Protecting Groups for Organoselenium Compounds

Full text of DOI:10.1021/jo972144a

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J . Org. Chem. 1998, 63, 2397-2400
2397
Sch em e 1
P r otectin g Gr ou p s for Or ga n oselen iu m
Com p ou n d s
William A. Reinerth and J ames M. Tour*
Department of Chemistry and Biochemistry, University of
South Carolina, Columbia, South Carolina 29208
Received November 24, 1997
In tr od u ction
In the course of our investigations on self-assembled
monolayers (SAMs) of organoselenium compounds on
gold,1 we desired a protecting group for selenium that
was stable to a variety of reaction conditions yet was
easily removed under the conditions used for monolayer
formation. We have previously reported a method for the
in situ deprotection of aryl thioacetates using NH4OH.2
The thiols that were generated in situ served as molec-
ular scale “alligator clips” (wire-to-surface binding units)
for adhesion of molecular wires to metallic probes. With
a desire to change the nature of the alligator clip to a
more metallic element, and taking a lead from our sulfur
chemistry, we decided to investigate the use of seleno-
carbamates, selenocarbonates, and selenoacetates as end
groups for the molecular wires. We have also examined
their deprotection and their stability with respect to Pd/
Cu-catalyzed coupling reactions.
Utilization of organoselenium compounds often re-
quires use of a protected selenol since, under ambient
conditions, selenols readily oxidize to diselenides.3 Se-
lenols are usually protected as the symmetrical diselenide
(RSeSeR) or as the selenocyanate (RSeCN); however,
there are serious drawbacks and limitations to these
approaches. For example, diselenides require strongly
reducing conditions, such as Na/NH3 or NaBH4, to cleave
the Se-Se bond. Additionally, the diselenide approach
is incompatible for use with R,ω-diselenols since the
protected material would consist of insoluble poly(di-
selenides), and diselenides are likely not stable toward
Pd-catalyzed cross-coupling conditions as the Se-Se bond
will oxidatively add to the Pd(0) catalyst and interrupt
the catalytic cycle.4 While selenocyanates can be depro-
tected under various conditions, their syntheses usually
require the use of potassium selenocyanate (KSeCN) or
selenocyanogen [(SeCN)2] and their deprotection often
releases HCN.5 Although potassium selenocyanate is
strongly nucleophilic and readily reacts with alkyl halides
and aryldiazonium salts to form alkyl and aryl seleno-
cyanates,6 KSeCN requires an unappealing preparation
(stirring a molten mixture of KCN and elemental Se)7
and is extremely hygroscopic, decomposing slowly on
contact with the common laboratory atmosphere. Sele-
nocyanogen is prepared from KSeCN at low temperatures
and is extremely toxic. All three of the protecting groups
described here offer significant advantages over disele-
nides and selenocyanates.
Ever since Sharpless and Lauer converted epoxides to
allylic alcohols using diphenyl diselenide,8 the use of
selenium compounds in organic synthesis has been an
area of intense study.9 In recent years, a number of
researchers have employed selenocarbamates, selenocar-
bonates, and selenoacetates as efficient sources of acyl
radicals.10 Among other applications, they have been
used in ring-closing reactions to form lactones10c and
substituted tetrahydrofurans,10d for the radical deoxy-
genation of alcohols,11 and for the conversion of carbox-
ylic acids to isonitriles.10e The many examples of the
homolytic cleavage of the acyl C-Se bond to give the
corresponding selenyl radical are contrasted by a surpris-
ing paucity of examples of selenolate anions derived from
selenoacyl compounds. Vinyl selenoacetates have been
cleaved by Na/HMPA in DMF to give vinyl selenolates
that were oxidized with iodine to yield divinyl dis-
elenides.12 Also, aryl selenoesters have been deprotected
(5) Organic Selenium Compounds: Their Chemistry and Biology;
Klayman, D. L., Gu¨nther, W. H. H., Eds.; The Chemistry of Organo-
metallic Compounds; J ohn Wiley & Sons: New York, 1973; pp 42-44.
(6) The Chemistry of Organic Selenium and Tellurium Compounds;
Patai, S., Ed.; The Chemistry of Functional Groups; J ohn Wiley &
Sons: New York, 1987; Vol. 2, pp 541-574.
(7) Waitkins, G. R.; Shutt, R. Inorg. Synth. 1946, 2, 186.
