(Aryltelluro)formates as precursors of alkyl radicals: Thermolysis and photolysis of primary and secondary alkyl (aryltelluro)formates

Article abstract of DOI:10.1021/jo960838y

Alkyl (aryltelluro)formates are effective precursors of oxyacyl, methyl, and primary and secondary alkyl radicals. At room temperature, irradiation of a benzene solution of methyl (aryltelluro)-formates 10-12, 2-methylpropyl (aryltelluro)formates 14 and 15, octyl (phenyltelluro)formate (17), cyclohexyl (aryltelluro)formates 19 and 20, 3β-cholestanyl (aryltelluro)formates 22 and 23, cholesteryl (phenyltelluro)formate (24) and benzyl (phenyltelluro)formate (27) with a 250-W low-pressure mercury lamp leads to the formation of oxyacyl radicals (34), which can be trapped by diphenyl diselenide to give the corresponding alkyl (phenylseleno)formates 13, 16, 18, 21, 24, 26, and 28 with excellent overall conversions. Thermolysis of these telluroformates at 160 °C in the dark leads to the formation of methyl and primary and secondary alkyl aryl tellurides 36-43 in excellent yields. Presumably, these transformations involve oxyacyl radicals, which undergo subsequent decarboxylation at the elevated temperature to afford alkyl radicals, which become involved in further radical chemistry. When 1-(benzylseleno)-5-hexyl (phenyltelluro)formate (44) was thermolysed under these conditions, 2-methylselenane (45) was observed as the sole selenium-containing product, demonstrating the synthetic utility of (aryltelluro)formates as alkyl radical precursors.

Full text of DOI:10.1021/jo960838y

5754
J . Org. Chem. 1996, 61, 5754-5761
(Ar yltellu r o)for m a tes a s P r ecu r sor s of Alk yl Ra d ica ls:
Th er m olysis a n d P h otolysis of P r im a r y a n d Secon d a r y Alk yl
(Ar yltellu r o)for m a tes
Mathew A. Lucas and Carl H. Schiesser*
School of Chemistry, The University of Melbourne, Parkville, Victoria, Australia 3052
Received May 7, 1996X
Alkyl (aryltelluro)formates are effective precursors of oxyacyl, methyl, and primary and secondary
alkyl radicals. At room temperature, irradiation of a benzene solution of methyl (aryltelluro)-
formates 10-12, 2-methylpropyl (aryltelluro)formates 14 and 15, octyl (phenyltelluro)formate (17),
cyclohexyl (aryltelluro)formates 19 and 20, 3â-cholestanyl (aryltelluro)formates 22 and 23,
cholesteryl (phenyltelluro)formate (24) and benzyl (phenyltelluro)formate (27) with a 250-W low-
pressure mercury lamp leads to the formation of oxyacyl radicals (34), which can be trapped by
diphenyl diselenide to give the corresponding alkyl (phenylseleno)formates 13, 16, 18, 21, 24, 26,
and 28 with excellent overall conversions. Thermolysis of these telluroformates at 160 °C in the
dark leads to the formation of methyl and primary and secondary alkyl aryl tellurides 36-43 in
excellent yields. Presumably, these transformations involve oxyacyl radicals, which undergo
subsequent decarboxylation at the elevated temperature to afford alkyl radicals, which become
involved in further radical chemistry. When 1-(benzylseleno)-5-hexyl (phenyltelluro)formate (44)
was thermolysed under these conditions, 2-methylselenane (45) was observed as the sole selenium-
containing product, demonstrating the synthetic utility of (aryltelluro)formates as alkyl radical
precursors.
In tr od u ction
of interest.2 Intramolecular reactions in which the leav-
ing radical is ejected from the molecule of interest usually
result in the formation of higher heterocycles. Recent
examples include the attack of alkyl and aryl radicals at
the sulfur atom in alkyl sulfides3 and sulfoxides4 and the
silicon atom in silanes,5 while we have developed methods
for the preparation of selenium-containing heterocycles
through the use of free-radical attack of alkyl,6 aryl,7
iminyl,8 and amidyl9 radicals at the selenium atom in
alkyl selenides.
Inter- and intramolecular free-radical homolytic sub-
stitution chemistry offers the synthetic chemist a con-
venient method for the synthesis of a variety of hetero-
atom-containing organic molecules.1-9 Intramolecular
group transfer and translocation chemistry in molecules
containing halo, phenylseleno, trialkylsilyl, and stannyl
moieties are representative of processes in which the
attacking and leaving radicals form part of the molecule
The choice of radical precursor in reactions involving
homolytic attack at selenium has proven to be crucial;
photolysis or thermolysis of thiohydroxamic esters in the
absence of chain carriers is effective in the preparation
of saturated selenium-containing heterocycles,6 while
iodides are required in reactions involving tributyltin
hydride or tris(trimethylsilyl)silane.7 Indeed, we dem-
onstrated recently that 2-(benzylseleno)-1-(2-iodophenyl)-
ethanol (1) reacts with tris(trimethylsilyl)silane to afford
benzo[b]selenophene, while the analogous bromide 2
affords mainly the selenosilane 3 under identical condi-
tions.7
X Abstract published in Advance ACS Abstracts, J uly 15, 1996.
(1) Intermolecular examples: (a) Curran, D. P.; Geib, S. J .; Kuo, L.
H. Tetrahedron Lett. 1994, 35, 6235. (b) Curran, D. P.; Eichenberger,
E.; Collis, M.; Roepel, M. G.; Thoma, G. J . Am. Chem. Soc. 1994, 116,
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Walter, R. I. J . Am. Chem. Soc. 1994, 116, 8937. (d) Curran, D. P.;
Martin-Esker, A. A.; Ko, S.-B.; Newcomb, M. J . Org. Chem. 1993, 58,
4691. (e) Tsai, Y.-M.; Tang, K.-H.; J iaang, W.-T. Tetrahedron Lett. 1993,
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(g) Curran, D. P.; Thoma, G. J . Am. Chem. Soc. 1992, 114, 4436. (h)
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1991, 32, 3515. (k) Newcomb, M.; Marquardt, D. J .; Kumar, M. U.
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Lett. 1990, 31, 5697. (m) Barth, F. O.; Yang, C. Tetrahedron Lett. 1990,
31, 1121. (n) Curran, D. P.; Chang, C.-T. J . Org. Chem. 1989, 54, 3140.
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Lett. 1988, 29, 6581.
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N. N.; Solodovnikov, S. P.; Ershov, V. V.; Kabachnik, M. I. Tetrahedron
1979, 35, 2471. (k) West, R.; Boudjouk, P. J . Am. Chem. Soc. 1973,
95, 3983. (l) Pitt, C. G.; Fowler, M. S. J . Am. Chem. Soc. 1968, 90,
1298.
(3) (a) Beckwith, A. L. J .; Duggan, S. A. M. J . Chem. Soc., Perkin
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Soc., Chem. Commun. 1990, 1408. (c) Beckwith, A. L. J .; Boate, D. R.
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K. F. J . Org. Chem. 1987, 52, 2256. (e) Baldwin, J . E.; Adlington, R.
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D. I.; Tyrrell, N. D.; Thomas, E. J . J . Chem. Soc., Chem. Commun.
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T. R. J . Am. Chem. Soc. 1966, 88, 4096.
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1986, 189.
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57. Benjamin, L. J .; Schiesser, C. H.; Sutej, K. Tetrahedron 1993, 49,
2557.
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S0022-3263(96)00838-9 CCC: $12.00 © 1996 American Chemical Society

(Aryltelluro)formates as Precursors of Alkyl Radicals
J . Org. Chem., Vol. 61, No. 17, 1996 5755
Sch em e 1
As part of ongoing studies, we required a method for
the generation of alkyl radicals from primary and sec-
ondary alcohols in the presence of the benzylseleno
moiety. Initial work involving the thionoformate func-
tionality as precursor was met with limited success.
Thus, 1-(benzylseleno)-5-hexyl (phenyloxy)thionoformate
(4), prepared under standard conditions,10 when treated
with tributyltin hydride in benzene (AIBN initiator)
afforded the stannyl selenide 5 as the sole isolated
product of reaction. Clearly, free-radical attack at the
thionoformate and subsequent â-scission are not com-
petitive with the homolytic substitution process at sele-
nium.
