 H; 1.31 s, 18 H; 1.40 s, 9 H; 3.72 d,
1 H, J = 6.7; 3.93 d, 1 H, J = 6.7; 6.81 d, 1 H, J = 5.3; 7.25 d, 1 H, J = 5.3. 13C NMR: 27.2
(3 × CH3), 27.7 (3 × CH3), 28.6 (6 × CH3), 34.51 (CH), 44.8, 57.4 (CH), 62.9, 78.9 (2 quater-
n ary C), 82.8, 84.1, 120.5 (CH), 131.8 (CH), 134.1, 143.7, 161.1 (C=O), 164.5 (C=O), 165.1
(2 × C=O). IR: 2982, 2932, 1722 (C=O), 1667, 1628, 1477, 1455, 1370, 1324, 1158, 1082,
1055, 1031.
C. Startin g with rin g system 3 (0.30 g, 1.6 m m ol) an d diazom alon ate 15 (0.76 g, 3.2 m m ol),
after colum n ch rom atograph y (silica gel, ch loroform + 10% m eth an ol) 0.62 g (97%) of
di-tert-butyl 2-(4λ4-thieno[3,2-b][1]benzothiophen-4-ylidene)malonate (20) was obtain ed, m .p.
171–173 °C. For C21H24O4S2 (404.6) calculated: 62.35% C, 5.98% H; foun d: 62.15% C, 6.11% H.
1H NMR: 1.22 bs, 18 H; 7.30 d, 1 H, J(2,3) = 5.2; 7.45 m , 1 H; 7.53 d, 1 H, J(2,3) = 5.2;
7.58 m , 1 H; 7.67 d, 1 H, J = 7.6; 7.77 d, 1 H, J = 7.9. 13C NMR: 28.5 (6 × CH3), 54.0, 78.6,
121.2 (CH), 121.6 (CH), 124.8 (CH), 127.5 (CH), 130.1 (CH), 130.6 (CH), 133.3, 136.3,
142.1, 142.5, 166.8 (C=O), 171.3 (C=O). IR: 2996, 2976, 2931, 1728 (C=O), 1705 (C=O),
1667, 1633, 1476, 1454, 1390, 1366, 1327, 1167, 1084, 1059.
D. In the same way, ring system 4 (0.50 g, 2.1 mmol) and diazomalonate 15 (1.02 g, 4.2 mmol)
afforded after purification by colum n ch rom atograph y (silica gel, ch loroform + 10% m eth an ol)
0.92 g (97%) of di-tert-butyl 2-(4λ4-selenolo[3,2-b][1]benzothiophen-4-ylidene)malonate (21),
m .p. 184–187 °C. For C21H24O4SSe (451.5) calculated: 55.87% C, 5.36% H; foun d: 55.71% C,
5.44% H. 1H NMR: 1.19 bs, 18 H; 7.44 m , 1 H; 7.49 d, 1 H, J(2,3) = 5.6 (H-3); 7.59 m , 2 H;
7.76 d, 1 H, J = 7.8; 8.17 d, 1 H (H-2). 13C NMR: 28.3 (6 × CH3), 54.3, 78.8, 122.6 (CH),
123.2 (CH), 124.8 (CH), 127.7 (CH), 130.8 (CH), 135.0 (CH), 135.8, 138.3, 141.3, 145.7,
165.0 (broad). IR: 2978, 2928, 1704 (C=O), 1666, 1633, 1476, 1366, 1327, 1083, 1059, 1032.
E. By th e sam e procedure, rin g system 7 (0.4 g, 1.66 m m ol) an d diazom alon ate 15 (0.6 g,
2.50 m m ol) afforded after colum n ch rom atograph y (silica gel, ch loroform an d th en ch loro-
form + 10% m eth an ol) 0.74 g (97%) of di-tert-butyl 2-(5λ4-benzothieno[3,2-b][1]benzothio-
phen-4-ylidene)malonate (22), m .p. 105–107 °C. For C25H26O4S2 (454.6) calculated: 66.05% C,
5.76% H; foun d: 66.07% C, 5.72% H. 1H NMR: 0.76 s, 9 H; 1.65 s, 9 H; 7.48 m , 2 H; 7.54 m ,
1 H; 7.63 dt, 1 H, J1 = 7.4, J2 = 1.1; 7.73 m , 1 H; 7.84 m , 1 H; 7.93 m , 2 H. 13C NMR: 27.74
(3 × CH3), 28.76 (3 × CH3), 53.40, 78.12, 79.40, 121.57 (CH), 122.56 (CH), 123.86 (CH),
124.82 (CH), 125.98 (CH), 126.04 (CH), 128.28 (CH), 130.15, 130.77 (CH), 131.81, 133.73,
142.06 (2 quatern ary C), 142.71, 162.43 (C=O), 166.45 (C=O). IR: 2980, 1707 (C=O), 1667,
1632, 1367, 1328, 1169, 1084, 1059.