(8) Sharpless, K. B.; Lauer, R. F. J . Am. Chem. Soc. 1973, 95, 2697.
(9) The Chemistry of Organic Selenium and Tellurium Compounds;
Patai, S., Ed.; The Chemistry of Functional Groups; J ohn Wiley &
Sons: New York, 1987; Vol. 2, Chapters 3, 16, and 17.
(10) (a) Pfenninger, J .; Heuberger, C.; Graf, W. Helv. Chim. Acta
1980, 63, 2328. (b) Boger, D. L.; Mathvink, R. J . J . Org. Chem. 1992,
57, 1429. (c) Bachi, M. D.; Bosch, E. J . Org. Chem. 1992, 57, 4696. (d)
Clive, D. L. J .; Yang, W. Chem. Commun. 1996, 1605. (e) Barrett, A.
G. M.; Kwon, H.; Wallace, E. M. J . Chem. Soc., Chem. Commun. 1993,
1760. (f) Haraguchi, K. Tanaka, H.; Miyasaka, T. Tetrahedron Lett.
1990, 31, 227. (g) Ryu, I.; Kusano, K.; Masumi, N.; Yamazaki, H.;
Ogawa, A.; Sonoda, N. Tetrahedron Lett. 1990, 31, 6887.
(11) Hartwig, W. Tetrahedron 1983, 39, 2609.
(1) There are only two reports of SAM formation by organoselenium
compounds on gold: (a) Samant, M. G.; Brown, C. A.; Gordon, J . G.,
II. Langmuir 1992, 8, 1615. (b) Dishner, M. H.; Hemminger, J . C.;
Feher, F. J . Langmuir 1997, 13, 4788.
(2) (a) Tour, J . M.; J ones, L., II; Pearson, D. L.; Lamba, J . J . S.;
Burgin, T. P.; Whitesides, G. M.; Allara, D. L.; Parikh, A. N.; Atre, S.
V. J . Am. Chem. Soc. 1995, 117, 9529. (b) Bumm, L. A.; Arnold, J . J .;
Cygan, M. T.; Dunbar, T. D.; Burgin, T. P.; J ones, L., II; Allara, D. L.;
Tour, J . M.; Weiss, P. S. Science 1996, 271, 1705.
(3) Organic Selenium Compounds: Their Chemistry and Biology;
Klayman, D. L., Gu¨nther, W. H. H., Eds.; The Chemistry of Organo-
metallic Compounds; J ohn Wiley & Sons: New York, 1973; p 73.
(4) While, to our knowledge, no accounts exist in the literature
demonstrating addition of
a diselenide to a Pd(0) complex, the
corresponding reaction has been reported for disulfides (Zanella, R.;
Ros, R.; Graziani, M. Inorg. Chem. 1973, 12, 2736) and ditellurides
(Chia, L.-Y.; McWhinnie, W. R. J . Organomet. Chem. 1978, 148, 165).
(12) Testaferri, L.; Tiecco, M.; Tingoli, M.; Chianelli, D. Tetrahedron
1986, 42, 4577.
S0022-3263(97)02144-0 CCC: $15.00 © 1998 American Chemical Society
Published on Web 03/17/1998

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2398 J . Org. Chem., Vol. 63, No. 7, 1998
Notes
Sch em e 2
Ta ble 1. Selected Da ta for P r otected Alk yl- a n d
Ar ylselen ols
Sch em e 3
compd
13Ca
77Seb
IRc
4
5
6
7
8
163.80
163.95
163.92
167.63
167.54
167.65
198.09
198.12
197.85
162.32
166.09
195.71
162.62
166.14
196.90
390.63
390.66
390.77
393.66
393.63
393.69
559.72
559.76
559.47
519.90
509.54
667.00
519.82
510.43
664.12
1656, 1662
1655, 1663
1656, 1662
1717
1718
1718
1715
1715
1717
1665
1727
1709
1669
1726
with K2CO3 in THF/H2O to give selenolates that add to
phenylpropionitrile to give selenocinnamonitriles.13 There-
fore, further developments on the formation and hydroly-
sis of protected selenols is warranted.
9
10
11
12
13
14
15
16
17
18
Resu lts a n d Discu ssion
P r otected Selen ol Syn th eses. Utilizing the method
of Gladysz,14 lithium triethylborohydride reduction of
elemental selenium followed by quenching with alkyl
halides leads to formation of the dialkyl diselenides 1-3.