Recent high-level ab initio calculations performed in
our laboratories,11 together with available rate constant
data,12 suggest that alkyl tellurides react several orders
of magnitude more rapidly than alkyl selenides with
chain-carrying radicals such as tributylstannyl. In ad-
dition, Crich et al. demonstrated recently that acyl
tellurides (e.g., 6) are efficient precursors of acyl radicals
which often undergo further radical chemistry.1c Several
years ago, Pfenniger and co-workers showed that steroi-
dal (phenylseleno)formates (e.g., 7) react with tributyltin
hydride under appropriate conditions to afford decar-
boxylated products, while Bachi and Bosch demonstrated
that oxyacyl radicals derived from selenoformates un-
dergo homolytic addition chemistry.13
tication of reaction products) were prepared according to
the general procedure outlined in Scheme 1. The re-
quired alcohol 8 was reacted with a 20% solution of
phosgene in toluene to afford the corresponding chloro-
formate 9. The chloroformate was not isolated but
reacted with sodium aryltelluroate or sodium phenylse-
lenoate, prepared by the reduction of diphenyl ditellu-
ride,14 bis(4-fluorophenyl) ditelluride,14 bis(4-methoxy-
phenyl) ditelluride,15 or diphenyl diselenide with sodium
borohydride in tetrahydrofuran and methanol according
to the procedure of Crich et al.1c In this manner, the
telluro- and selenoformates 10-28 were prepared in 60-
98% yield.
There are few examples of the telluroformate func-
tional group in the literature.16 As such, the chemistry
of this novel functional group is largely unexplored. The
(aryltelluro)formates prepared in this study are light
sensitive and generally range from pale yellow to orange
in color. They appear to be stable in the dark at room
temperature for indefinite periods and are sufficiently
stable on exposure to background light to handle without
precaution for short periods.
Inspired by these reports, we began to explore the use
of (aryltelluro)formates (eq 19) as precursors of carbon-
centered radicals. We now report that these tellurofor-
mates are photochemically and thermally labile. Under
thermolytic conditions, radical formation is accompanied
by decarboxylation to afford primary and secondary alkyl
radicals, which undergo further reaction to give (aryl-
telluro)alkanes.
P h otoch em ica l Stu d ies. Given the photochemical
lability of aryltelluro esters,1c we began to explore the
photochemistry of (aryltelluro)formates. Initial studies
involved 2-methyl-1-propyl (phenyltelluro)formate (14),
which was readily prepared from commercially available
isobutyl chloroformate. When 14 in benzene-d6 (0.3 M)
in an NMR tube and in a water-cooled jacket was
irradiated with a 250-W low-pressure mercury lamp
1
(white light) for 2 d, H NMR spectrocopy revealed only
Resu lts a n d Discu ssion
starting material (14). To confirm that the oxyacyl
radical 29 was being formed, the experiment was re-
peated in the presence of diphenyl diselenide (1 equiv)
as a radical trap. 1H NMR spectroscopy indicated the
P r epar ation of Tellu r o- an d Selen ofor m ates. (Aryl-
telluro)formates and (phenylseleno)formates (for authen-
(10) Robins, M. J .; Wilson, J . S. J . Am. Chem. Soc. 1981, 103, 933.
(11) Schiesser, C. H.; Smart, B. A. Tetrahedron 1995, 51, 6051.
(12) Newcomb, M.; Sanchez, R. M.; Kaplan, J . J . Am. Chem. Soc.
1987, 109, 1195. Curran, D. P.; Martin-Esker, A. A.; Ko, S.-B.;
Newcomb, M. J . Org. Chem. 1993, 58, 4691.
(14) Haller, W. S.; Irgolic, K. J . J . Organomet. Chem. 1972, 38, 97.
(15) Morgan, G. T.; Kellett, R. E. J . Chem. Soc. 1926, 1080.
(13) Pfenniger, J .; Heuberger, C.; Graf, W. Helv. Chim. Acta 1980,
63, 2328. Bachi, M. D.; Bosch, E. Tetrahedron Lett. 1986, 27, 641.
Bachi, M. D.; Bosch, E. Heterocycles 1989, 28, 579.
(16) Marcel, S. F.; J ie, L. K.; Yan-Kit, C.; Chau, S. H.; Yan, B. F. Y.
J . Chem. Soc., Perkin Trans. 2 1991, 501. Inoue, T.; Takeda, T.; Kambe,
N.; Ogawa, A.; Ryu, I.; Sonoda, N. Organometallics 1994, 13, 4543.

5756 J . Org. Chem., Vol. 61, No. 17, 1996
Lucas and Schiesser
Sch em e 2
Ta ble 1. P h otolysis Ha lf-Lives of (Ar yltellu r o)for m a tes
(0.2 M) in th e P r esen ce of Dip h en yl Diselen id e in
Ben zen e a n d Selected 77Se a n d 125Te NMR Da ta
telluroformate
δ
125Te
product
δ
77Se
half-life (h)
10
11
12
14
15
17
19
20
22
23
25
27
771.4
765.3
751.9
768.9
760.3
767.8
771.6
769.9
770.2
768.7
771.9
784.2
13
13
13
16
16
18
21
21
24
24
26
28
506.3
15
19
20
11
18
14
9
11
17
15
13
6
505.2
505.6
509.3
F igu r e 1. Half-life dependence on concentration for photolysis
of (aryltelluro)formates 11, 14, 19, and 27 in the presence of
diphenyl diselenide in benzene.
509.1
fluoro and methoxy substituents is to increase the
reactions half-lives slightly. Only the steroidal system
22 appears to increase in rate with the introduction of
fluorine; however, the effect is minor. In our hands, the
preparation of diphenyl ditelluride from freshly-prepared
phenylmagnesium bromide and tellurium powder pre-
sented no difficulties (typical yield, 85%), and it is the
reagent of choice for the majority of our work.
509.8
511.3
formation of 2-methyl-1-propyl (phenylseleno)formate
(16, 90%) after 2 d. This result suggests that radical 29
is being generated on photolysis. In the absence of
diphenyl diselenide, decarboxylation to afford the alkyl
radical 30 or decarbonylation to afford the alkoxyl radical
31 is not competitive with recombination processes to
regenerate the telluroformate 14 (Scheme 2).
The photochemical transformation of 14 to 16 displays
the inverse concentration dependence expected for pho-
tochemical processes.17 At 0.37 M concentration, the
Inspection of Table 1 reveals that the 125Te chemical
shifts of the (aryltelluro)formates in this study fall
between 760 and 785 ppm, while the analogous 77Se shifts
associated with the selenoformates were measure to
range from 505 to 512 ppm. Reaction half-lives at 0.2 M
were measured to be about 15 h for the methyl-
substituted (phenyltelluro)formate 10 between 11 and 14
h for the primary alkyl systems 15 and 17, about 10 h
for the (secondary) cyclohexyl (phenyltelluro)formate (19),
and about 6 h in the case of benzyl (phenyltelluro)formate
(27), with an inverse dependence on concentration in all
cases. Only the steroidal systems 22 and 25 were
observed to go against the trend, with slower rates of
transformation.
1
reaction half-life was determined to be about 15 h by H
NMR spectroscopy. As the concentration was reduced
to 0.25, 0.20, 0.12, and 0.07 M, the half-life was observed
to decrease to 13, 11, 8, and 7 h, respectively.
Similar results are obtained for methyl (phenyltelluro)-
formate (10), 1-octyl (phenyltelluro)formate (17), cyclo-
hexyl (phenyltelluro)formate (19), 3â-cholestanyl (phen-
yltelluro)formate (22), 3â-cholesteryl (phenyltelluro)-
formate (25), and benzyl (phenyltelluro)formate (27).
Table 1 summarizes the half-life data at 0.2 M for the
photochemical reaction of the telluroformates in this
study with diphenyl diselenide as well as 77Se and 125Te
NMR chemical shifts of the products and reactants, while
Figure 1 displays the half-life concentration dependence
for a representative set of telluroformates.