Reaction of Rin g System 5 with Diazom alon ate 15
A m ixture of com poun d 5 (0.39 g, 2.24 m ol), diazom alon ate 15 (0.81 g, 3.4 m m ol) an d rh o-
dium acetate (5 m g) in 1,2-dich loroeth an e (5 m l) was stirred at room tem perature for 16 h .
Th e crude product after evaporation was separated by colum n ch rom atograph y (silica gel,
ch loroform , ch loroform + 10% m eth an ol). An am oun t of 0.14 g of th e startin g com poun d 5
was recovered, followed by 0.48 g (55%) of 28 an d 0.06 g (5%) of 25.
Di-tert-butyl 2H-thiopyrano[3,2-b][1]benzofuran-2,2-dicarboxylate (28), m .p. 121–122 °C. For
C
21H24O5S (388.5) calculated: 64.93% C, 6.23% H; foun d: 64.74% C, 6.15% H. 1H NMR:
1.47 s, 18 H; 5.99 d, 1 H, J(3,4) = 10.5 (H-3); 6.68 d, 1 H, J(3,4) = 10.5 (H-4); 7.24 m , 2 H;
7.40 dd, 1 H, J1 = 7.4, J2 = 1.7; 7.46 dd, 1 H, J1 = 7.3, J2 = 1.7. 13C NMR: 27.5 (6 × CH3),
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796
Machara, Kozmík, Pojarová, Dvořáková, Svoboda:
60.4, 83.5, 106.5, 111.4 (CH), 119.2 (CH), 119.3 (CH), 119.4 (CH), 123.0 (CH), 125.2 (CH),
125.9, 147.6, 154.3, 165.7 (C=O). IR: 2979, 2934, 1736 (C=O), 1450, 1369, 1255, 1148, 1065.
Di-tert-butyl 2-[1,1-bis(tert-butyloxycarbonyl)-2λ4-1H-1a,7b-dihydrocyclopropa[4,5]thieno[3,2-b]-
[1]-benzofuran-2-ylidene]malonate (25). For C32H42O9S (602.8) calculated: 63.77% C, 7.02% H;
foun d: 63.72% C, 7.25% H. 1H NMR: 1.06 s, 9 H; 1.41 s, 18 H; 1.49 s, 9 H; 3.73 d, 1 H, J =
6.5; 4.10 d, 1 H, J = 6.5; 7.27 dt, 1 H, J1 = 7.6, J2 = 1.2; 7.34 dt, 1 H, J1 = 7.6, J2 = 1.5;
7.44 dd, 1 H, J1 = 7.6, J2 = 1.2; 7.52 dd, 1 H, J1 = 7.6, J2 = 1.5. 13C NMR: 27.2 (3 × CH3), 27.8
(3 × CH3), 28.7 (6 × CH3), 29.9 (CH2), 45.4, 56.0 (CH2), 61.5, 79.2, 83.2, 84.6, 112.6 (CH),
112.7, 119.5 (CH), 121.8, 124.5 (CH), 125.7 (CH), 160.3, 161.2, 161.4, 164.1, 165.2 (1 qua-
tern ary C n ot detected). IR: 2979, 2932, 1726 (C=O), 1693, 1628, 1477, 1368, 1307, 1250,
1158, 1090, 1030.
