Radical sequential processes promoted by 1,5-radical translocation reaction: Formation and [3 + 2] anulation of alkenesulfanyl radicals

Article abstract of DOI:10.1021/jo960279v

Radical addition of 2-substituted ethanethiols 1-5 to alkyl-, dialkyl-, and phenylacetylenes affords the corresponding β-sulfanylalkenyl radicals, which can undergo 1,5-radical translocation (RT reaction) in competition with intermolecular hydrogen abstraction (HA reaction). The RT reaction is the first step of a sequential radical process leading to alkenesulfanyl radicals through an "intermolecular sulfanyl radical transaddition" from an alkene to an alkyne molecule. Alkenesulfanyl radicals can undergo a regioselective [3 + 2] anulation reaction with a CC triple bond, eventually leading to thiophene products through 5-endo cyclization of vinyl radicals onto CC double bond. The effect of the nature of ethanethiol and alkyne substituents on the RT/HA ratio has been investigated, and results will be discussed.

Full text of DOI:10.1021/jo960279v

J . Org. Chem. 1996, 61, 6783-6789
6783
Ra d ica l Sequ en tia l P r ocesses P r om oted by 1,5-Ra d ica l
Tr a n sloca tion Rea ction : F or m a tion a n d [3 + 2] An u la tion of
Alk en esu lfa n yl Ra d ica ls
Laura Capella, Pier Carlo Montevecchi,* and Maria Luisa Navacchia
Dipartimento di Chimica Organica “A. Mangini”, Universita` di Bologna, Viale Risorgimento 4,
I-40136 Bologna, Italy
Received February 9, 1996X
Radical addition of 2-substituted ethanethiols 1-5 to alkyl-, dialkyl-, and phenylacetylenes affords
the corresponding â-sulfanylalkenyl radicals, which can undergo 1,5-radical translocation (RT
reaction) in competition with intermolecular hydrogen abstraction (HA reaction). The RT reaction
is the first step of a sequential radical process leading to alkenesulfanyl radicals through an
“intermolecular sulfanyl radical transaddition” from an alkene to an alkyne molecule. Alkene-
sulfanyl radicals can undergo a regioselective [3 + 2] anulation reaction with a CC triple bond,
eventually leading to thiophene products through 5-endo cyclization of vinyl radicals onto CC double
bond. The effect of the nature of ethanethiol and alkyne substituents on the RT/HA ratio has been
investigated, and results will be discussed.
Sch em e 1
The 1,5-radical migration of a hydrogen atom is a well-
known reaction, but its potentiality has not been fully
explored yet. Its synthetic use is primarily confined to
the Barton reaction, involving 1,5-hydrogen shift toward
an alkoxy radical1 and to the Hofmann-Loffler reaction,2
which involves a similar 1,5-hydrogen shift toward an
aminyl radical cation.
Nevertheless, the “1,5-radical translocation” 3 easily
occurs also from alkenyl radicals, providing that a
stabilized alkyl radical can be formed. Thus, a δ-meth-
ylene having substituents capable of stabilizing the
incoming radical must be present. We will refer to this
methylene as “activated methylene” and to the stabilizing
substituents as “activating groups”. The new “translo-
cated” alkyl radicals can suitably cyclize on the alkene
double bond to form CC bonds.4,5 An extensive study on
the nature of the X and Y activating groups in radical
translocation reactions of alkenyl radicals has been
recently reported by Curran.4
During our researches on the reactivity of â-sulfanyl-
substituted alkenyl radicals,6 we have evidenced that
alkenesulfanyl radicals C can be produced from 2-(phen-
ethylsulfanyl)alkenyl radicals A by 1,5-radical translo-
cation and subsequent loss of styrene through â-scission
of resulting benzyl radicals B.6c We recognized that this
unprecedented process was worth further consideration,
generation of the previously unknown alkenesulfanyl
radicals representing a novel synthetic use of the 1,5-
radical translocation reaction.
X Abstract published in Advance ACS Abstracts, August 15, 1996.
(1) Barton, D. H. R. Pure Appl. Chem. 1968, 16, 1.
(2) Stella, L. Angew. Chem., Int. Ed. Engl. 1983, 22, 337-350.
(3) The term of “radical traslocation” has been introduced by Curran.
Radicals are generated at favorable sites and then “traslocated” to new
sites. See: Curran, D. P.; Kim, D.; Liu, H. T:; Shen, W. J . Am. Chem.
Soc. 1988, 110, 5900.
(4) Curran, D. P.; Shen, W. J . Am. Chem. Soc. 1993, 115, 6051.
(5) Gimisis, T.; Chatgilialoglu, C. J . Org. Chem, in press.
(6) (a) Benati, L.; Montevecchi, P. C; Spagnolo, P. J . Chem. Soc.,
Perkin Trans. 1 1991, 2103. (b) Benati, L.; Montevecchi, P. C.;
Spagnolo, P. J . Chem. Soc., Perkin Trans. 1 1992, 1659. (c) Benati, L.;
Capella, L.; Montevecchi, P. C.; Spagnolo, P. J . Org. Chem. 1994, 59,
2818. (d) Benati, L.; Capella, L.; Montevecchi, P. C.; Spagnolo, P. J .
Chem. Soc. Perkin Trans. 1 1995, 1035. (e) Benati, L.; Capella, L.;
Montevecchi, P. C.; Spagnolo, P. J . Org. Chem. 1995, 60, 7941.
On this basis, we have been prompted to investigate
the sequential radical process, outlined in Scheme 1,
involving formation of alkenesulfanyl radicals 26 and
their [3 + 2] anulation reaction with an alkyne triple
bond. During our study we have considered the radical
reaction of ethanethiols 1-5, carrying different activating
groups, with a number of alkynes, including alkyl-,
dialkyl, phenyl-, and phenylalkylacetylenes.
Recently, radical sequential reactions have been object
of noticeable interest, representing a useful synthetic
S0022-3263(96)00279-4 CCC: $12.00 © 1996 American Chemical Society

6784 J . Org. Chem., Vol. 61, No. 20, 1996
Capella et al.