Due to their ease of preparation, substituted aryl
tellurides are often used as free-radical precursors.1c,18
Of particular significance has been the use of the 4-fluo-
rophenyl (4-FPh)- and 4-methoxyphenyl (4-MeOPh)-
substituted tellurides. To assess the effect of substitu-
ents on the progress of these photochemical reactions,
several [(4-fluorophenyl)telluro]formates (11, 15, 20, and
23) and methyl [(4-methoxyphenyl)telluro]formate (12)
were reacted under the previously described reaction
conditions. As can be seen in Table 1, the effect of both
Benzyl (phenyltelluro)formate (27) was observed to
give products other than the corresponding selenoformate
28 under these photolytic conditions. The 1H NMR
spectrum of the reaction mixture obtained after 27 (0.04
M) was irradiated for 24 h revealed the presence of benzyl
(phenylseleno)formate (28), benzyl phenyl selenide19 (32),
and benzyl formate (33) in approximately equal quanti-
ties by comparison with authentic samples. While 28
presumably arises by reaction of the intermediate oxyacyl
radical with diphenyl diselenide, the presence of 33
clearly indicates that decarboxylation to afford the stable
benzyl radical and subsequent reaction with diphenyl
diselenide is competitive in this case. The formate 33
presumably arises through hydrogen abstraction by the
oxyacyl radical from a reactive benzylic position. Inter-
estingly, formates are not observed in the remaining
examples in this study.
Ingold, Lusztyk, and co-workers recently reported20
that acyl radicals are less reactive than their alkyl
(17) Barlop, J . A.; Coyle, J . D. Excited States in Organic Chemistry;
Wiley-Interscience: Bristol, 1975.
(18) Barton, D. H. R.; Ramesh, M. J . Am. Chem. Soc. 1990, 112,
891. Barton, D. H. R.; Bridon, D.; Zard, S. Z. Tetrahedron Lett. 1984,
25, 5777. Barton, D. H. R.; Camara, J .; Cheng, X.; Gero, S. D.;
J aszberenyi, J . Cs.; Quiclet-Sire, B. Tetrahedron 1992, 48, 9261.
(19) Mitchell, R. H. Can. J . Chem. 1980, 58, 1398.
(20) Brown, C. E.; Neville, A. G.; Rayner, D. M.; Ingold, K. U.;
Lusztyk, J . Aust. J . Chem. 1995, 48, 363.

(Aryltelluro)formates as Precursors of Alkyl Radicals
J . Org. Chem., Vol. 61, No. 17, 1996 5757
Sch em e 3
counterparts and appear to be resonance stabilized, a
phenomenon which is readily observable in the infrared
spectra of the radicals in question. Acyl radicals, there-
fore, appear not to be the highly reactive species normally
associated with σ-radicals. With this in mind, we specu-
late that the photolytic reactivities reported in Table 1
are the result of hyperconjugative contributions by the
alkyl group to the overall structure of 34. Resonance
contributor 35 becomes more important as the alkyl
radical (R•) is stabilized by hyperconjugation or, in the
case of benzyl, by resonance.
In our laboratories, 77Se and 125Te NMR spectroscopy
is routinely used to assess the outcome of reactions
involving selenium- and tellurium-containing compounds.
The 77Se NMR spectrum of the reaction mixture obtained
after the photolysis of any of the telluroformates in this
study in the presence of diphenyl diselenide displays a
single signal in the range δ 505-512 as well as a single
signal in the range δ 261-287 (diphenyl diselenide at δ
464 is also observed). The former signal was shown to
correspond to the product (phenylseleno)formate by com-
parision with an authentic sample, while the latter was
assigned to the dichalcogenide cross-product (PhSeTeAr).
125Te NMR spectroscopy revealed a signal in the range δ
836-847 for this dichalcogenide.
To confirm the presence of the selenotelluride in the
reaction mixture, an equimolar mixture of diphenyl
diselenide and diphenyl ditelluride was dissolved in
benzene. 77Se and 125Te NMR spectroscopy revealed the
presence of PhSeTePh (77Se, δ 264; 125Te, δ 837) in
addition to diphenyl diselenide and diphenyl ditelluride.
It is well established that solutions of diselenides and
ditellurides undergo rapid statistical chalcogen scram-
bling.21 Similar experiments involving bis(4-fluorophen-
yl) ditelluride and bis(4-methoxyphenyl) ditelluride con-
firmed the presence the respective dichalcogenide (Ph-
SeTeAr) in reactions involving the (4-fluorophenyl)- and
[(4-methoxyphenyl)telluro]formates, respectively.22
In accordance with the mechanism proposed by Crich
et al. for telluro esters,1c it seems reasonable to suggest
that the telluroformates in this study are involved in a
chain mechanism in which homolytic substitution by
phenylseleno radicals at the tellurium atom in the
telluroformate plays an important role (Scheme 3). The
formation of the selenotelluride is a consequence of this
mechanism; its formation, however, can also be explained
on the basis of direct attack of the aryltelluro radical,
generated in the primary photolytic process, at diphenyl
diselenide.
Ta ble 2. Th er m olysis Ha lf-Lives of (Ar yltellu r o)for m a tes
(0.2 M) in Ben zen e a t 160 °C a n d Selected P r od u ct 125Te
NMR Da ta
telluroformate
product
δ
125Te
half-life
10
14
15
19
20
22
23
27
36a
37a
38
337.4
421.2
33 d
19 d
12 d
6 d
423.6
39b
40
nde
nde
6 d
41c
42
677.8, 591.4
674.2, 589.2
679.2
11 d
10 d
8 h
43d
a
b
d
Reference 28. Reference 23. c Reference 29. Reference 24.
e Not determined, see text.
conditions; however, decarboxylation or decarbonylation
would, once again, appear not to be competitive processes.
Pfenniger and co-workers report that temperatures of
140-160° are required for decarboxylation of oxyacyl
radicals derived from steroidal selenoformates.13 With
this in mind, the telluroformate 14 in benzene-d6 (0.2 M)
in a sealed NMR tube was heated at 160°. 1H NMR
spectrocopy revealed starting material 14 and 2-methyl-
1-(phenyltelluro)propane (37) in approximately equal
proportions after 19 d. The reaction appears to be
extremely clean, with smooth formation of the decar-
boxylated product under these conditions. When the
reaction was repeated using cyclohexyl (phenyltelluro)-
formate (19) as a representative secondary system at 0.2
M, the reaction half-life was determined to be about 6 d
by 1H NMR spectroscopy. Table 2 lists the reaction half-
lives for a representative set of (aryltelluro)formates
along with product 125Te NMR chemical shifts, which
were found to lie between 340 and 680 ppm, depending
on the alkyl substituent. We were unable to obtain a
125Te signal for either of the (aryltelluro)cyclohexanes 39
and 40, presumably due to problems associated with ring
inversion.23
Th er m a l Stu d ies. Having demonstrated that the
radicals 34 in this study generally fail to decarboxylate
or decarbonylate at room temperature, we set out to
explore the conditions under which these telluroformates
are effective as alkyl radical precursors. Once again,
2-methyl-1-propyl (phenyltelluro)formate (14) was chosen
as our initial substrate. When 14 in benzene-d6 (0.3 M)
in an NMR tube was heated at 80° (shielded from
1
background light) for 2 d, H NMR spectrocopy revealed
only starting material 14. In the presence of diphenyl
diselenide, 35% conversion to the selenoformate 16 was
observed after thermolysis for 22 d. It would appear that
the radical 29 is being generated under these thermolytic
(21) McFarlane, H. C. E.; McFarlane, W. J . Chem. Soc., Dalton
Trans. 1973, 2416.
(22) Measured NMR data. (4-FPh)TeSePh: 77Se δ 280.2; 125Te δ
847.1. (4-MeOPh)TeSePh: 77Se δ 286.5; 125Te δ 846.7.

5758 J . Org. Chem., Vol. 61, No. 17, 1996
Lucas and Schiesser
Sch em e 4
3â-cholestanyl (phenyltelluro)formate (22, 1.6 M) was
transformed into the epimeric mixture of 41 in 71% yield
(92% based on recovered starting material).25
Finally, we reacted 1-(benzylseleno)-5-hexyl (phenyl-
telluro)formate (44, 0.7 M) under these conditions. To
our delight, H NMR spectroscopy indicated the quanti-
tative formation of benzyl phenyl telluride (43) and
2-methylselenane26 (45), which was isolated as the di-
bromide26 46 in 74% yield.