Unfortunately, a significant amount (5-15%) of the
corresponding dialkyl selenide (R2Se) is also produced in
this reaction; however, this does not interfere in the
subsequent reductive cleavage of the dialkyl diselenides
since the selenides are unreactive toward LiHBEt3.
Therefore, treatment of crude 1-3 with LiHBEt3 followed
by reaction with diethylcarbamyl chloride, ethyl chloro-
formate, or acetyl chloride yields the corresponding alkyl
selenocarbamates (4-6), selenocarbonates (7-9), and
selenoacetates (10-12), respectively (Scheme 1). Pro-
tected arylselenols can also be readily prepared by
employing the method outlined in Schemes 2 and 3.
Lithium-halogen exchange from an aryl halide, followed
by selenium insertion and finally quenching with the
protecting group chloride affords compounds 13-18. All
yields are unoptimized. All of the compounds synthesized
have been characterized by 1H, 13C, and 77Se NMR, FTIR,
and HRMS. Selected data for the protected alkyl and
aryl selenols are listed in Table 1.
P r otectin g Gr ou p Sta bility. All three of the pro-
tecting groups studied were quite stable to both air and
water. As expected, the selenocarbamates are signifi-
cantly more robust than the selenocarbonates and sele-
noacetates. For example, compound 13 is unaffected by
NH4OH, hydrazine sulfate, sodium borohydride, tetrabu-
tylammonium borohydride, tetrabutylammonium fluo-
ride, tetrabutylammonium hydroxide, sodium azide, and
N,N-(dimethylamino)pyridine. Only sodium hydroxide
effected removal of the diethylcarbamyl group with
concomitant formation of the corresponding diselenide.
In contrast, compounds 14 and 15 are smoothly depro-
1715
a
Chemical shift of carbonyl carbon in ppm relative to TMS.
b
Chemical shift in ppm relative to Me2Se in CDCl3 (60% v/v).
c Stretching frequency in cm-1 of carbonyl group (KBr pellet).
Sch em e 4
tected by treatment with aqueous NH4OH in THF
(Scheme 4). It has previously been reported that sele-
noesters can be cleaved using n-BuNH2 in EtOH.15
Attem p ted P d /Cu -Ca ta lyzed Cou p lin g of P r o-
tected Ar yl Selen ols. Despite their air and water
stability, 13-15 do not undergo Pd/Cu-catalyzed cross
coupling. Repeated attempts at coupling 13, 14, or 15
with (trimethylsilyl)acetylene under typical Sonogashira
coupling conditions16 were unsuccessful. Employing a
number of catalysts, including (Ph3P)2PdCl2, Pd(dba)2,
(PhCN)2PdCl2, and (NMDPP)2PdCl2,17 all in the presence
of CuI, at concentrations up to 10 mol % in a variety of
solvents (C6H6, THF, CH3CN) or in neat base (NEt3,
i-Pr2NEt) gave only unreacted starting material with
some unidentifiable impurities.
(15) Mautner, H. G.; Chu, S.-H.; Gu¨nther, W. H. H. J . Am. Chem.
Soc. 1963, 85, 3458.
(13) Zhao, C.-Q.; Huang, X. Synth. Commun. 1996, 26, 3607.
(14) Gladysz, J . A.; Hornby, J . L.; Garbe, J . E. J . Org. Chem. 1978,
43, 1204.
(16) Sonogashira, K.; Tohda, H.; Hagihara, N. Tetrahedron Lett.
1975, 4467.
(17) NMDPP ) (+)-neomenthyldiphenylphosphine.

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Notes
J . Org. Chem., Vol. 63, No. 7, 1998 2399
26.77, 22.70, 14.12, 14.01, 13.23; 77Se NMR (CDCl3) δ 390.66;
HRMS (EI) calcd for C21H43NOSe m/e 405.2510, found 405.2523
(M+).