Ta ble 1. Rela tive Yield s (%) of RT P r od u cts (28, 30, 31, a n d 36) a n d HA P r od u cts fr om Ra d ica l Ad d ition of P h en eth yl
Th iol 1 a n d 2-(Meth oxyca r bon yl)eth a n eth iol (2) to Alk yn es
entry
thiol
alkyne
hex-1-yne
tert-butylacetylene
(trimethylsilyl)acetylene
hex-3-yne
RT products
HA products
overall yield
1
2
3
4
5
6
7
8
9
1
1
1
1
1
1
1
2
2
2
2
28a (28) + 30a (3)
28b (90)
28c (90)
28d (8) + 31d (6)
28e (6) + 31e (4)
28f (6) + 30f (27)
30g (75)
28a (18) + 30a (2)
28b (60)
28d (5) + 31d (3)
28f (3) + 30f (15)
16a (69)
16b (10)
16c (10)
16d + 33 (86)
16e (90)
16f (67)
16g (25)
17a (80)
17b (40)
17d (92)
17f (82)
72
72
70
70
67
74
75
96
70
81
85
oct-4-yne
phenylacetylene
phenylpropyne
hex-1-yne
tert-butylacetylene
hex-3-yne
10
11
phenylacetylene
The best reaction conditions for obtaining the major
amounts of 28a (and 30a ) are those described under
General Procedure (see Experimental Section).
method for obtaining complex products from simple
starting molecules in a one-pot process.7
Resu lts a n d Discu ssion
According to this procedure, a benzene solution of thiol
1 was added within 4 h to a refluxing benzene solution
containing a 5-fold excess of hex-1-yne and AIBN. Under
these conditions products 28a and 16a were formed in a
ca. 30:70 ratio (see Experimental Section) (Table 1, entry
1). Comparable results were obtained by carrying out
the above reaction at 110 °C in a sealed tube (GC
analysis). Further increase in the addition time (up to
8 h) did not lead to an appreciable improvement of the
28a /16a ratio, while a decrease (0.5 h) led to a substantial
decrease in the above ratio as result of the enhancement
of the thiol concentration (with thiol being a good
hydrogen donor). Thermolysis of bis(phenethyl) disulfide
in chlorobenzene at 180 °C for 12h in the presence of hex-
1-yne led to results strictly comparable to those obtained
by generating thiyl radicals 6 from thiol 1, although
noticeable amounts of unreacted disulfide were detected
(GC analysis). On the contrary, thiyl radicals 6, when
generated from the corresponding disulfide by photolysis
with a high-pressure mercury lamp, reacted with hex-1-
yne to give unsatisfactory results. GLC analysis of the
reaction mixture showed a 5:95 RT/HA products ratio.
Poor results were also obtained by generating thiyl
radicals 6 from thiol 1 at room temperature with a 10-
fold excess of triethylborane in the presence of oxygen.
Under the conditions of General Procedure, thiols 1
and 2 were reacted with a number of alkynes. In all
cases we have examined, products deriving from the
corresponding vinyl radicals 11a-g and 12a,b,d,f through
both hydrogen abstraction (HA products 16a -g and
17a ,b,d ,f) and 1,5-radical translocation (RT products 28,
30 and 31) were observed. The relative yields of the RT
products and the HA products were found to be strongly
dependent on both the nature of R1 and R2 substituents
and the nature of the activating groups (X ) Ph or
EtOCO, Y ) H) (see Table 1).
Sulfanyl radical addition to carbon carbon triple bond
readily occurs, giving the corresponding vinyl radicals in
a reversible manner.8 The addition is strictly regiose-
lective, occurring to the terminal carbon atom with
terminal alkynes and to the alkyl-substituted carbon
atom with alkylarylacetylenes. Sulfanyl radicals can be
produced in several ways, i.e., from thiols by hydrogen
abstraction with AIBN or with the triethylborane/O2
method6e,9 or from the corresponding disulfides by ther-
mal or photochemical homolysis of the S-S bond.
Under the above conditions phenethylsulfanyl radical
6 reacted with hex-1-yne to give products 28a and 16a
in variable amounts, together with small amounts of
thiophene 30a . Vinyl sulfide 16a was derived from the
vinyl radical 11a through intermolecular hydrogen ab-
straction, while the divinyl sulfide 28a resulted from the
following sequential process: 1,5-hydrogen migration
from the activated δ-methylene affords the 1,5-translo-
cated radical 21a , which undergoes â-scission of the
carbon-sulfur bond leading to the alkenesulfanyl radical
26a with loss of stryrene. Regioselective addition of
radical 26a to an additional alkyne moleule gives the
vinyl radical 27a , from which the bis-vinyl sulfide 28a
arises by hydrogen abstraction. The small amounts of
thiophene 30a derive from radical 27a through 5-endo
cyclization onto the adiacent double bond (Scheme 1).
(7) (a) Curran, D. P. Radical addition reactions. In Comprehensive
Organic Synthesis; Pergamom Press: Oxford, U.K., 1991; Vol. 4,
Chapter 4.2. (b) Molander, G. A.; Harris, C. R. J . Am. Chem. Soc. 1995,
117, 3705.
(8) (a) Ito, O.; Omuri, R.; Matsuda, M. J . Am. Chem. Soc. 1982, 104,
3934. (b) Ito, O.; Fming, M. D. C. M. J . Chem. Soc., Perkin Trans. 2
1989, 689.
(9) Baciocchi, E.; Muraglia, E. Tetrahedron Lett. 1993, 34, 5015.
Ichinose, Y.; Wakamatsu, K.; Nazaki, K.; Birbaum, J -L; Oshima, K.;
Utimoto, K. Chem. Lett. 1987, 1647.
(10) Curran, D. P. Radical addition reactions. In Comprehensive
Organic Synthesis; Pergamon Press: Oxford, U.K., 1991; Vol. 4,
Chapter 4.1.4.3. Giese, B. Angew. Chem., Int. Ed. Engl. 1983, 22, 753.
(11) (a) Stork, G.; Mook, R., J r. J . Am. Chem. Soc. 1987, 109, 2829.
(b) Stork, G.; Baine, N. H. J . Am. Chem. Soc. 1982, 104, 2321. (c) Stork,
G.; Baine, N. H. Tetrahedron Lett. 1985, 26, 5927. (d) Capella, L.;
Montevecchi, P. C.; Navacchia, M. L. J . Org. Chem. 1995, 60, 7424.
(12) Baldwin, J . E. J . Chem. Soc., Chem. Commun. 1976, 734.
Beckwith, A. L. J .; Easton, C. J .; Serelis, A. K. J . Chem. Soc., Chem.
Commun. 1980, 482.
The dependence of the RT product/HA product ratio
on the R1 and R2 substituent nature is probably due to
steric effects. For example, the linear R-phenylalkenyl
radicals 11f and 11g (Table 1, entries 6 and 7) afforded
RT products in a different extent. The effect of the
â-methyl substituent in increasing the RT product/HA
product ratio could be related to the increased steric
hindrance to the approach of the radical scavenger by
increasing the size of the â-substituent.14
(13) Giese, B. Angew. Chem., Int. Ed. Engl. 1989, 28, 969. Giese, B;
Lachein, S., Angew. Chem., Int. Ed. Engl. 1982, 21, 768. Singer, L. A.;
Chen, J ., Tetrahedron Lett. 1969, 4849.
(14) It is generally accepted that steric hindrance between radical
scavenger and the substituent cis to the radical center is an important
effect in determining the stereochemistry of radical addition of thiols
to alkynes (refs 6a,d; see also: Chatgilialoglu, C.; Ferreri, C. Free
Radical Addition involving C-C triple bonds. In The Chemistry of
Triple-bonded Functional Groups; Patai, S., Ed.; J . Wiley: New York,
1994; Suppl. C2, Vol. 2, Chapter 16.