1
F igu r e 2. Half-life dependence on concentration for ther-
molysis of cyclohexyl (phenyltelluro)formate (19) at 160 °C in
benzene.
Methyl (phenyltelluro)formate (10), 3â-cholestanyl
(phenyltelluro)formate (22), and benzyl (phenyltelluro)-
formate (27) were determined to have half-lives of 33 d,
11 d, and 8 h, respectively. The introduction of fluorine
(15, 20, and 23) appears to have only a marginal effect
on the rate of reaction (Table 2). All telluroformates
appear to decarboxylate smoothly at 160° to afford the
corresponding alkyl aryl tellurides 36-42, with the
exception of the benzyl system 27, which appeared to
produce substantial quantities of biphenyl and diphenyl
ditelluride in addition to benzyl phenyl telluride (43).
This is not surprising, as 43 is known to decompose
readily.24 The observed substrate reactivities are in
accord with those expected on the basis of the nature of
the intermediate alkyl radical.
Con clu sion s
By controlling the reaction conditions, alkyl (aryltel-
luro)formates can be employed as precursors of oxyacyl
or alkyl radicals. Photolysis at room temperature leads
to the formation of the oxyacyl radicals, which can be
trapped by diphenyl diselenide, while thermolysis at 160°
can be used as a method for the generation of methyl
and primary and secondary alkyl radicals, which become
involved in further radical chemistry. The synthetic
utility of (aryltelluro)formates as alkyl radical precursors
is demonstrated in the transformation of 1-(benzylse-
leno)-5-hexyl (phenyltelluro)formate (44) into 2-meth-
ylselenane (45).
3â-Cholestanyl (phenyltelluro)formate (22) and the
fluorinated derivative 23 yielded the corresponding 3-aryl-
tellurocholestanes25 41 and 43 as an epimeric mixture
(R:â ≈ 1:3.5), which is not surprising, given that the
intermediate 3-cholestanyl radical has two distinct faces
for attack.
Exp er im en ta l Section
Diphenyl ditelluride, bis(4-fluorophenyl) ditelluride, and bis-
(4-methoxyphenyl) ditelluride were prepared according to
published procedures.14,15 Diphenyl diselenide was purchased
from Fluka and used without further purification. Phosgene
was purchased from Fluka as a 20% solution in toluene (1.93
M). All melting points and boiling points are uncorrected.
NMR spectra were recorded in benzene-d6 unless otherwise
stated. Elemental analyses were carried out by Chemical and
Micro Analytical Services Pty. Ltd.
Sta n d a r d P r otocol (A) for th e P r ep a r a tion of (Ar yl-
tellu r o)for m a tes fr om Ch lor ofor m a tes. Meth yl (P h en -
yltellu r o)for m a te (10). Sodium borohydride (113 mg, 3.0
mmol) was added with stirring to a solution of diphenyl
ditelluride (420 mg, 1.0 mmol) in THF (30 mL). The reaction
vessel was purged with nitrogen, and methanol (∼250 µL) was
added dropwise until the red solution turned colorless (30 min).
When the evolution of hydrogen had ceased (∼60 min), methyl
chloroformate (208 mg, 2.2 mmol) was added via syringe, and
the resulting mixture was stirred for a further 60 min. Water
(10 mL) was added, and the mixture was extracted into ether
(3 × 50 mL). The combined ether extracts were dried (MgSO4),
and the solvent was removed in vacuo to afford a yellow oil.
Pure 10 (480 mg, 91%) was obtained after Ku¨gelrohr distil-
lation (50-60°/0.075 mmHg): 1H NMR δ 3.27 (3H, s), 6.95-
7.12 (3H, m), 7.74-7.77 (2H, m); 13C NMR δ 53.64, 113.76,
128.96, 129.58, 139.96, 156.78; 125Te NMR δ 771.4; IR ν (CdO)
(neat) 1711 cm-1; MS m/ z (relative intensity) 266 (M+, 10.1),
The thermolytic transformation of telluroformate into
alkyl telluride displays the expected concentration de-
pendence. We chose to explore this concentration de-
pendence for the reaction involving cyclohexyl (phenyl-
telluro)formate (19). At 160°, the reaction half-life varied
from 13 d (0.04 M) to 17 h (0.96 M) (Figure 2). These
data suggest that concentrations greater than about 0.5
M are required for synthetically viable reactions.
To test the synthetic viability of these telluroformates
as radical precursors, tellurides 39 and 41 were prepared
from the corresponding telluroformates 19 and 22. Thus,
cyclohexyl (phenyltelluro)formate (19) in benzene (1.0 M)
was heated in a sealed tube at 160° for 7 d. Solvent
evaporation and chromatography afforded (phenyltel-
luro)cyclohexane (39) in 85% yield. In similar fashion,
(23) Duddeck, H.; Wagner, P.; Billass, A. Magn. Reson. Chem. 1991,
29, 248.
(24) Comasseto, J . V.; Ferreira, J . T. B.; Fontanillas Val, J . A. J .
Organomet. Chem. 1984, 277, 261.
(25) 3R-(Phenyltelluro)cholestane has been reported previously:
Clive, D. L. J .; Chittattu, G. J .; Farina, V.; Kiel, W. A.; Menchen, S.
M.; Russell, C. G.; Singh, A.; Wong, C. K.; Curtis, N. J . J . Am. Chem.
Soc. 1980, 102, 4438.
(26) Morgan, G. T.; Burstall, F. H. J . Chem. Soc. 1929, 2197.

(Aryltelluro)formates as Precursors of Alkyl Radicals
J . Org. Chem., Vol. 61, No. 17, 1996 5759
222 (3), 207 (34), 92 (24), 77 (100). Anal. Calcd for C8H8O2-
Te: C, 36.43; H, 3.06. Found: C, 36.39; H, 3.10.
7.04 (3H, m), 7.95-7.80 (2H, m); 13C NMR δ 14.32, 23.00,
25.99, 28.98, 29.34, 29.43, 32.07, 67.98, 114.01, 128.90, 129.54,
140.01, 156.51; 125Te NMR δ 767.8; IR ν (CdO) (neat) 1716
cm-1; MS m/ z (relative intensity) 364 (M+, 1.8), 320 (0.50),
284 (2), 154 (8.0), 56 (100); HRMS calcd for C15H22O2Te
364.0689, found 364.0678.
Meth yl [(4-flu or op h en yl)tellu r o]for m a te (11) was pre-
pared according to the standard protocol (A) using bis(4-
fluorophenyl) ditelluride and methyl chloroformate. Ku¨gelrohr
distillation (50-60° /0.075 mmHg) afforded 11 as a yellow oil
(93%): 1H NMR δ 3.27 (3H, s), 6.56-6.62 (2H, m), 7.47-7.51
(2H, m); 13C NMR δ 53.75, 107.70, 116.92 (d, J ) 20.7 Hz),
142.34 (d, J ) 8.1 Hz), 156.82, 163.74 (d, J ) 247.7 Hz); 125Te
NMR δ 765.3; IR ν (CdO) (neat) 1711 cm-1; MS m/ z (relative
intensity) 283 (M+, 21.5), 225 (61), 239 (8), 130 (9), 95 (100);
HRMS calcd for C8H7O2TeF 282.9421, found 282.9426.
Meth yl [(4-m eth oxyp h en yl)tellu r o]for m a te (12) was
prepared according to the standard protocol (A) using bis(4-
methoxyphenyl) ditelluride and methyl chloroformate. Re-
crystallization from ethanol gave a light brown, low melting
solid (87%): 1H NMR δ 3.16 (3H, s), 3.27 (3H, s), 6.58 (2H, d,
J ) 9 Hz), 7.71 (2H, d, J ) 9 Hz); 13C NMR δ 53.55, 54.57,
103.23, 115.73, 142.28, 160.95; 125Te NMR δ 751.9; IR ν (CdO)
(neat) 1712 cm-1; MS m/ z (relative intensity) 296 (M+, 33.0),
237 (100), 222 (31), 167 (4), 122 (35). Anal. Calcd for C9H10O3-
Te: C, 36.80; H, 3.43. Found; C, 36.76; H, 3.38.