Su m m a r y
We have prepared a series of alkyl and aryl seleno-
carbamates, selenocarbonates, and selenoacetates by
either reductive cleavage of the corresponding diselenide
or lithium-halogen exchange from an aryl halide and
selenium insertion, followed by capping with the ap-
propriate protecting group. Deprotection of these pro-
tected selenols was investigated, and the selenocarbam-
ates were found to be significantly more robust than the
other protecting groups. The selenocarbamates were
stable to a variety of reducing agents and nucleophiles
but were efficiently deprotected by NaOH. The seleno-
carbonates and selenoacetates were smoothly deprotected
by treatment with aqueous NH4OH. Unfortunately, Pd/
Cu-catalyzed coupling reactions employing these protect-
ing groups were unsuccessful. Despite this drawback,
these protecting groups offer advantages over diselenides
and selenocyanates in their ease of synthesis and re-
moval, as well as their applicability to a wide variety of
compounds such as R,ω-diselenols.
Se-n -Octadecyl-N,N-dieth ylselen ocar bam ate (6). Lithium
triethylborohydride (1.0 mL of a 1.0 M solution in THF, 1.0
mmol), dioctadecyl diselenide (0.332 g, 0.5 mmol), THF (15 mL),
and N,N-diethylcarbamyl chloride (0.15 mL, 1.2 mmol) afforded
0.281 g (65%) of 6 as a pale yellow liquid: IR (KBr) 2923, 2851,
1662, 1656, 1401, 1383, 1244, 1217, 1110, 845 cm-1 1H NMR
;
(CDCl3) δ 3.395 (br q, J ) 6.8 Hz, 2 H), 3.270 (br q, J ) 6.6 Hz,
2 H), 2.884 (t, J ) 7.4 Hz, 2 H), 1.664 (pent, J ) 7.4 Hz, 2 H),
1.221 (br overlapping m, 36 H), 0.845 (t, J ) 7.0 Hz, 3 H); 13C
NMR (CDCl3) δ 163.92, 43.07, 41.87, 31.94, 30.96, 30.12, 29.71,
29.67, 29.62, 29.57, 29.38, 29.18, 26.77, 22.70, 14.13, 14.01, 13.23;
77Se NMR (CDCl3) δ 390.77; HRMS (EI) calcd for C23H47NOSe
m/e 433.2823, found 433.2817 (M+).
Se-n -Dod ecyl-O-eth ylselen oca r bon a te (7). Lithium tri-
ethylborohydride (2.0 mL of a 1.0 M solution in THF, 2.0 mmol),
didodecyl diselenide (0.497 g, 1.0 mmol), THF (10 mL), and ethyl
chloroformate (0.21 mL, 2.2 mmol) afforded 0.474 g (74%) of 7
as a colorless liquid: IR (KBr) 2923, 2854, 1717, 1384, 1124,
1
1014, 835 cm-1; H NMR (CDCl3) δ 4.271 (q, J ) 7.1 Hz, 2 H),
2.863 (t, J ) 7.4 Hz, 2 H), 1.702 (pent, J ) 7.4 Hz, 2 H), 1.348
(br m, 2 H), 1.286 (t, J ) 7.1 Hz, 3 H), 1.232 (br s, 16 H), 0.855
(t, J ) 7.0 Hz, 3 H); 13C NMR (CDCl3) δ 167.63, 63.69, 31.92,
30.59, 29.81, 29.64, 29.63, 29.59, 29.50, 29.35, 29.08, 27.20, 22.69,
14.34, 14.11; 77Se NMR (CDCl3) δ 393.66; HRMS (EI) calcd for
Exp er im en ta l P r oced u r es
C
15H30O2Se m/e 322.1411, found 322.1404 (M+).
Gen er a l Meth od s. All reactions were performed under a
dry, nitrogen atmosphere using standard air-sensitive tech-
niques unless otherwise stated. Anhydrous diethyl ether and
tetrahydrofuran (THF) were distilled from sodium benzophenone
ketyl. Hexanes were distilled prior to use. Silica gel was grade
60 (230-400 mesh, EM Science), and silica gel plates were 250
µm thick K6F grade (Whatman) and were used as received. Gray
selenium powder (99.5+%, 200 mesh, Acros) was used as
received. Didodecyl diselenide, dihexadecyl diselenide, and
dioctadecyl diselenide were prepared by the method of Gladysz14
and contained 5-15% of the corresponding selenide. A number
of the products were highly viscous liquids or oils so the IR
spectra were obtained by dissolving the material in a minimal
amount of a suitable solvent, adding the solution to KBr,
evaporating the solvent, and then forming a pellet.
Gen er a l P r oced u r e for t h e Syn t h esis of P r ot ect ed
Alk ylselen ols. Lithium triethylborohydride (2 equiv) was
added dropwise to a stirred solution of the diselenide in THF at
room temperature. Gas was evolved, and the solution changed
from yellow to colorless. After the solution was stirred for at
least 15 min, the protecting group chloride was added dropwise.