1,5-Radical Translocation Reaction
J . Org. Chem., Vol. 61, No. 20, 1996 6785
Ta ble 2. P r od u cts (Rela tive Yield s, %) fr om Rea ction s of
P h en yla cetylen e w ith Eth a n eth iols 1-5 a n d Th iola cetic
Acid (38)
Sch em e 3
products, relative yields (%)
1:1
RT/HA overall
entry thiol
28f
30f
adduct
34
ratio
yield
1
2
3
4
5
6
1
2
3
4
5
5
2
24
13
56
7
45
0
(16f) 59 12
(17f) 69 16
33:67
18:82
100:0
8:92
60:40
0:100
82
98
67
65
75
36
18
traces
8
0
(18f) 0
19
(19f) 79 14
(20f) 36 10
38
(40) 60
40
Sch em e 2
Similarly, radicals 11b and 11c (which are in turn
believed to be sp-linear6b,15) gave a high RT product/HA
product ratio, probably as a result of the steric hindrance
between the bulky R-substituent and the radical scav-
enger (Table 1, entries 2 and 3).
that of thiol 2, in spite of the fact that a tert-alkyl radical
is less stable than a benzylic radical.
R,â-Dialkyl-substituted radicals 11d and 11e (Table 1,
entries 4 and 5) gave instead predominant formation of
HA products over RT products. It can likely be inferred
that steric hindrance between the alkyl substituents R1
and R2 shifts the equilibrium between E- and Z-inter-
converting isomers toward the Z-configuration, which is
not suitable for the RT reaction.16 Reaction of thiol 1 with
hex-3-yne gave a regioisomeric mixture of (E)- and (Z)-
16d and (E)- and (Z)-33. We found that the 16d /33 ratio
considerably changed when the isomeric mixture was
allowed to stand at room temperature for several days
in the presence of small amounts of thiol 1. In this light,
adduct 33 can be considered as deriving from 16d
through a postisomerization process, possibly involving
reversible addition of thiol to the carbon-carbon double
bond (Scheme 2).17
In principle, the effect of the X-activating groups (X )
Ph or EtOCO) in determining the RT product/HA product
ratio should be related to the different stability of the
resulting translocated radicals 21 and 22. The effect the
activating groups is more evident by comparison of
results collected in Table 2, showing the RT products/
HA products ratios from reactions of ethanethiols 1-5
with phenylacetylene carried out under the conditions
of General Procedure. An increase in the stability of the
translocated radical generally favors the 1,5-radical
translocation over the hydrogen abstraction reaction. In
particular, no hydrogen abstraction product 18f was
formed from 2,2-diphenylethanethiol (3), having two
phenyl substituents as activating groups. However, it
would appear that the stability of the new translocated
radicals cannot be the only determining factor. In fact,
thiol 5 gave a RT products/HA products ratio higher than
The entire process, leading to alkenesulfanyl radicals
26 from alkanesulfanyl radicals 6-10, can be envisaged
as a formal “intermolecular sulfanyl radical transaddi-
tion” from an alkene toward an alkyne molecule. The
driving force should be the higher stability of radicals
21-25 with respect to 11-15.
It is noteworthy that â-scission is the exclusive reaction
exhibited by radical intermediates 21-25. Indeed, â-cleav-
age of the carbon-sulfur bond of â-sulfanyl-substituted
alkyl radicals is a fast reaction.10 In agreement, no
products deriving from radicals 21-25 through 5-endo
cyclization on the adjacent double bond were formed in
all the examined cases. Moreover, we ruled out the
possibility that radicals 21-25 undergo a competing
hydrogen abstraction reaction leading to adducts 16-20
by reacting S-deuterated thiol 1 with phenylacetylene.
The resulting adduct 16f was found to be deuterated at
the R-vinylic position (ca. 70:30 D/H ratio) (Scheme 3),
whereas no deuterium was incorporated at the benzylic
position (1H NMR analysis).
As outlined above, alkenesulfanyl radicals 26 undergo
regioselective addition to the alkyne triple bond leading
to vinyl radicals 27. However, competing side reactions
can occur under the reaction conditions employed For
example, products 32a ,b,d , deriving from trapping of
26a ,b,d by 2-cyanopropyl radicals, have been evidenced
(Scheme 1).
(15) Griller, D.; Cooper, J . W.; Ingold, K. U. J . Am. Chem. Soc. 1975,
97, 4269.
Radicals 27 undergo 5-endo cyclization onto the adja-
cent double bond, eventually leading to thiophene deriva-
tives 30 and 31, in competition with the hydrogen
abstraction reaction leading to bis-vinyl sulfides 28.
Products 28 are generally obtained as (E,E)- and (E,Z)-
isomeric mixtures. Reaction of thiol 1 with phenylacety-
lene led to alkenyl sulfides 28f in a ca. 90:10 (E,Z)/(Z,Z)
ratio. 1H NMR analysis of sulfides 28f obtained from the
(16) Dialkylacetylenes undergo radical addition of benzenethiol
leading to (Z) and (E)-adducts in a Z/E ratio increasing with the size
of alkyl substituents (refs 6a,e). The predominant formation of trans-
addition (Z)-products with hex-3-yne and oct-4-yne would result from
predominant occurrence of (Z)-radicals in the mixture of equilibrating
(Z)- and (E)-radicals, owing to steric hindrance between the alkyl
substituents.
(17) Reversible radical addition of thiols to alkenyl sulfides leading
to dithioacetals has been reported (Oswald, A. S.; Griesbaum, K.;
Hudson, B. E.; Bregman, J . M. J . Am. Chem. Soc. 1964, 86, 2877).

6786 J . Org. Chem., Vol. 61, No. 20, 1996
Capella et al.
Sch em e 4
reaction of S-deuterated thiol 1 showed that the (E,Z)-
isomer had incorporated deuterium in the position trans
to the sulfur atom (D/H ca. 65:35). According to reaction
mechanism (Scheme 3), it can be inferred that trans-
alkenylthio radicals 26f are formed from 21f. Moreover,
according to the general evidence for radical addition of
thiols to phenylacetylenes,6a,d R-phenyl-substituted radi-
cal 27f mainly undergoes hydrogen abstraction from the
side trans to the sulfur atom (Scheme 3).