2-Meth yl-1-p r op yl (p h en yltellu r o)for m a te (14) was pre-
pared according to the standard protocol (A) using diphenyl
ditelluride and isobutyl chloroformate. Ku¨gelrohr distillation
(60-70°/0.08 mmHg) afforded 14 as a yellow oil (86%): 1H
NMR δ 0.60 (6H, d, J ) 6.9 Hz), 1.58 (1H, m), 3.82 (2H, d, J
) 6.6 Hz), 6.95-7.05 (3H, m), 7.78-7.81 (2H, m); 13C NMR δ
18.78, 28.05, 73.64, 113.97, 128.90, 129.53, 140.07, 156.45;
125Te NMR δ 768.9; IR ν (CdO) (neat) 1709 cm-1; MS m/ z
(relative intensity) 308 (M+, 3.6), 284 (0.2), 208 (12), 77 (48),
56 (100). Anal. Calcd for C11H14O2Te: C, 43.20; H, 4.61.
Found; C, 43.03; H, 4.70.
2-Meth ylp r op yl [(4-flu or op h en yl)tellu r o]for m a te (15)
was prepared according to the standard protocol (A) using bis-
(4-fluorophenyl) ditelluride and isobutyl chloroformate. Ku¨gel-
rohr distillation (60-70°/0.075 mmHg) afforded 15 as a yellow
oil (83%): 1H NMR δ 0.61 (6H, d, J ) 6.9 Hz), 1.59 (1H, m),
3.83 (2H, d, J ) 6.6 Hz), 6.58-6.64 (2H, m), 7.51-7.56 (2H,
m); 13C NMR δ 18.75, 28.05, 73.76, 107.99, 116.90 (d, J ) 21.2
Hz), 142.42 (d, J ) 7.6 Hz), 156.45, 163.71 (d, J ) 248.3 Hz);
125Te NMR δ 760.3; IR ν (CdO) (neat) 1711 cm-1; MS m/ z
(relative intensity) 325 (M+, 3.1), 225 (17), 130 (5), 95 (36), 56
(100); HRMS calcd for C11H13O2TeF 324.9891, found 324.9898.
Sta n d a r d P r otocol (B) for th e P r ep a r a tion of Tellu r o-
for m a tes fr om Alcoh ols. Cycloh exyl (P h en yltellu r o)-
for m a te (19). Sodium borohydride (261 mg, 6.9 mmol) was
added with stirring to a solution of diphenyl ditelluride (930
mg, 2.3 mmol) in THF (50 mL). The reaction vessel was
purged with nitrogen, and methanol (∼250 µL) was added
dropwise until the red solution turned colorless (30 min). In
a separate reaction vessel, 20% phosgene solution (15 mL, 29
mmol) was added via syringe to a solution of cyclohexanol (500
mg, 5.0 mmol) in THF (50 mL) under nitrogen. The solution
was stirred for a further 60 min and concentrated in vacuo to
approximately half the original volume. After purging with
nitrogen, the solution of the chloroformate was transferred via
cannula into the solution containing the sodium phenyltel-
luroate, and the resulting light yellow solution was stirred at
room temperature under nitrogen overnight. Water (10 mL)
was added, and the mixture was extracted with ether (3 × 50
mL). The combined ether extracts were dried (MgSO4), and
the solvent was removed in vacuo. The telluroformate 19 was
obtained as a yellow oil after flash chromatogaphy (hexane/
ethyl acetate 99:1) (1.35 g, 90%): 1H NMR δ 0.93-1.63 (10H,
m), 4.95 (1H, m), 6.93-7.02 (3H, m), 7.80-7.83 (2H, m); 13C
NMR δ 23.52, 25.32, 31.84, 77.09, 114.32, 128.82, 129.50,
139.95, 155.81; 125Te NMR δ 771.6; IR ν (CdO) (neat) 1709
cm-1; MS m/ z (relative intensity) 333 (M+, 0.5), 289 (0.7), 208
(7), 130 (1), 83 (100). Anal. Calcd for C13H16O2Te: C, 47.05,
H, 4.86. Found C, 46.93, H, 4.96.
Cycloh exyl [(4-flu or op h en yl)tellu r o]for m a te (20) was
prepared according to the standard protocol (B) using bis(4-
fluorophenyl) ditelluride and cyclohexanol. Flash chromatog-
raphy (hexane/ethyl acetate 99:1) afforded 20 as a yellow oil
(73%): 1H NMR δ 0.92-1.62 (10H, m), 4.94 (1H, m), 6.60 (2H,
m), 7.55 (2H, m); 13C NMR δ 23.52, 25.27, 31.84, 77.30, 108.27
(d, J ) 3.5 Hz), 116.88 (d, J ) 20.8 Hz), 142.33 (d, J ) 7.6
Hz), 155.84, 163.70 (d, J ) 247.7 Hz); 125Te NMR δ 769.9; IR
ν (CdO) (neat) 1709 cm-1; MS m/ z (relative intensity) 352 (M+,
0.3), 225 (11), 220 (3), 95 (25), 83 (100). Anal. Calcd for
C13H15O2TeF: C, 44.62; H, 4.32. Found: C, 44.65; H, 4.38.
3â-Ch olesta n yl (p h en yltellu r o)for m a te (22) was pre-
pared according to the standard protocol (B) using diphenyl
ditelluride and 3â-cholestanol. Recrystallization from ethanol
1
gave 22 as a white solid (70%): mp ) 126-127°; H NMR δ
0.35-1.98 (46H, m), 4.97 (1H, m), 6.96-7.02 (3H, m), 7.84-
7.87 (2H, m); 13C NMR δ 12.12, 12.30, 19.00, 21.43, 22.77,
23.03, 24.33, 24.50, 28.01, 28.40, 28.63, 28.68, 32.13, 34.54,
35.38, 35.56, 36.20, 36.64, 36.78, 39.91, 40.34, 42.83, 44.56,
54.17, 56.66, 78.34, 114.32, 128.86, 129.58, 139.90, 156.03; 125
-
Te NMR δ 770.2; IR ν (nujol) (CdO) 1710 cm-1; MS m/ z
(relative intensity) 578 (14.4), 409 (3), 371 (69), 245 (10), 95
(100), 81 (82). Anal. Calcd for C34H52O2Te: C, 65.83; H, 8.45.
Found: C, 65.91, H, 8.52.
3â-Ch olesta n yl [(4-flu or op h en yl)tellu r o]for m a te (23)
was prepared according to the standard protocol (B) using bis-
(4-fluorophenyl) ditelluride and 3â-cholestanol. Recrystalli-
zation from ethanol gave 23 as a white solid (75%): mp )
1
113.5-114.5°; H NMR δ 0.38-1.99 (46H, m), 4.97 (1H, m),
6.62 (2H, m), 7.59 (2H, m); 13C NMR δ 12.13, 12.30, 19.00,
21.44, 22.76, 23.03, 24.33, 24.50, 28.02, 28.40, 28.62, 28.68,
32.13, 34.56, 35.38, 35.56, 36.20, 36.64, 36.78, 39.91, 40.33,
42.84, 44.57, 54.18, 56.62, 56.66, 78.58, 108.30, 116.95 (d, J )
21.2 Hz), 142.24 (d, J ) 7.6 Hz), 155.98, 163.72 (d, J ) 247.2
Hz); 125Te NMR δ 768.7; IR ν (CdO) 1717 cm-1; MS m/ z
(relative intensity) 578 (0.35), 495 (6), 370 (36), 316 (14), 203
(10), 81 (100). Anal. Calcd for C34H51O2TeF: C, 63.97; H, 8.05.
Found: C, 63.93; H 8.29.
3â-Ch olester yl [(4-flu or op h en yl)tellu r o]for m a te (25)
was prepared according to the standard protocol (B) using
diphenyl ditelluride and cholesterol. Recrystallization from
ethanol afforded 25 as a white solid (80%): mp ) 127-128°;
1H NMR δ 0.64-2.48 (43H, m), 4.98 (1H, m), 5.25 (1H, m),
6.95-7.05 (3H, m), 7.82-7.86 (2H, m); 13C NMR δ 12.03, 19.04,
19.23, 21.26, 22.79, 23.05, 24.35, 24.56, 28.29, 28.40, 28.60,
32.03, 32.21, 36.19, 36.64, 37.07, 38.69, 39.91, 40.07, 42.53,
50.13, 56.49, 56.88, 74.25, 78.52, 114.29, 123.17, 128.88,
129.58, 139.41, 139.88, 155.91; 125Te NMR δ 771.9; IR ν (Nujol)
(CdO) 1717 cm-1; MS m/ z (relative intensity) (21 eV) 575 (1.7),
369 (100), 284, (4), 207 (17), 175 (14), 161 (34). Anal. Calcd
for C34H50O2Te: C, 66.04; H, 8.15. Found: C, 66.16; H 7.98.