After being stirred for at least 1 h at room temperature, the
solution was poured into water and extracted with hexanes and
ether. Purification was achieved by flash chromatography on
silica gel eluting with hexanes.
Se-n -Hexa d ecyl-O-eth ylselen oca r bon a te (8). Lithium tri-
ethylborohydride (1.0 mL of a 1.0 M solution in THF, 1.0 mmol),
dihexadecyl diselenide (0.304 g, 0.5 mmol), THF (15 mL), and
ethyl chloroformate (0.12 mL, 1.26 mmol) afforded 0.274 g (73%)
of 8 as a colorless liquid: IR (KBr) 2923, 2851, 1718, 1383, 1124,
1
1015, 835 cm-1; H NMR (CDCl3) δ 4.273 (q, J ) 7.2 Hz, 2 H),
2.865 (t, J ) 7.4 Hz, 2 H), 1.704 (pent, J ) 7.4 Hz, 2 H), 1.349
(br m, 2 H), 1.288 (t, J ) 7.1 Hz, 3 H), 1.231 (br s, 24 H), 0.855
(t, J ) 7.0 Hz, 3 H); 13C NMR (CDCl3) δ 167.54, 63.76, 32.02,
30.67, 29.90, 29.76, 29.68, 29.59, 29.46, 29.18, 27.32, 22.81, 14.46,
14.24; 77Se NMR (CDCl3) δ 393.63; HRMS (EI) calcd for
C
19H38O2Se m/e 378.2037, found 378.2045 (M+).
Se-n -Octa d ecyl-O-eth ylselen oca r bon a te (9). Lithium tri-
ethylborohydride (1.0 mL of a 1.0 M solution in THF, 1.0 mmol),
dioctadecyl diselenide (0.332 g, 0.50 mmol), THF (15 mL), and
ethyl chloroformate (0.12 mL, 1.26 mmol) afforded 0.212 g (52%)
of 9 as a colorless liquid: IR (KBr) 2924, 2853, 1718, 1385, 1124,
1
1014, 835 cm-1; H NMR (CDCl3) δ 4.269 (q, J ) 7.1 Hz, 2 H),
2.861 (t, J ) 7.4 Hz, 2 H), 1.702 (pent, J ) 7.4 Hz, 2 H), 1.347
(br m, 2 H), 1.285 (t, J ) 7.1 Hz, 3 H), 1.229 (br s, 24 H), 0.855
(t, J ) 7.0 Hz, 3 H); 13C NMR (CDCl3) δ 167.65, 63.71, 31.94,
30.59, 29.82, 29.71, 29.68, 29.65, 29.60, 29.51, 29.38, 29.09, 27.22,
22.71, 14.35, 14.13; 77Se NMR (CDCl3) δ 393.69; HRMS (EI) calcd
for C21H42O276Se m/e 402.2377, found 402.2378 (M+).
n -Dod ecylselen oa ceta te (10). Lithium triethylborohydride
(8.0 mL of a 1.0 M solution in THF, 8.0 mmol), didodecyl
diselenide (1.99 g, 4.0 mmol), THF (50 mL), and acetyl chloride
(0.64 mL, 9.0 mmol) afforded 1.59 g (68%) of 10 as a colorless
Se-n -Dod ecyl-N,N-d ieth ylselen oca r ba m a te (4). Lithium
triethylborohydride (2.0 mL of a 1.0 M solution in THF, 2.0
mmol), didodecyl diselenide (0.497 g, 1.0 mmol), THF (10 mL),
and N,N-diethylcarbamyl chloride (0.28 mL, 2.2 mmol) afforded
0.492 g (71%) of 4 as a colorless liquid: IR (KBr) 2923, 2853,
liquid: IR (KBr) 2923, 2851, 1715, 1383, 1105, 942, 721 cm-1
;
1H NMR (CDCl3) δ 2.874 (t, J ) 7.4 Hz, 2 H), 2.372 (t, J Se-H
)
1662, 1656, 1401, 1384, 1244, 1218, 1110, 846 cm-1 1H NMR
;
4.0 Hz, 3 H), 1.633 (pent, J ) 7.4 Hz, 2 H), 1.229 (br s, 18 H),
0.853 (t, J ) 6.9 Hz, 3 H); 13C NMR (CDCl3) δ 198.09, 34.85,
31.92, 30.45, 29.95, 29.64, 29.59, 29.50, 29.35, 29.10, 26.03, 22.70,
14.12; 77Se NMR (CDCl3) δ 559.72; HRMS (EI) calcd for
C14H28OSe m/e 292.1305, found 292.1307 (M+).