The 5-endo cyclization of alkenyl radicals onto the CC
double bond is considered a stereoelectronically disfa-
vored process. Actually, these reactions are quite rare,
although examples have been reported.11
Competition between the 5-endo cyclization and the
hydrogen abstraction reaction is strongly affected by the
nature of R1 and R2 substituents, as evidenced from
results obtained by reacting thiols 1 and 2 with a number
of different alkynes (Table 1). With hex-1-yne (Table 1,
entry 1, 8) sulfide 28a was the main RT product, in
addition to very small amounts of the thiophene deriva-
tive 30a . The poor tendency of 27a to undergo 5-endo
cyclization on the alkene double bond parallels the
behavior encountered with related â-(phenylsulfanyl)-R-
alkyl-substituted vinyl radicals 34, R1 ) H, R2 ) alkyl,
which were found not to undergo ortho cyclization onto
the phenyl ring (similar to a 5-endo cyclization) even at
very high reaction temperature.6b However, when a
further alkyl substituent is present in the â-position
(Table 1, entries 4, 5, and 10), alkenyl radicals 27d ,e
showed a greater propensity to undergo 5-endo cycliza-
tion. The effect of the â-alkyl substituent (previously
observed6b in related cyclizations on the phenyl ring of
radicals 34, R1 ) R2 ) alkyl) is unclear.
20f and the RT products 28f, 30f, and 31f, 2,4-diphen-
ylthiophene 36 (Table 2). In principle, thiophene 36
might have been derived from the alkenesulfanyl radical
26f, which can exist in the mesomeric form 26′f and be
considered an ambident radical. Thus, thiophene 36
could arise by addition of the carbon-centered radical 26′f
to phenylacetylene and subsequent ring closure of the
resulting vinyl radical 35 by intramolecular addition to
the carbon-sulfur double bond (Scheme 4, path a).
However, another route is opened for thiophene 36, which
could result from radicals 11f-15f through initial addi-
tion to a further molecule of phenylacetylene (Scheme 4,
path b). Resulting vinyl radicals 37 could give thiophene
36 by SH2 reaction at sulfur, with displacement of a
2-substituted ethyl radical. A similar behavior has been
previously encountered in radical addition of thiopheneth-
iol to phenylacetylene.6e
Both proposed mechanisms involve initial carbon-
centered radical addition to phenylacetylene. However,
the route involving radical 26′f does not appears to be
conceivable in our opinion. In fact, the ratio of addition
products to phenylacetylene by the sulfur-centered radi-
cal 26 (RT products 28f and 30f) and by the carbon-
centered radical 26′f (thiophene 36) cannot depend on
the reaction conditions, including the nature of the thiol
1-5. Vice versa, we can observe from Table 2 that the
(28f + 30f)/36 ratio strongly depends on the nature of
the thiol 1-5 employed. This finding is instead in
agreement with the route involving radical 11f-15f
addition to phenylacetylene. This reaction should com-
pete with both hydrogen abstraction and radical trans-
location, and it is expected to be strongly influenced by
the nature of the thiol employed. Compelling evidence
came from reaction of thiolacetic acid (38) with pheny-
lacetylene. Reaction of thiol 38 with hex-1-yne has been
previously reported to give only the thiol/alkyne adduct.18
In contrast, we found that thiol 38 reacted with phenyl-
acetylene to give comparable amounts of 1:1 adduct 40
and thiophene 36, although in somewhat low overall
yields (Scheme 5 and Table 2, entry 6). No thiophene
derivative 30f, or bis-vinyl sulfide 28f, or other products
possibly deriving from 1,5-radical translocation could be
detected.
The marked R-phenyl effect in promoting 5-endo cy-
clization can be explained according to Baldwin-Beck-
with’s rules for radical cyclizations.12 The transition state
for a 5-endo-trig cyclization is achieved when the un-
paired electron containing orbital and the CC double bond
form an angle of 109°. This situation is better achieved
for R-phenyl linear sp-hybridized vinyl radicals 27f,g,9a,13
having the unpaired electron in the p-orbital, rather than
for R-alkyl bent vinyl radicals 27a ,d ,e, having the un-
paired electron in the sp2-orbital.
A remarkable effect in promoting 5-ortho cyclization
onto the phenyl ring had been also provided by radicals
34 having bulky R-substituents, such as tert-butyl and
trimethylsilyl groups.6b In contrast with this early
evidence, no 5-endo cyclization products were obtained
from radicals 27b,c (Table 1, entries 2, 3, and 9). We
suggest that steric hindrance between the bulky substit-
uents inhibits radicals 27b ,c from reaching the cisoid
conformation suitable for cyclization.
Finally, attempts to trap radicals 26 by addition on
alkene double bonds failed. Reaction of thiol 2 with
phenylacetylene carried out in the presence of a 10-fold
excess of cyclohexene or methyl acrylate did not lead to
any product deriving from radical addition of 26f to the
carbon-carbon double bond. The product patterns of the
above reactions were identical to those obtained from the
same reaction carried out in the absence of any alkene
(GC, GC-MS, and TLC analyses). Indeed, the failure to
In all cases we have examined, reaction of thiols 1-5
with phenylacetylene gave, besides the HA products 16-
(18) Kampmeier, J . A.; Chen, G. J . Am. Chem. Soc. 1975, 87, 2608.

1,5-Radical Translocation Reaction
J . Org. Chem., Vol. 61, No. 20, 1996 6787
Further portions of AIBN (55 mg) were added after 1.5 and 3
h. The reaction mixture was refluxed for a further 1 h;
afterward the solvent was removed and the residue was
analyzed by GC/MS and then chromatographed.
Sch em e 5
Rea ction s of Th iols 1-5 w ith P h en yla cetylen e. Elution
with light petroleum ether gave, besides the products described
below, 1,3,5-triphenylbenzene24 (ca. 20-30 mg); elution with
light petroleum ether/diethyl ether 95:5 gave a mixture of
products probably deriving from addition of 2-cyanopropyl
radicals to phenylacetylene (ca. 50-60 mg).24 Further elution
with light petroleum ether/diethyl ether 90:10 gave noticeable
amounts (yield not determined) of complex mixtures of uni-
dentifiable products.
F r om P h en eth yl Th iol 1. Chromatography gave 2,4-
diphenylthiophene (36) (47 mg, 10%), 3,4-diphenyl-2,3-dihy-
drothiophene (30f) (95 mg, 20%), dialkenyl sulfide 28f (20 mg,
4%) [ca. 15:85 (E,E)/(E,Z) mixture], and a ca. 80:20 (Z)/(E)
mixture of (Z)- and (E)-adduct 16f (230 mg, 48%). A benzene
solution of 30f was refluxed for 30 min in the presence of 1.5
molar equiv of DDQ; the reaction was filtered on a silica gel
column (h ) 10 cm) and the solvent distilled off to yield 3,4-
diphenylthiophene (31f) (ca. 100%).
give addition products would not result from the inca-
pability of radical 26f of adding to alkenes. In this
respect, radical 26f would show a behavior similar to that
generally exhibited by other sulfanyl radicals, which are
known to undergo rapid and reversible addition on the
carbon-carbon double bond.10
Con clu sion s
The reaction was repeated by using S-deuterated phenethyl
thiol (90:10 D/H ratio), which was prepared by shaking a
benzene solution (5 mL) of 1 (2 mmol) with D2O (0.5 mL).