Ben zyl (p h en yltellu r o)for m a te (27) was prepared ac-
cording to the standard protocol (B) using diphenyl ditelluride
and benzyl alcohol. Flash chromatography (hexane/ethyl
1
acetate 98:2) afforded 27 as an orange oil (60%); H NMR δ
4.96 (2H, s), 6.94-7.02 (8H, m), 7.73-7.75 (2H, m); 13C NMR
δ 69.23, 113.95, 128.51, 128.64, 128.71, 128.96, 129.56, 135.66,
140.01, 156.45; 125Te NMR δ 784.2; IR ν (neat) (CdO) 1709
cm-1; MS m/ z (relative intensity) 342 (M+, 0.94), 298 (3), 207
(16), 91 (100), 77 (61); HRMS calcd for C14H12O2Te 341.9907,
found 341.9922.
Sta n d a r d P r otocol (C) for th e P r ep a r a tion of (P h en -
ylselen o)for m a tes fr om Ch lor ofor m a tes. Meth yl (P h en -
ylselen o)for m a te (13). Sodium borohydride (148 mg, 3.9
mmol) was added with stirring to a solution of diphenyl
diselenide (400 mg, 1.3 mmol) in THF (30 mL). The reaction
vessel was purged with nitrogen, and methanol (∼250 µL) was
added dropwise until the yellow solution turned colorless (30
min). When the evolution of hydrogen had ceased (∼60 min),
methyl chloroformate (265 mg, 2.8 mmol) was added via
1-Octyl (p h en yltellu r o)for m a te (17) was prepared ac-
cording to the standard protocol (B) using diphenyl ditelluride
and 1-octanol. Flash chromatography (hexane/ethyl acetate
98:2) afforded 17 as a yellow oil (98%): 1H NMR δ 0.89 (3H, t,
J ) 7.2 Hz), 1.03-1.38 (12H,m), 4.03 (2H, t, J ) 6.9 Hz), 6.95-

5760 J . Org. Chem., Vol. 61, No. 17, 1996
Lucas and Schiesser
syringe, and the resulting mixture was stirred for a further 2
h. Water (10 mL) was added, and the mixture was extracted
into ether (3 × 50 mL). The combined ether extracts were
dried (MgSO4), and the solvent was removed in vacuo to afford
a yellow oil. Pure 13 (483 mg, 88%) was obtained as a pale
oil after Ku¨gelrohr distillation (40-50°/0.075 mmHg): 1H NMR
δ 3.22 (3H, s), 6.96-6.98 (3H, m), 7.53-7.54 (2H, m); 13C NMR
δ 54.15, 129.05, 129.36, 135.95, 166.62; 77Se NMR δ 506.3; IR
ν (CdO) (neat) 1724 cm-1; MS m/ z (relative intensity) 216 (M+,
30.3), 172 (23), 157 (100), 91 (33), 77 (66). Anal. Calcd for
C8H8O2Se: C, 44.67; H, 3.75. Found: C, 44.60; H, 3.82.
2-Meth yl-1-p r op yl (p h en ylselen o)for m a te (16) was pre-
pared according to the standard protocol (C) using diphenyl
diselenide and isobutyl chloroformate. Ku¨gelrohr distillation
(40-50°/0.075 mmHg) gave a pale yellow oil (85%): 1H NMR
δ 0.91 (6H, d, J ) 6.6 Hz), 1.96 (1H, m), 4.04 (2H, d, J ) 6.6
Hz), 7.34-7.38 (3H, m), 7.61-7.63 (2H, m); 13C NMR δ 18.85,
27.86, 74.17, 119.94, 128.99, 129.18, 135.75, 166.80; 77Se NMR
(3H, m), 7.63-7.66 (2H, m); 13C NMR δ 12.03, 19.03, 19.21,
21.25, 22.77, 23.03, 24.34, 24.55, 28.10, 28.39, 28.59, 32.02,
32.20, 36.18, 36.63, 36.99, 38.48, 39.91, 40.07, 42.53, 50.12,
56.49, 56.88, 78.85, 123.22, 126.99, 128.96, 129.36, 136.00,
139.31, 165.59; 77Se NMR δ 509.8; IR ν (Nujol) (CdO) 1720
cm-1; MS m/ z (relative intensity) 525 (1.6), 369 (100), 247 (8),
215 (6), 187 (3), 161 (20). Anal. Calcd for C34 H50 O2 Se: C,
71.68; H, 8.85. Found: C, 71.24; H, 8.96.
Ben zyl (p h en ylselen o)for m a te (28) was prepared accord-
ing to the standard protocol (D) using diphenyl diselenide and
benzyl alcohol. Vaccum chromatography (hexane/ethyl acetate
90:10) afforded pure 19 as a light yellow oil (90%), which
solidified on standing: mp ) 39-40°; 1H NMR δ 4.92 (2H, s),
6.96-7.05 (8H, m), 7.51-7.55 (2H, m); 13C NMR δ 69.65,
126.54, 128.58, 128.67, 128.71, 129.05, 129.35, 135.45, 136.04,
166.27; 77Se NMR δ 511.3; IR ν (CdO) (neat) 1714 cm-1; MS
m/ z (relative intensity) 248 (2.8), 157 (6), 105 (3), 91 (100),
77(13), 65 (13); HRMS calcd for C13H12Se 248.0104, found
248.0100.
δ 505.2; IR ν (CdO) (neat) 1726 cm-1
. Anal. Calcd for
C11H14O2Se: C, 51.37; H, 5.49. Found: C, 51.30; H, 5.47.
Sta n d a r d P r otocol (D) for th e P r ep a r a tion of Selen o-
for m a tes fr om Alcoh ols. Cycloh exyl (P h en ylselen o)-
for m a te (21). Sodium borohydride (182 mg, 4.8 mmol) was
added with stirring to a solution of diphenyl diselenide (500
mg, 1.6 mmol) in THF (50 mL). The reaction vessel was
purged with nitrogen, and methanol (∼250 µL) was added
dropwise until the red solution turned colorless (30 min). In
a separate reaction vessel, 20% phosgene solution (15 mL, 29
mmol) was added via syringe to a solution of cyclohexanol (353
mg, 3.5 mmol) in THF (50 mL) under nitrogen. The solution
was stirred for a further 60 min and concentrated in vacuo to
approximately half the original volume. After purging with
nitrogen, the solution of the chloroformate was transferred via
cannula into the solution containing the sodium phenylsele-
noate, and the resulting colorless solution was stirred at room
temperature under nitrogen overnight. Water (10 mL) was
added, and the mixture was extracted with ether (3 × 50 mL).
The combined ether extracts were dried (MgSO4), and the
solvent was removed in vacuo. The selenoformate 21 was
obtained as a yellow oil after flash chromatogaphy (hexane/
ethyl acetate 99:1) (878 mg, 97%): 1H NMR δ 0.92-1.65 (10H,
m), 4.87 (1H, m), 6.99-7.01 (3H, m), 7.60-7.63 (2H, m); 13C
NMR δ 23.48, 25.28, 31.63, 77.48, 120.35, 128.94, 129.31,
136.00, 165.44; 77Se NMR δ 509.3; IR ν (CdO) (neat) 1727
cm-1; MS m/ z (relative intensity) 238 (2.7), 197 (7), 158 (7),
105 (7), 83 (100). Anal. Calcd for C13H16O2Se: C, 55.13; H,
5.69. Found: C, 54.95; H, 5.61.
Sta n d a r d P r otocol (E) for th e F or m a tion of Alk yl Ar yl
Tellu r id es. 1-(4-F lu or op h en yl)-2-m eth ylp r op a n e (38).