n -Hexa d ecylselen oa ceta te (11). Lithium triethylborohy-
dride (5.0 mL of a 1.0 M solution in THF, 5.0 mmol), dihexadecyl
diselenide (1.52 g, 2.5 mmol), THF (20 mL), and acetyl chloride
(0.43 mL, 6.0 mmol) afforded 1.27 g (73%) of 11 as a colorless
liquid that solidified upon standing: IR (KBr) 2923, 2851, 1715,
1383, 1105, 942, 722 cm-1; 1H NMR (CDCl3) δ 2.877 (t, J ) 7.4
Hz, 2 H), 2.376 (t, J Se-H ) 4.0 Hz, 3 H), 1.636 (pent, J ) 7.2 Hz,
2 H), 1.231 (br s, 26 H), 0.857 (t, J ) 6.9 Hz, 3 H); 13C NMR
(CDCl3) δ 198.12, 34.86, 31.94, 30.46, 29.96, 29.71, 29.68, 29.61,
29.51, 29.38, 29.11, 26.04, 22.71, 14.14; 77Se NMR (CDCl3) δ
559.76; HRMS (EI) calcd for C18H36OSe m/e 348.1931, found
348.1932 (M+).
(CDCl3) δ 3.386 (br q, J ) 6.4 Hz, 2 H), 3.262 (br q, J ) 6.4 Hz,
2 H), 2.794 (t, J ) 7.4 Hz, 2 H), 1.657 (pent, J ) 7.4 Hz, 2 H),
1.210 (broad overlapping multiplets, 24 H), 0.838 (t, J ) 7.0 Hz,
3 H); 13C NMR (CDCl3) δ 163.80, 43.14, 41.93, 32.01, 31.03,
30.20, 29.73, 29.70, 29.65, 29.45, 29.27, 26.87, 22.80, 14.24, 14.12,
13.33; 77Se NMR (CDCl3) δ 390.63; HRMS (EI) calcd for C17H35
-
NOSe m/e 349.1884, found 349.1886 (M+).
Se-n -Hexadecyl-N,N-dieth ylselen ocar bam ate (5). Lithium
triethylborohydride (2.0 mL of a 1.0 M solution in THF, 2.0
mmol), dihexadecyl diselenide (0.609 g, 1.0 mmol), THF (10 mL),
and N,N-diethylcarbamyl chloride (0.26 mL, 2.05 mmol) afforded
0.588 g (73%) of 5 as a yellow liquid: IR (KBr) 2923, 2851, 1663,
1655, 1400, 1244, 1215, 1110, 846 cm-1; 1H NMR (CDCl3) δ 3.385
(q, J ) 6.9 Hz, 2 H), 3.259 (q, J ) 6.9 Hz, 2 H), 2.875 (t, J ) 7.4
Hz, 2 H), 1.655 (pent, J ) 7.4 Hz, 2 H), 1.333 (m, 2 H), 1.210 (br
s, 24 H), 1.164 (br t, J ) 6.8 Hz, 3 H), 1.108 (br t, J ) 7.0 Hz, 3
H), 0.837 (t, J ) 7.0 Hz, 3 H); 13C NMR (CDCl3) δ 163.95, 43.07,
41.87, 31.93, 30.95, 30.12, 29.70, 29.66, 29.61, 29.56, 29.37, 29.18,
n -Octa d ecylselen oa ceta te (12). Lithium triethylborohy-
dride (5.0 mL of a 1.0 M solution in THF, 5.0 mmol), dioctadecyl

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2400 J . Org. Chem., Vol. 63, No. 7, 1998
Notes
diselenide (1.66 g, 2.5 mmol), THF (25 mL), and acetyl chloride
(0.43 mL, 6.0 mmol) afforded 0.531 g (28%) of 12 as a white,
crystalline solid: IR (KBr) 2923, 2853, 1717, 1384, 1105, 942,
cm-1; 1H NMR (CDCl3) δ 7.676 (d, J ) 8.1 Hz, 2 H), 7.201 (d, J
) 8.4 Hz, 2 H), 2.450 (t, J Se-H ) 4.0 Hz, 3 H); 13C NMR (CDCl3)
δ 195.71, 138.51, 137.36, 126.31, 95.63, 34.19; 77Se NMR (CDCl3)
δ 667.00; HRMS (EI) calcd for C8H7IO76Se m/e 321.8734, found
321.8723 (M+).