Chromatography allowed for separation of a fraction contain-
ing a 30:70 mixture of (Z)-16f and (Z)-R-deuterio-â-styrylphen-
ethyl sulfide [1-deuterio-(Z)-16f] [1H NMR δ (200 MHz) 3.0
(4H, m), 6.26 (0.7 H, br s, line width ca. 3.5 Hz), 6.26 (0.3 H,
A part of an AB system, J ) 10.8 Hz), 6.48 (0.3 H, B part of
an AB system, J ) 10.8 Hz), 7.2-7.5 (10H, m)] and an ca.
15:85 mixture of (E,E)-28f and (Z)-R-deuterio-â-styryl (E)-â-
styryl sulfide (1-deuterio-(E,Z)-28f) (D/H ratio ca. 65:35) [1H
NMR δ (200 MHz) 6.49 (0.65 H, br s, line width ca. 3,5 Hz),
6.49 (0.35 H, A part of an AB system, J ) 11 Hz), 6.62 (0.35
H, B part of an AB system, J ) 11 Hz), 6.7 (1H, A′ part of an
A′B′ system, J ) 15 Hz), 6.85 (1H, B′ part of an A′B′ system,
J ) 15 Hz), 7.2-7.6 (aromatic protons)].
The overall findings show that alkenesulfanyl radicals
26 can be smoothly generated by radical addition of
ethanethiols carrying 2-activating groups to alkynes
through transaddition of a sulfanyl radical moiety from
an alkene to an alkyne molecule. This process is pro-
moted by an initial 1,5-radical translocation from an
alkenyl to an alkyl position. Alkenesulfanyl radicals 26
add to CC triple bond in a regioselective fashion; however,
the subsequent 5-endo cyclization of resulting alkenyl
radicals 27 on the adjacent double bond occurs in a
satisfactory manner only with linear sp-hybridized R-
phenyl radicals.
Exp er im en ta l Section
F r om 2-(Eth oxyca r bon yl)eth a n eth iol 2. Chromatogra-
phy gave thiophene 36 (75 mg, 16%), dihydrothiophene 30f
(60 mg, 13%), dialkenyl sulfide 28f (10 mg, 2%), and a 90:10
(Z)/(E) mixture of 2-(ethoxycarbonyl)ethyl â-styryl sulfide (17f)
(320 mg, 69%) [1H NMR δ (200 MHz) 1.27 (3H, t, J ) 7.5 Hz),
2.7 (2H, t, J ) 7.0 Hz), 3.07 (2H, t, J ) 7.0 Hz), 4.15 (2H, q, J
) 7.5 Hz), 6.24 (0.9H, A part on AB system, J ) 10.6 Hz), 6.4
(0.1H, A′ part of an A′B′ system, J ) 15 Hz,), 6.48 (0.9H, B
part of an AB system, J ) 10.6 Hz), 6.62 (0.1H, B′ part of an
A′B′system, J ) 15 Hz), 7.2-7.5 (5H, m); MS m/z (rel intensity)
Thiols 1, 2, 4, 5, and 38 and all the alkynes employed were
commercially available. Thiol 3 was prepared according to
Volante’s method19 in 30% yield and was reacted without
further purification. [1H NMR δ (200 MHz) 1.35 (1H, t, J )
7.5 Hz; collapsing to singlet upon irradiation at δ 3.20), 3.20
(2H, t, J ) 7.5 Hz), 4.15 (1H, t, J ) 7.5 Hz; collapsing to singlet
upon irradiation at δ 3.20), 7.15-7.35 (10H, m); MS m/z (rel
intensity) 214 (M+, 10), 167 (100), 165 (50), 152 (30); HRMS
calcd for C14H14S 214.08162, found 214.08153.]
236 (M+, 100), 135 (70), 134 (20), 91 (60). Anal. Calcd for C13
-
Adducts 16a 6c and 16f,6c dialkenyl sulfides 28a 6c and 28f,6c
and thiophene derivatives 30f,20 31f,21 and 36,21,22 were identi-
fied by GC-MS spectral comparison with authentic specimens.
Structural assignment to the new reaction products generally
arose from 1H NMR and MS spectral data in addition to
elemental analysis. Adducts 16a -g, 17a ,b,d ,f, 19f, 20f, and
dialkenyl sulfides 28a -f were separated as E/Z mixtures.
Compounds 16g, 28d , and 28e were not isolated as pure
products. Mixtures with the corresponding thiophene deriva-
tives 30g, 31d ,22 and 31e,23 respectively, were obtained. Their
identification arose by careful GC-MS and 1H NMR spectral
analysis in addition to HRMS. Column chromatography was
performed on Merck silica gel (0.040-0.063 particle size) by
gradual elution with light petroleum ether (bp 40-70 °C)-
diethyl ether.
H16O2S: C, 66.07; H, 6.82; O, 13.54, S, 13.57. Found: C, 66.40;
H, 6.80; S, 13.65]
F r om 2,2-Dip h en yleth a n eth iol (3). Chromatography
gave diphenylethylene (yield not determined), thiophene 36
(60 mg, 13%), dihydrothiophene 30f (175 mg, 38%), and
dialkenyl sulfide 28f (55 mg, 12%).
F r om n -Dod ecyl Th iol 4. Chromatography gave 2,4-
diphenylthiophene (36) (42 mg, 9%), dihydrothiophene 30f (20
mg, 4.5%), and a 80:20 (Z)/(E) mixture of n-dodecyl â-styryl
sulfide (19f) (300 mg, 50%) [1H NMR δ (200MHz) 0.8-0.9 (3H,
m), 1.1-1.4 (18H, m), 1.55-1.75 (2H, m), 2.65-2.8 (2H, m),
6.24 (0.8H, A part of an AB system, J ) 11 Hz), 6.43 (0.8H, B
part of an AB system, J ) 11 Hz), 6.45 (0.2H, A′ part of an
A′B′ system, J ) 15 Hz), 6.72 (0.2H, B′ part of an A′B′ system,
J ) 15 Hz), 7.15-7.5 (5H, m); MS m/z (rel intensity) 304 (M+,
90), 136 (100), 135 (95). Anal. Calcd for C20H32S: C, 78.88;
H, 10.59; S, 10.53. Found: C, 79.20; H, 10.65; S, 10.48].
Traces amounts of dialkenyl sulfide 28f were detected by GC/
MS.
Rea ction s of Th iols 1-5 a n d 38 w ith Alk yn es. Gen er a l
P r oced u r e. A benzene solution (10 mL) of the appropriate
thiol 1-5 and 38 (2 mmol) in boiling benzene (40 mL) was
added within 4 h with a syringe pump to a solution of the
appropriate alkyne (10 mmol) and AIBN (55 mg, 0.33 mmol).