In th e sam e way, th e selen oph en e derivative 6 (1.0 g, 4.52 m m ol) afforded 0.21 g (11%)
of di-tert-butyl 2H-selenopyrano[3,2-b][1]benzofuran-2,2-dicarboxylate (29). For C21H24O5Se
(435.4) calculated: 57.93% C, 5.56% H; foun d: 57.99% C, 5.58% H. 1H NMR: 1.44 s, 18 H;
5.80 d, 1 H, J(3,4) = 11.0; 6.56 d, 1 H, J(3,4) = 11.0; 7.17 m , 2 H; 7.32 m , 2 H. 13C NMR:
27.61 (6 × CH3), 55.59 (C-2), 83.56, 111.52 (CH), 120.03 (CH), 123.02 (CH), 125.10 (CH),
127.47, 128.9 (CH), 128.99 (CH), 147.86, 154.33, 166.25 (1 quatern ary C n ot detected).
IR: 2982, 2933, 1724 (C=O), 1522, 1370, 1162, 1023.
Di-tert-butyl 2H-ben zo[b]th iopyran -2,2-dicarboxylate (26)
A solution of ylide 16 (0.63 g, 1.80 m m ol) in dry xylen e (10 m l) was h eated to boilin g for
2.5 h , th e solven t was evaporated an d th e residue purified by colum n ch rom atograph y (silica
gel, h exan e/eth yl acetate 6:1). An am oun t of 0.15 g (62%) of th e paren t h eterocycle 1 was
recovered followed by 13 m g (21%) of 26, m .p. 173–175 °C. For C19H24O4S (348.5) calcu-
lated: 65.49% C, 6.94% H; foun d: 65.27% C, 7.11% H. 1H NMR: 1.43 s, 18 H; 6.09 d, 1 H,
J(3,4) = 10.2; 6.63 d, 1 H, J(3,4) = 10.2; 7.08 m , 3 H; 7.22 m , 1 H. 13C NMR: 27.14 (6 × CH3),
58.9, 83.1 (2 quatern ary C), 120.9 (CH), 125.7 (CH), 126.0 (CH), 128.5 (2 × CH), 129.2,
129.6, 129.8 (CH), 166.1 (2 × C=O). IR: 2982, 2935, 1731 (C=O), 1474, 1371, 1279, 1255,
1162, 1145, 1075, 1018.
Di-tert-butyl 2H-Th ien o[3,2-b]th iopyran -2,2-dicarboxylate (27)
A solution of 17 (1.14 g, 3.2 m m ol) in dry toluen e (20 m l) was h eated to boilin g for 50 m in .
Th e solven t was evaporated an d th e residue purified by colum n ch rom atograph y (silica gel,
h exan e/eth yl acetate 4:1). 0.05 g (11%) of h eterocycle 2 an d 0.73 g (64%) of 27 were
isolated, m .p. 67–69 °C. For C17H22O4S2 (354.5) calculated: 57.60% C, 6.26% H; foun d:
57.47% C, 6.41% H. 1H NMR: 1.43 s, 18 H; 5.86 d, 1 H, J(3,4) = 10.3 (H-3); 6.62 dd, 1 H, J1
=
10.3, J = 0.6 (H-4); 6.84 dd, 1 H, J1 = 5.2, J2 = 0.6 (H-7); 7.18 d, 1 H, J = 5.2 (H-6). 13C NMR:
27.4 (6 × CH3), 59.9, 82.9 (2 quatern ary C), 116.1 (CH), 122.6 (CH), 124.5 (CH), 124.6,
125.1 (CH), 128.4, 165.8 (2 × C=O). IR: 2982, 1731 (C=O), 1477, 1395, 1371, 1278, 1259,
1159, 1143, 1083.
Th erm al Stability of Ylides 20–22
Ylide 20 (202 m g, 1 m m ol) in dry toluen e (10 m m ol) was h eated to boilin g for 20 h . Th e
solven t was evaporated an d th e residue separated by colum n ch rom atograph y (silica gel, elu-
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Novel Thiophenium- and Selenophenium-Ylides
797
tion with ch loroform an d th en with ch loroform + 10% m eth an ol). Con poun d 3 (24 m g,
25%) an d un reacted ylide 20 (133 m g, 66%) were isolated.
In th e sam e way reaction of ylide 21 (187 m g, 0.41 m m ol) afforded 22 m g (23%) of 4 an d
112 m g (60%) of 21. An alogously, reaction of ylide 22 (129 m g, 0.283 m m ol) afforded 16 m g
(23%) of 7 alon g with 91 m g (71%) of un reacted 22.
This work was supported by the Ministry of Education, Youth and Sports of the Czech Republic
(project OC176).
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