1
722 cm-1; H NMR (CDCl3) δ 2.861 (t, J ) 7.4 Hz, 2 H), 2.355
(t, J Se-H ) 4.0 Hz, 3 H), 1.623 (pent, J ) 7.2 Hz, 2 H), 1.221 (br
s, 30 H), 0.845 (t, J ) 6.9 Hz, 3 H); 13C NMR (CDCl3) δ 197.85,
34.79, 31.95, 30.48, 29.97, 29.73, 29.70, 29.67, 29.62, 29.53, 29.40,
29.13, 25.99, 22.71, 14.13; 77Se NMR (CDCl3) δ 559.47; HRMS
(EI) calcd for C20H40OSe m/e 376.2244, found 376.2236 (M+).
Gen er a l P r oced u r e for th e Syn th esis of P r otected Ar yl-
selen ols. tert-Butyllithium (2 equiv/halide) was added dropwise
to a stirred solution of the aryl halide in THF at -78 °C. After
the solution was stirred for at least 15 min, gray selenium
powder was added in one portion. After being stirred for at least
5 min at -78 °C, the solution was allowed to warm to 0 °C and
then, if necessary, to room temperature until all of the selenium
was consumed. The solution was cooled to -78 °C, and the
protecting group chloride was added dropwise. The reaction
mixture was warmed to room temperature. After being stirred
for at least 1 h at room temperature, the solution was poured
into water and extracted with ether or CH2Cl2.
1,4-[Bis(N,N-d ieth ylselen oca r ba m yl)]ben zen e (16). tert-
Butyllithium (19.4 mL of a 1.65 M solution in pentane, 32.0
mmol), 1,4-diiodobenzene (2.64 g, 8.0 mmol), THF (30 mL),
selenium powder (1.27 g, 16.1 mmol), and N,N-diethylcarbamyl
chloride (2.25 mL, 17.8 mmol) afforded 2.50 g (72%) of 16 as a
golden yellow solid: IR (KBr) 2972, 2930, 1669, 1402, 1241, 1210,
1112, 1008, 837, 806 cm-1 1H NMR (CDCl3) δ 7.550 (s, 4 H),
;
3.50-3.25 (m, 8 H), 1.35-1.05 (m, 12 H); 13C NMR (CDCl3) δ
162.62, 136.98, 127.81, 43.29, 42.50, 14.22, 13.21; 77Se NMR
(CDCl3) δ 519.82; HRMS (EI) calcd for C16H24N2O276Se2 m/e
436.0168, found 436.0152 (M+).
1,4-[Bis(O-eth ylselen oca r ba n oyl)]ben zen e (17). tert-Bu-
tyllithium (20.0 mL of a 1.61 M solution in pentane, 32.2 mmol),
1,4-diiodobenzene (2.64 g, 8.0 mmol), THF (30 mL), selenium
powder (1.27 g, 16.1 mmol), and ethyl chloroformate (1.80 mL,
19.0 mmol) afforded 1.37 g (45%) of 17 as white needles following
recrystallization from CH2Cl2/hexane at -10 °C: IR (KBr) 2995,
1718, 1132, 1009, 846, 831, 632 cm-1; 1H NMR (CDCl3) δ 7.584
(s, 4 H), 4.313 (q, J ) 7.1 Hz, 4 H), 1.309 (t, J ) 7.1 Hz, 6 H);
13C NMR (CDCl3) δ 166.14, 136.09, 127.48, 64.68, 14.36; 77Se
NMR (CDCl3) δ 510.43; HRMS (EI) calcd for C12H14O476Se2 m/e
375.9290, found 375.9281 (M+).