F r om 2-Meth ylp r op a n eth iol (5). Chromatography gave
2,4-diphenylthiophene (36) (35 mg, 7.5%), dihydrothiophene
30f (160 mg, 34%), a ca. 80:20 (Z)/(E) mixture of 2-methylpro-
pyl â-styryl sulfide (20f) (100 mg, 27%) [1H NMR δ (200 MHz)
1.02 (4.8H, d, J ) 7.5 Hz), 1.03 (1.2H, d, J ) 7.5 Hz), 1.8-2.0
(19) Volante, R. P. Tetrahedron Lett. 1981, 22, 3119.
(20) Block, E.; Corey, E. J . Org. Chem. 1969, 34, 896.
(21) Wymberg, H.; VanDriel, H.; Kellogg, R. M.; Buter, J . J . Am.
Chem. Soc. 1967, 89, 3487.
(22) Belen’kh, L. I.; Yakubov, A. P. Tetrahedron 1986, 42, 759.
(23) Dzhemilev, U. M.; Baibulatova, N. Z.; Tkatchenko, T. K.;
Kunakova, R. V.; Khalilov, L. M.; Berg, A. A. Izv. Akad. Nauk. SSSR,
Ser. Khim. 1989, 655; Chem. Abstr. 1989, 111, 232699y.
(24) The source of these products is still unclear. A study of carbon-
centered radical addition to the alkyne triple bond is in progress.

6788 J . Org. Chem., Vol. 61, No. 20, 1996
Capella et al.
(1H, m), 2.70 (2H, d, J ) 7.5 Hz), 6.24 (0.8H, A part of an AB
system, J ) 11 Hz), 6.41 (0.8H, B part of an AB system, J )
11 Hz), 6.47 (0.2H, A′ part of an A′B′ system, J ) 15 Hz), 6.73
(0.2H, B′ part of an A′B′ system, J ) 15 Hz), 7.2-7.5 (5H, m);
MS m/z (rel intensity) 192 (M+, 60), 136 (80), 135 (100). Anal.
Calcd for C12H16S: C, 74.94, H, 8.39, S, 16.67. Found: C,
74.65; H, 8.43; S, 16.60], and dialkenyl sulfide 28f (35 mg, 6%).
Rea ction of Th iola cetic Acid (38) w ith P h en yla cety-
len e. Elution with light petroleum ether gave 2,4-diphenyl-
thiophene (36) (68 mg, 14%) and a (Z)-adduct, (Z)-40 (75 mg,
21%) [1H NMR δ (200 MHz) 2.45 (3H, s), 6.72 (1H, d, J ) 10.7
Hz), 6.93 (1H, d, J ) 10.7 Hz), 7.2-7.4 (5H, m); MS m/z (rel
intensity) 178 (M+, 30), 136 (100), 135 (90), 91 (30). Anal.
Calcd for C10H10OS: C, 67.38, H, 5.65, O, 8.98; S, 17.99.
Found: C, 67.70; H, 5.68; S, 17.90]. Further elution with light
petroleum-diethyl ether 90:10 gave complex mixtures of
unidentifiable products.
(2H, q, J ) 7.5 Hz), 5.7 (0.15H, A part of an AB system, J )
10.2 Hz), 5.71 (0.15H, B part of an AB system, J ) 10.2 Hz),
5.73 (0.85H, A′ part of an A′B′ system, J ) 15.3 Hz), 5.82
(0.85H, B′ part of an A′B′ system, J ) 15.3 Hz); MS m/z (rel
intensity) 216 (M+, 50), 201 (90), 115 (50), 113 (50), 101 (40),
99 (90), 83 (100). Anal. Calcd for C11H20O2S: C, 61.07; H,
9.32, O, 14.79, S, 14.82. Found: C, 61.30; H, 9.37; S, 14.75].
Further elution with light petroleum ether/diethyl ether 90:
10 gave complex mixtures of unidentifiable products.
Rea ction of Th iols 1 a n d 2 w ith Hex-3-yn e. F r om
P h en eth yl Th iol 1. Chromatography gave a 3:2 mixture of
bis(hex-3-en-1-yl) sulfide (28d ) [(E,E), (Z,Z), and (E,Z) isomeric
mixture] and tetraethylthiophene 31d (40 mg, 10% overall
yield) [28d : 1H NMR δ (200 MHz) 1.0 (6H, m), 2.0-2.2 (2H,
m, allylic methylenes), 2.2-2.35 (2H, m, allylic methylenes),
5.4-5.8 (2H, vinylic protons). Triplets at δ 5.48 (J ) 7.5 Hz,
collapsing to singlet upon irradiation at δ 2.1), 5.59 (J ) 7.5
Hz, collapsing to singlet upon irradiation at δ 2.1), 5.68 (J )
6.0 Hz, collapsing to singlet upon irradiation at δ 2.3), and
5.75 (J ) 6.0 Hz, collapsing to singlet at δ 2.3); GC/MS m/z
(rel intensity) 198 (M+, 50), 169 (100), 155 (40); HRMS calcd
for C12H22S 198.14422; found 198.14447. 31d : 1H NMR δ (200
MHz) 1.08 (3H, t, J ) 7.5 Hz), 1.28 (3h, t, J ) 7.5 Hz), 2.47
(2H, q, J ) 7.5 Hz, collapsing to singlet upon irradiation at δ
1.08), and 2.72 (2H, q, J ) 7.5 Hz, collpasing to singlet upon
irradiation at δ 1.28); GC/MS m/z (rel intensity) 196 (M+, 30),
181 (100)] and a mixture of (E)- and (Z)-hex-3-en-1-yl phen-
ethyl sulfide (16d ) and (E)- and (Z)-hex-2-en-3-yl phenethyl
sulfide (33) (260 mg, 60%). Repeated column chromatography
allowed for separation of fractions containing almost pure (E)-
16d and (Z)-16d [1H NMR δ (300 MHz) [(E)-16d ] 0.98 (3H, t,
J ) 7 Hz), 1.1 (3H, t, J ) 7 Hz), 2.25 (4H, m), 2.80 (4H, m),
5.65 (1H, t, J ) 6.7 Hz, collapsing to singlet upon irradiation
at δ 2.25), 7.15-7.35 (5H, m); δ (300 MHz) [(Z)-16d ] 1.0 (3H,
t, J ) 7.0 Hz), 1.1 (3H, t, J ) 7.0 Hz), 2.10 (2H, quintuplet, J
) 7.0 Hz, collapsing to quartet upon irradiation at δ 5.38),
2.22 (2H, q, J ) 7.0 Hz), 2.85 (4H, m), 5.38 (1H, t, J ) 7.0
Hz), 7.15-7.35 (5H, m); MS m/z (rel intensity) 220 (M+, 60),
116 (80), 115 (80), 105 (100). Anal. Calcd for C14H20S: C,
76.30; H, 9.15; S, 14.55. Found: C, 76.60; H, 9.20; S, 14.48].