Sodium borohydride (128 mg, 3.4 mmol) was added with
stirring to a solution of bis(4-fluorophenyl) ditelluride (500 mg,
1.1 mmol) in THF (40 mL). The reaction vessel was purged
with nitrogen and methanol (∼200 µL) was added dropwise
until the red solution turned colorless (30 min). When the
evolution of hydrogen had ceased (∼60 min), 1-bromo-2-
methylpropane (339 mg, 2.5 mmol) was added via syringe, and
the resulting mixture was stirred for a further 60 min. Water
(10 mL) was added, and the mixture was extracted into ether
(3 × 50 mL). The combined ether extracts were dried (MgSO4),
and the solvent was removed in vacuo to afford a yellow oil.
The telluride 38 (480 mg, 91%) was obtained after Ku¨gelrohr
distillation (40-50°/0.09 mmHg): 1H NMR δ 0.83 (6H, d, J )
6.6 Hz), 1.66 (1H, nonet, J ) 6.6 Hz), 2.57 (2H, d, J ) 6.6 Hz),
6.58 (2H, m), 7.44 (2H, m); 13C NMR δ 20.97, 23.87, 30.12,
106.02 (d, J ) 3.5 Hz), 116.60 (d, J ) 20.7 Hz), 141.00 (d, J )
7.6 Hz), 163.13 (d, J ) 245.7 Hz); 125Te NMR δ 423.73; MS
m/ z (relative intensity) 282 (M+, 14.4), 225 (14), 165 (2), 130
(9), 75 (23), 56 (100); HRMS calcd for C10H13TeF 282.0071,
found 282.0072.
Tellu r oa n isole27 (36) was prepared according to the stan-
dard protocol (E) using diphenyl ditelluride and iodomethane.
Kugelrohr distillation (35-40°/0.08 mmHg) afforded 36 as a
red oil (84%): 1H NMR δ 1.77 (3H, s), 6.87-6.99 (3H, m), 7.48-
7.55 (2H, m); 13C NMR δ 113.01, 124.70, 127.21, 129.34, 137.01;
125Te NMR δ 337.4.
1-Octyl (p h en ylselen o)for m a te (18) was prepared ac-
cording to the standard protocol (D) using diphenyl diselenide
and 1-octanol. Flash chromatography (hexane/ethyl acetate
99:1) afforded 18 as a yellow oil (70%): 1H NMR δ 0.89 (3H, t,
J ) 6.9 Hz), 1.03-1.38 (12H, m), 3.99 (2H, t, J ) 6.6 Hz), 6.98-
7.00 (3H, m), 7.58-7.61 (2H, m); 13C NMR δ 14.32, 22.99,
25.92, 28.88, 29.35, 29.42, 32.07, 68.42, 126.77, 128.98, 129.34,
136.03, 166.19; 77Se NMR δ 505.6; IR ν (CdO) (neat) 1726
cm-1; MS m/ z (relative intensity) 314 (M+, 4.2), 236 (0.9), 185
(2), 171 (0.7), 158 (100), 117 (6). Anal. Calcd for C15H22O2Se:
C, 57.51; H, 7.08. Found: C, 57.53; H, 7.26.
3â-Ch olesta n yl (p h en ylselen o)for m a te (24) was pre-
pared according to the standard protocol (D) using diphenyl
diselenide and 3â-cholestanol. Recrystallization from ethanol
afforded 24 as a white solid (72%): mp ) 138-139°; 1H NMR
δ 0.58-1.98 (46H, m), 4.89 (1H, m), 7.01-7.03 (3H, m), 7.64-
7.66 (2H, m); 13C NMR δ 12.14, 12.32, 19.02, 21.46, 22.79,
23.05, 24.36, 24.52, 27.83, 28.41, 28.64, 28.70, 32.15, 34.34,
35.40, 35.58, 36.21, 36.66, 36.76, 36.93, 40.36, 42.85, 44.54,
54.20, 56.65, 56.68, 78.70, 127.11, 128.92, 129.35, 136.00,
165.61; 77Se NMR δ 509.1; IR ν (CdO) (neat) 1719 cm-1; MS
m/ z (relative intensity) 528 (5.3), 371 (47), 316 (14), 301 (5),
203 (16), 56 (100). Anal. Calcd for C34H52O2Se: C, 71.43; H,
9.17. Found: C, 71.44; H, 8.94.
2-Meth yl-1-(p h en yltellu r o)p r op a n e28 (37) was prepared
according to the standard protocol (E) using diphenyl ditellu-
ride and 1-bromo-2-methylpropane. Ku¨gelrohr distillation
(40-50 °C/0.080 mmHg) afforded 37 as a yellow oil (70%): 1H
NMR δ 0.85 (6H, d, J ) 6.6 Hz), 1.71 (1H, m), 2.65 (2H, d, J
) 6.6 Hz), 6.88-7.03 (3H, m), 7.65-7.68 (2H, m); 13C NMR δ
20.44, 23.95, 30.19, 112.67, 127.47, 129.31, 138.54; 125Te NMR
δ 421.2; MS m/ z (relative intensity) 264 (M+, 8.4), 207 (9),
130 (8), 83 (70), 56 (100); HRMS calcd for C10H14Te 264.0165,
found 264.0157.
[(4-F lu or op h en yl)t ellu r o]cycloh exa n e (40) was pre-
pared according to the standard protocol (E) using bis(4-
fluorophenyl) ditelluride and bromocyclohexane. Ku¨gelrohr
distillation (150°/0.6 mmHg) afforded 40 as a yellow oil
(99%): 1H NMR δ 1.33 (2H, m), 1.63 (4H, m), 2.07 (4H, q, J )
10.5, 2.7 Hz), 3.43 (1H, m), 6.91 (2H, dd, J ) 9, 8.7 Hz), 7.76
(2H, dd, J ) 5.7, 8.4 Hz); 13C NMR δ 26.03, 27.25, 28.31, 29.45,
36.49, 105.56, 116.49 (d, J ) 20.3 Hz), 143.85 (d, J ) 7.6 Hz),
164.49 (d, J ) 248.3 Hz); MS m/ z (relative intensity) 308 (M+,
16.4), 226 (30), 95 (27), 83 (90), 75 (11), 55 (100); HRMS calcd
for C12H15TeF 308.0225, found 308.0211.
Sta n d a r d P r otocol (F ) for th e P r ep a r a tive-Sca le Th er -
m olysis of Alk yl (Ar yltellu r o)for m a tes. (P h en yltellu r o)-
3â-Ch olester yl (p h en ylselen o)for m a te (26) was pre-
pared according to the standard protocol (D) using diphenyl
diselenide and cholesterol. Recrystallization from ethanol
afforded 26 as a white solid (91%): mp ) 135-136°; 1H NMR
δ 0.64-2.49 (43H, m), 4.89 (1H, m), 5.25 (1H, m), 7.00-7.03
(27) McFarlane, W.; Wood, R. J . J . Chem. Soc., Dalton Trans. 1972,
1397.
(28) O’Brien, D. H.; Perev, N.; Huang, C.-K.; Irgolic, K. J . Organo-
metallics 1983, 2, 305.

(Aryltelluro)formates as Precursors of Alkyl Radicals
J . Org. Chem., Vol. 61, No. 17, 1996 5761
cycloh exa n e29 (39). Cyclohexyl (phenyltelluro)formate (19,
1.0 g, 3.02 mmol) was dissolved in benzene (1.9 mL, 1.6 M)
and heated at 160 °C for 9 d in a sealed glass vessel. Removal
of solvent in vacuo and flash chromatography (hexane) af-
forded 39 as a yellow oil (0.62 g, 71%): 1H NMR δ 1.07-2.18
(10H, m), 3.30 (1H, m), 6.92-7.04 (3H, m), 7.80-7.83 (2H, m);
13C NMR δ 26.00, 27.64, 28.25, 36.58, 112.12, 127.92, 129.24,
140.53.
(20 mL) and dried (MgSO4). Removal of the solvent in vacuo
gave an orange oil which, upon purification by flash chroma-
tography (hexane/ethyl acetate 99:1), gave the title compound
as a low-melting, white solid (598 mg, 80%): 1H NMR δ 1.16
(3H, d, J ) 6.3 Hz), 1.17-1.61 (6H, m), 2.22 (2H, t, J ) 7.2
Hz), 3.52 (2H, s), 5.38 (1H, m), 6.88-7.19 (10H, m); 13C NMR
δ 19.01, 23.58, 25.63, 27.01, 30.15, 35.03, 81.95, 122.14, 122.44,
126.37, 126.67, 126.78, 128.62, 129.20, 129.62, 129.75, 140.04,
154.00, 154.15, 195.09; 77Se NMR (CDCl3) δ 258.04; MS m/ z
(relative intensity) 260 (2.2), 258 (12), 214 (29), 141 (14), 94
(27), 91 (100). Anal. Calcd for C20H24O2SSe: C, 58.96; H, 5.94.