1-(N,N-Dieth ylselen oca r ba m yl)-4-iod oben zen e (13). tert-
Butyllithium (9.6 mL of a 1.65 M solution in pentane, 15.8
mmol), 1,4-diiodobenzene (2.64 g, 8.0 mmol), THF (25 mL),
selenium powder (0.633 g, 8.0 mmol), and N,N-diethylcarbamyl
chloride (1.1 mL, 8.7 mmol) afforded 1.37 g (45%) of 13 as a
yellow solid after flash column chromatography, first eluting
with hexanes and then with ethyl acetate and finally with
acetone: IR (KBr) 2972, 2931, 1665, 1403, 1239, 1210, 1110, 997,
4,4′-Bip h en yl-1-selen oa ceta te (18). tert-Butyllithium (5.4
mL of a 1.92 M solution in pentane, 10.4 mmol), 4-bromobiphenyl
(1.21 g, 5.2 mmol), THF (30 mL), selenium powder (0.411 g, 5.2
mmol), and acetyl chloride (0.44 mL, 6.2 mmol) afforded 0.280
g (20%) of 18 following purification by flash column chromatog-
raphy, eluting with 1:1 hexane/CH2Cl2: IR (KBr) 1715, 1385,
839, 800 cm-1 1H NMR (CDCl3) δ 7.597 (d, J ) 8.3 Hz, 2 H),
;
7.257 (d, J ) 8.3 Hz, 2 H), 3.50-3.15 (m, 4 H), 1.35-1.00 (m, 6
H); 13C NMR (CDCl3) δ 162.32, 138.40, 138.07, 126.61, 95.42,
43.30, 42.57, 14.21, 13.19; 77Se NMR (CDCl3) δ 519.90; HRMS
(EI) calcd for C11H14INO76Se m/e 378.9312, found 378.9301 (M+).
1-(O-Eth ylselen oca r ba n oyl)-4-iod oben zen e (14). tert-Bu-
tyllithium (12.5 mL of a 1.28 M solution in pentane, 16.0 mmol),
1,4-diiodobenzene (2.64 g, 8.0 mmol), THF (25 mL), selenium
powder (0.633 g, 8.0 mmol), and ethyl chloroformate (0.91 mL,
9.5 mmol) afforded 0.916 g (32%) of 14 as a yellow oil following
purification by flash column chromatography, eluting with 1:1
hexane/CH2Cl2: IR (KBr) 2980, 1727, 1472, 1123, 1001, 805
cm-1; 1H NMR (CDCl3) δ 7.667 (d, J ) 8.4 Hz, 2 H), 7.319 (d, J
) 8.4 Hz, 2 H), 4.310 (q, J ) 7.1 Hz, 2 H), 1.308 (t, J ) 7.1 Hz,
3 H); 13C NMR (CDCl3) δ 166.09, 138.40, 137.33, 125.84, 95.67,
64.76, 14.37; 77Se NMR (CDCl3) δ 509.54; HRMS (EI) calcd for
C9H9IO276Se m/e351.8839, found 351.8847 (M+).
1
1097, 945, 760 cm-1; H NMR (CDCl3) δ 7.573 (m, 6 H), 7.438
(m, 2 H), 7.364 (d, J ) 7.2 Hz, 1 H), 2.483 (t, J Se-H ) 3.9 Hz, 3
H); 13C NMR (CDCl3) δ 196.90, 141.95, 140.32, 136.09, 128.88,
128.14, 127.73, 127.21, 125.53, 34.13; 77Se NMR (CDCl3) δ
664.12; HRMS (EI) calcd for C14H12O76Se m/e 272.0080, found
272.0072 (M+).
Ack n ow led gm en t. This work was funded by the
Defense Advanced Research Projects Agency.
Su p p or tin g In for m a tion Ava ila ble: 1H NMR spectra for
compounds 4-12, 14, 15, and 17 and 13C NMR spectra for
compounds 13, 16, and 18 (15 pages). This material is
contained in libraries on microfiche, immediately follows this
article in the microfilm version of the journal, and can be
ordered from the ACS; see any current masthead page for
ordering information.
1-(Selen oa cetyl)-4-iod oben zen e (15). tert-Butyllithium
(8.4 mL of a 1.92 M solution in pentane, 16.1 mmol), 1,4-
diiodobenzene (2.64 g, 8.0 mmol), THF (25 mL), selenium powder
(0.633 g, 8.0 mmol), and acetyl chloride (0.68 mL, 9.6 mmol)
afforded 1.28 g (50%) of 15 following purification by flash column
chromatography, eluting first with hexane and then with
CH2Cl2: IR (KBr) 1709, 1468, 1384, 1376, 1105, 1003, 947, 805
J O972144A