A benzene solution of the (E)- and (Z)-16d mixture was allowed
to stand at room temperature for 3 days in the presence of
thiol 1 (ca. 0.2 molar equiv). 1H NMR analysis showed
formation of a ca. 1:1:1:1 mixture of (E)- and (Z)-16d and (E)-
and (Z)-33 [(E)- and (Z)-33: 1H NMR δ (300 MHz) 0.9-1.0 (6H,
m), 1.5-1.65 (4H, m), 1.72 (3H, d, J ) 7.0 Hz), 1.82 (3H, dt,
J d ) 6.7 Hz, J t ) 1.0 Hz), 2.15-2.30 (4H, m), 2.8-2.9 (4H, m),
5.54 (1H, q, J ) 7.0 Hz, collapsing to singlet upon irradiation
at δ 1.72), 5.74 (1H, qt, J q ) 6.7 Hz, J t ) 1.0 Hz, collapsing to
triplet, J ) 1.0 Hz, upon irradiation at δ 1.82, collapsing to
quartet upon irradiation at δ 2.2), 7.15-7.4 (10H, m)]. GC/
MS of the reaction mixture showed the presence of possible
adduct 32d [MS m/z (rel intensity) 183 (M+, 10), 154 (40), 115
(15), 73 (100)].
F r om 2-(Eth oxyca r bon yl)eth a n eth iol (2). Chromatog-
raphy gave a 3:2 miture of bis(hex-3-en-1-yl) sulfide (28d ) and
tetraethylthiophene 31d (25 mg, 6%) and a 55:45 (Z)/(E)
mixture of 2-(ethoxycarbonyl)ethyl hex-3-en-1-yl sulfide (17d )
(320 mg, 73%) [1H NMR δ (200 MHz) 0.9-1.15 (6H, m), 1.27
(3H, t, J ) 7.5 Hz), 2.0-2.3 (4H, m), 2.45-2.65 (2H, m), 2.8-
2.95 (2H, m), 4.15 (2H, q, J ) 7.5 Hz), 5.40 (0.55H, t, J ) 7.0
Hz), 5.67 (0.45H, br t, J ) 7.0 Hz); MS m/z (rel intensity) 216
(M+, 30), 115(100). Anal. Calcd for C11H20O2S: C, 61.07; H,
9.32; O, 14.79; S, 14.82. Found: C, 60.90; H, 9.35; S, 14.90].
Rea ction of P h en eth yl Th iol 1 w ith (Tr im eth ylsilyl)-
a cetylen e. Elution with light petroleum ether gave a ca. 90:
10 (E,E) and (E,Z) mixture of bis(trimethylsilyl)vinyl sulfide
(28c) (275 mg, 60%) [1H NMR δ (200 MHz) [(E,E)-28c] 0.10
(9H, s), 6.0 (1H, d, J ) 17.8 Hz) and 6.65 (1H, d, J ) 17.8 Hz);
(E,Z)-28c showed vinylic protons at δ 5.8 (d, J ) 13 Hz), 7.05
(J ) 13 Hz), 5.89 (d, J ) 17.8 Hz), and 6.57 (17.8 Hz); MS m/z
(rel intensity) 230 (M+, 20), 127 (50), 73 (100). Anal. Calcd
for C10H22SSi2: C, 52.10; H, 9.62; S, 13.91; Si, 24.37. Found:
C, 52.26; H, 9.65; S, 13.85] and (E)-trimethylsilyl phenethyl
sulfide (16c) (45 mg, 10%) [1H NMR δ (200 MHz) 0.10 (9H, s),
2.9-3.0 (4H, m), 5.85 (1H, d, J ) 18 Hz), 6.50 (1H,d, J ) 18
Rea ction s of Th iols 1-2 w ith Hex-1-yn e. F r om P h en -
eth yl Th iol 1. Chromatography gave a mixture of (E,E)- and
(E,Z)-bis(hex-1-en-1-yl) sulfide 28a (80 mg, 20%), 3,4-dibutyl-
2,3-dihydrothiophene (30a ) (10 mg, 2%) [1H NMR δ (200 MHz)
0.9 (6H, m), 1.2-1.5 (10H, m), 2.0-2.2 (2H, m; allylic meth-
ylene), 2.7-2.85 (1H, m), 2.92 (1H, ABX system, J AX ) 10.5
Hz; J AB ) 6.0 Hz), 3.35 (1H, dd, J 1 10.5 Hz, J 2 ) 8.5 Hz), 5.65
(1H, br s); MS m/z (rel intensity) 198 (M+, 50), 141 (100);
HRMS calcd for C12H22S 198.14422, found 198.14445], and a
ca. 1:1 (E)/(Z) mixture of phenethyl hex-1-en-1-yl sulfide (16a )
(220 mg, 50%). GC/MS analysis of the reaction mixture
showed the presence of possible adduct 32a [MS m/z (rel
intensity) 183 (M+, 30), 140 (40), 126 (50), 115 (20), 73 (100)].
F r om 2-(Eth oxyca r bon yl)eth a n eth iol (2). Chromatog-
raphy gave bis(hexenyl) sulfide 28a (65 mg, 17%), dihy-
drothiophene 30a (10 mg, 2%), and a 50:50 (Z)/(E) mixture of
2-(ethoxycarbonyl)ethyl hex-1-en-1-yl sulfide (17a ) (335 mg,
78%) [1H NMR δ (200 MHz) 0.8-0.95 (3H, m), 1.25-1.45 (4H,
m), 1.27 (3H, t, J ) 7.5 Hz), 2.0-2.2 (2H, m), 2.62 (2H, t, J )
7.0 Hz), 2.85-2.95 (2H, m), 4.15 (2H, q, J ) 7.5 Hz), 5.62 (0.5H,
A part of an ABX2 system, J AB ) 9 Hz, J AX ) 6.8 Hz), 5.72
(0.5H, A′ part of an A′B′X′2 system, J A′B′ ) 15 Hz, J A′X′ ) 6.8
Hz), 5.88 (0.5H, B part of an ABX2 system, J AB ) 9 Hz, J AX
)
1.4 Hz), 5.88 (0.5H, B′ part of an A′B′X′2 system, J A′B′ ) 15
Hz, J B′X′ ) 1.0 Hz); MS m/z (rel intensity) 216 (M+, 50), 173
(30), 115 (70), 85 (100), 82 (70), 73 (90). Anal. Calcd for
C11H20O2S: C, 61.07; H, 9.32; O, 14.79, S, 14.82. Found: C,
60.90; H, 9.37; S, 14.75].
Rea ction of Th iols 1 a n d 2 w ith 3,3-Dim eth ylbu t-1-yn e.