Found: C, 58.77; H, 6.05.
3r- a n d 3â-(P h en yltellu r o)ch olesta n e(41)25 were pre-
pared according to the standard protocol (F) using 3â-cholesta-
nyl (phenyltelluro)formate (22) in benzene (0.88 M) with
heating at 160 °C for 7 d. Removal of solvent in vacuo and
flash chromatography (hexane) afforded 41 as a mixture of
epimers (85%): 1H NMR δ 0.62-2.05 (46H, m), 3.28 (1H, m,
â isomer), 3.94 (1H, m, R isomer), 7.01 (3H, m), 7.80 (2H, d, J
) 6.9 Hz, R isomer), 7.90 (2H, d, J ) 6.0 Hz, â isomer); 125Te
δ 677.8 (R isomer), 591.4 (â isomer); MS m/ z (relative
intensity) 578 (M+, 5.55), 411 (3), 371 (30), 215 (20), 95 (84),
54 (100). Anal. Calcd for C33H52Te: C, 68.77; H, 9.09.
Found: C, 68.94; H, 8.92.
1-(Ben zylselen o)-5-h exa n ol. Sodium borohydride (1.1 g,
0.028 mol) was added to a solution of 6-bromo-2-hexanone30
(5.0 g, 0.028 mol) in dry ethanol (30 mL) under nitrogen and
the solution was left to stir for 3 h at room temperature. In a
separate reaction vessel, sodium borohydride was added to a
solution of dibenzyl diselenide (4.95 g, 0.015 mol) in dry
ethanol (200 mL) under nitrogen. After about 3 h, the solution
of the reduced ketone was transferred via cannula into the
solution containing the sodium benzylselenoate, and the
resultant mixture was stirred under nitrogen overnight at
room temperature. The solution was poured into saturated
NaHCO3 (50 mL), extracted with ether, and dried (MgSO4),
and the solvent was removed in vacuo. The residue was
subjected to flash chromatography (hexane/ethyl acetate 7:3),
and the title compound was isolated as a yellow oil (5.14 g,
68%): 1H NMR (CDCl3) δ 1.17 (3H, d, J ) 6.0 Hz), 1.38-1.65
(7H, m), 2.49 (2H, t, J ) 7.2 Hz), 3.73-3.83 (1H, m), 3.77 (2H,
s), 7.18-7.34 (5H, m); 13C NMR (CDCl3) δ 23.44, 23.88, 25.98,
26.94, 30.12, 38.62, 67.85, 126.55, 128.40, 128.75, 139.49; 77Se
NMR (CDCl3) δ 256.13; IR ν (OH stretch) 3368 cm-1. MS m/ z
(relative intensity) 272 (M+, 3.7), 108 (90), 99 (15), 79 (100),
59 (74), 45 (74). Anal. Calcd for C13H20OSe: C, 57.56; H, 7.43.
Found: C, 57.63; H, 7.50.
1-[(Tr ib u t ylst a n n yl)selen o]-5-h exyl (P h en ylt h ion o)-
for m a te (5). Tri-n-butyltin hydride (230 mg, 0.80 mmol) was
added to a solution of 1-(benzylseleno)-5-hexyl (phenylthiono)-
formate (4, 214 mg, 0.53 mmol) in benzene (20 mL, 0.03 M).
AIBN was added, and the solution was heated under nitrogen
at reflux overnight. The solvent was removed in vacuo, and
the resulting yellow oil was purified by preparative TLC
(hexane/ethyl acetate 98:2) to give the title compound as an
unstable pale oil with a distinctive pungent odor (94.1 mg,
30%): 1H NMR (CDCl3) δ 0.91 (9H, t, J ) 7.2 Hz), 1.14-1.86
(27H, m), 2.56 (2H, t, J ) 7.2 Hz), 5.38 (1H, m), 7.11 (2H, d,
J ) 8.1 Hz), 7.28 (1H, app t, J ) 6.6 Hz), 7.41 (2H, app t, J )
7.8 Hz); 13C NMR (CDCl3) δ 13.23, 13.63, 16.74, 19.03, 25.42,
27.02, 28.98, 34.20, 34.88, 82.16, 122.02, 126.36, 129.38,
153.30, 194.47; 77Se NMR (CDCl3) δ -209.78; 119Sn NMR
(CDCl3) δ 51.29; MS m/ z (relative intensity) 551 (0.4), 315 (2),
271 (10), 269 (26), 265 (11), 94 (100).
1-(Ben zylselen o)-5-h exyl (p h en yltellu r o)for m a te (44)
was prepared according to the standard protocol (B) using
1-(benzylseleno)-5-hexanol and diphenyl ditelluride. Flash
chromatography (hexane/ethyl acetate 98:2) afforded the tel-
luroformate 44 as a yellow oil (68%): 1H NMR δ 0.81-1.35
(6H, m), 0.97 (3H, d, J ) 6.0 Hz), 2.17 (2H, t, J ) 7.5 Hz),
3.51 (2H, s), 4.99 (1H, m), 6.96-7.18 (8H, m), 7.79-7.83 (2H,
m); 13C NMR δ 20.20, 23.49, 25.77, 26.94, 30.07, 35.54, 75.49,
114.21, 126.77, 128.61, 129.21, 129.54, 139.97, 140.05, 156.20;
77Se NMR δ 259.5; 125Te NMR δ 770.2; IR ν (CdO) 1708 cm-1
;
MS m/ z (relative intensity) 300 (3.7), 163 (6), 135 (1), 91 (100),
83 (3). Anal. Calcd for C20H24O2SeTe: C, 47.76; H, 4.81.
Found: C, 48.07; H, 5.17.
1,1-Dibr om o-2-m eth ylselen a n e26 (46) was prepared ac-
cording to the standard protocol (F) using 1-(benzylseleno)-5-
hexyl (phenyltelluro)formate (44, 696 mg, 1.38 mmol) and
benzene (2 mL) with heating at 160 °C for 14 d. Benzene (20
mL) was added, and the solution was distilled at atmospheric
pressure (2-methylselenane azotropes with benzene). A dilute
solution of bromine in CCl4 was added dropwise to the
distillate until the bromine color persisted. The benzene was
removed in vacuo to give the title compound 46 as a yellow/
red gum (332 mg, 74%): 1H NMR δ (CDCl3) 1.58-2.54 (6H,
m), 1.62 (3H, d, J ) 6.6 Hz), 3.85-3.89 (1H, m), 4.16 (1H, td,
J ) 4.5, 4.2, 4.5 Hz), 4.41 (1H, m); 13C NMR (CDCl3) δ 19.16,
20.24, 24.26, 29.52, 50.87, 63.88; 77Se NMR (CDCl3) δ 568.7.
1-(Ben zylselen o)-5-h exyl (P h en ylt h ion o)for m a t e (4).
Phenyl chlorothionoformate (477 mg, 2.77 mmol) and pyridine
(4.7 g, 60 mmol) were added to a solution of 1-(benzylseleno)-
5-hexanol (500 mg, 1.84 mmol) in dichloromethane (10 mL).
The solution was shielded from light while being stirred under
nitrogen overnight at room temperature. The resulting yellow
solution was poured into water (30 mL) and extracted with
ethyl acetate (2 × 25 mL). The combined organic extracts were
washed with 10% HCl (20 mL) and then saturated NaHCO3
(29) Clive, D. L. J .; Cittattu, G. L.; Farina, V.; Kiel, W. A.; Menchen,
St. M.; Russell, C. G.; Singh, A.; Wong, C. K.; Curtis, N. J . J . Am.
Chem. Soc. 1983, 102, 4438.
(30) Anderson, E. P.; Crawford, J . V.; Sherrill, M. L. J . Am. Chem.
Soc. 1946, 68, 1294.
J O960838Y