F r om P h en eth yl Th iol 1. Elution with light petroleum ether
gave a 97:3 (E,E)/(E,Z) mixture of bis(3,3-dimethylbut-1-en-
1-yl) sulfide (28b) (260 mg, 65%) [1H NMR δ (200 MHz) 1.05
(9H, s), 5.75 (1H, A part of an AB system, J ) 15 Hz), 5.90
(1H, B part of an AB system); low-intensity doublets are
present at δ 5.52 (J ) 11Hz) and 5.87 (J ) 15 Hz); MS m/z
(rel intensity) 198 (M+, 20), 183 (20), 57 (100). Anal. Calcd
for C12H22S: C, 72.66; H, 11.18; S, 16.16. Found: C, 72.37; H,
11.24; S, 16.23] and a ca. 95:5 (E)/(Z) mixture of 3,3-dimeth-
ylbut-1-en-1-yl phenethyl sulfide (16b) (30 mg, 7%) [1H NMR
δ (E)-isomer [200 MHz] 1.05 (9H, s), 2.95 (4H, br s), 5.7 (1H,
A part of an AB system, J ) 15 Hz), 5.85 (1H, B part of an AB
system, J ) 15 Hz), 7.2-7.4 (5H, m); (Z)-isomer showed vinylic
protons at δ 5.52 (d, J ) 11 Hz) and 5.78 (d, J ) 11 Hz); MS
m/z (rel intensity) 220 (M+, 30), 205 (30), 105 (100); HRMS
calcd for C14H20S 220.12857; found 220.12881]. Elution with
light petroleum ether/diethyl ether 90:10 gave (E)-3,3-dimeth-
ylbut-1-en-1-yl 2-cyanopropyl sulfide (32b) as an oil (35 mg,
10%) [1H NMR δ 1.05 (9H, s), 1.6 (6H, s), 6.05 (A part of an
AB system, J ) 15.2 Hz), 6.25 (B part, J ) 15.2 Hz); MS m/z
(rel intensity) 183 (M+, 15), 168 (20), 115 (60), 101 (50), 99
(50), 83 (60), 59 (100); HRMS calcd for C10H17NS 183.10817,
found 183.10805].
F r om 2-(Eth oxyca r bon yl)eth a n eth iol (2). Elution with
light petroleum ether gave a 97:3 (E,E)/(E,Z) mixture of bis-
(3,3-dimethylbut-1-en-1-yl) sulfide (28b) (165 mg, 42%) and
an ca. 85:15 (E)/(Z) mixture of 3,3-dimethylbut-1-en-1-yl
2-(ethoxycarbonyl)ethyl sulfide (17b) (120 mg, 28%) [1H NMR
δ (200 MHz) 1.0 (7.65H, s), 1.11 (1.35H, s), 1.27 (3H, t, J )
7.5 Hz), 2.6 (2H, t, J ) 7.0 Hz), 2.88 (2H, t, J ) 7.0 Hz), 4.15

1,5-Radical Translocation Reaction
J . Org. Chem., Vol. 61, No. 20, 1996 6789
Hz), 7.2-7.6 (5H, m); MS m/z (rel intensity) 236 (M+, 20), 195
(30), 132 (50), 105 (100), 73 (80). Anal. Calcd for C13H20SSi:
C, 66.04; H, 8.53; S, 13.56, Si, 11.88. Found: C, 66.24; H, 8.57;
S, 13.50].
Rea ction of P h en eth yl Th iol 1 w ith 1-P h en ylp r op yn e.
Chromatography gave 2,5-dimethyl-3,4-diphenyl-2,3-dihy-
drothiophene (30g) (100 mg, 19%), mp 84-85 °C [1H NMR δ
(200 MHz) 1.0 (3H, d, J ) 7 Hz), 2.15 (3H, s), 4.25 (1H, A part
of an AB system, J ) 7 Hz), 4.40 (1H, B part of an ABX3
system, five lines, J AB ) J BX ) 7 Hz), 7.0-7.4 (10H, m); MS
m/z (rel intensity) 266 (M+, 100), 251 (100), 189 (55). Anal.
Calcd for C18H18S: C, 81.15; H, 6.81; S, 12.04. Found: C,
81.40; H, 6.84; S, 11.98] and a 2:1 inseparable mixture of 30g
and phenethyl 1-phenylpropen-1-yl sulfide (16g) (E/Z mixture)
(290 mg, 56% overall yield) [16g: 1H NMR δ (200 MHz) 2.25
(3H, s), 2.80-3.10 (4H, m), 6.40 (0.25H, s), 6.50 (0.75H, s), and
aromatic protons; GC/MS m/z (rel intensity) 254 (M+, 30), 150
(100), 135 (30), 129 (50), 115 (40), 105 (50)].
Rea ction of P h en eth yl Th iol 1 w ith Oct-4-yn e. Chro-
matography gave a 3:2 mixture of bis(oct-4-en-1-yl) sulfide
(28e) [isomeric mixture] and tetrapropylthiophene 31e (35 mg,
7% overall yield) [1H NMR δ (200 MHz) 0.8-1.0 (12H, m), 1.3-
1.7 (8H, m), 2.0-2.2 and 2.2-2.3 (4.8H, m, 28e allylic
methylenes), 2.38 (0.8H, t, J ) 7.5 Hz, collapsing to singlet
upon irradiation at δ 1.5; 31e thienylic methylene), 2.62 (0.8H,
t, J ) 7.5 Hz, collapsing to singlet upon irradiation at δ 2.07;
31e thienylic methylene), 5.5-5.8 [0.6H, ninylic protons;
triplets of comparable intensity with J ) 7.0 Hz are present
at δ 5.54 (collapsing to singlet upon irradiation at δ 2.07), 5.65
(collapsing to singlet upon irradiation at δ 2.07), 5.68 (collaps-
ing to singlet upon irradiation at δ 2.3), and 5.75 (collapsing
to singlet upon irradiation at δ 2.3)]; GC/MS m/z (rel intensity)
28e 254 (M+, 30), 225 (70), 211 (100); 31e 252 (M+, 15) and
223 (100)] and a 70:30 (Z)/(E) mixture of oct-4-en-1-yl phen-
ethyl sulfide (16e) (300 mg, 60%) [1H NMR δ (200 MHz) 0.85-
0.95 (6H, m), 1.3-1.55 (4H, m), 2-2.25 (4H, m), 2.8 (2.8H, br
s), 2.85 (1.2H, br s), 5.42 (0.3H, t, J ) 7 Hz), 5.64 (0.7H, J )
7 Hz), 7.15-7.35 (5H, m); MS m/z (rel intensity) 248 (M+, 15),
144 (30), 143 (30), 105 (100). Anal. Calcd for C16H24S: C,
77.36; H, 9.74; S, 12.91. Found: C, 77.60; H, 9.80; S, 12.85]
Ack n ow led gm en t. This work has been carried out
in the frame of the Progetto di Finanziamento Triennale
Ateneo di Bologna. We also acknowledge financial
support from the Ministero dell’Universita` e della
Ricerca Scientifica e Tecnologica (MURST) and CNR
(Rome).
J O960279V