A Highly Selective Synthesis of Versatile (E)-1-Phenylthio Vinylstannanes

Article abstract of DOI:10.1016/S0040-4039(00)93424-5

An efficient, palladium-catalyzed hydrostannation of 1-phenylthio-1-alkynes 1 is described.This novel tributyltin hydride addition provides versatile 1-phenylthio vinylstannanes 2 regio- and stereoselectively.Key Words: Hydrostannylation; Palladium(0); Tr

Full text of DOI:10.1016/S0040-4039(00)93424-5

'Te~ahedron Letters, Vo1.32, No.38, pp 5047-5050, 1991
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Pergamon Press pie
A Highly Selective Synthesis of Versatile
(E)- 1-Phenylthio. Vinylstannanesl
Plato A. Magriotis,* John T. Brown,2 and Mary E. Scott
Department ofChemistry, West Virginia University, Morgantown, WV 26506
Key Words: Hydrostannation; Palladium(O); Tributyltin Hydride; 1-Phenylthio-l-alkynes; (E)-l-Phenylthio Vinylstannanes
Abstract: An efficient, palladium-catalyzed hydrostannation of 1-phenylthio-l-alkynes 1 is described. This novel
tributyltin hydride addition provides versatile 1-phenylthio vinylstannanes 2 regio- and stereoselectively.
In connection with several projects currently under investigation in our laboratory, we required a fast and
general route to a variety of 1-phenylthio vinylstannanes such as 2a, 2b, 2c, 2d, and 2e. The importance of
PhS
.SnBu3
P h S - - C ~ C m R
1
a, R = CH2OSiMe2tBu
H
OSIMe2tBu
PhS/~__~R
b, R = CH2OH
S
~
c, R=CH3
Ph
OSiMe2tBu
d, R = CH(OH)CH2OSiMeztBu
Bu3Sn
H
e, R = CH2OCH2CON(OCH3)CH 3
H
"SnBu3
2
4
both vinyl sulfides3 and vinylstannanes4 as useful synthetic intermediates provided an additional incentive for
the stereoselective construction of these previously unknown olefins.
Early experimentation focusing on application of various tributylstannyl-radical addition protocols to la
resulted either in regioisomer 3 as the major product5 or in variable composition mixtures of 3 and 4 with 4
predominating.6 In light of these results we turned our attention to hydrostannation reactions of la that would
proceed by a polar mechanism and therefore were likely to provide the desired regioisomer 2a. Consequently,
we have recently described a stannylcuprate addition to la producing 2a in 65% yield.11
Pursuing the development of a more convenient and efficient access to 2, we set out to examine the
palladium-catalyzed hydrostannation12 of 1-phenylthio-l-alkynes L We now report that this process is highly
regio- and stereoselective affording 1-phenylthio vinylstannanes 2 in very good yields (Table 1).13 For most of
the entries in Table I only a trace amount of regioisomeric products such as 4 (for entry 1) could be detected
(>20:1) by the analytical methods employed.14 The complete stereoselectivity observed was established to be
5047

5048
syn by consideration of tin-vinylic hydrogen coupling constants in the 1H NMR spectra of products 2 (average
value -50 Hz, cis Snll7/Snll9).15 Catalysis by Pd(0) seems to be extremely efficient (1 tool% or less) since a
control reaction of la and Bu3SnH (benzene; 23°C, 48h) was found to be very slow giving rise to a mixture of
2a, 3, and 4 (-35% overall yield) presumably by both polar and free-radical mechanisms.
In a general procedure, the 1-phenylthio-1-alkyne 1 (5.0 mmol) was weighed into a flame-dried, round-
bottomed flask and dissolved in benzene (20 ml, distilled from sodium benzophenone ketyl) under argon (23°(2).
To the resulting solution was added tetrakis(triphenylphosphine)palladium(0) (0.05 mmol, 58 mg) rapidly,
followed by tributyltin hydride (neat, dropwise via syringe; 1.05 equiv, 5.25 mmol, 1.4 ml). After a few
minutes complete conversion to a single, less polar product was detected by sg TLC (15% benzene in hexane).
Benzene was removed on a rotary evaporator and the oily residue was purified by sg filtration using hexane as
the initial during solvent (75-90% yields).
Examination of entry 6 (Table I) reveals that the parent 1-phenylthio vinylstannane 2f can be efficiently
synthesized without recourse to t~-lithiation of phenyl vinyl sulfide.16 Comparison of products 2g17 and 2h
(entries 7 and 8) with vinylstannanes 5 and 6 produced by Pd(0)-catalyzed hydrostannation of 3-decyne-2-
onel2c,d and 1-phenyl-1-propynel2b,c respectively, points out the strong regiochemical control exerted by sulfur
induced polarization in alkynyl sulfides 1. More direct evidence for this electronic effect was obtained by
÷o-
+ f
tBu
0
PhS~j._OSiMe2tBu
B u 3 S n ~ H
P h S O~ -- - O S i M e2
CH3(CH2)4CH2H ~ CSHnBu33
H
SnBu3
5
7
8
6
9
a, R = CH~OSiMe2tBu
b, R = CH2OH
1 0
hydrostannation of the sulfoxide corresponding to la which gave rise to both regioisomers 7 and 8 in a 2:1 ratio
(80% yield). 18 Preliminary results suggest that similar levels of regio- and stereoselectivity can be expected
from the Pd(0)-catalyzed hydrostannation of 1-phenylseleno-l-alkynes 9. Specifically, alkynyl selenides 9a
and 9b were found to yield (E)-1-phenylseleno vinylstannanes 10a and 10b almost exclusively (75% isolated
yield).
In conclusion, the procedure reported herein by virtue of its wide scope and combination with the facile
transmetallation of vinylstannanes, constitutes a very attractive alternative to the sometimes inconvenient and
inconsistent a-lithiationl5,19 as the means toward the synthesis of functionalized vinyl sulfides. Work is in
progress on the application of stannanes 2 and 10 to the synthesis of wisubstituted olefins as well as other
interesting target molecules.
Acknowledgement
Financial support from the American Cancer Society (Research Grant #CH-496 and
Institutional Grant #IN-181) and the donors of the Petroleum Research Fund administered by the American
Chemical Society (2081 l-G1) is gratefully acknowledged. We also thank the National Science Foundation
(CHE-8913626) for an instrumentation grant (GC/MS system).

5049
T a b l e
E n t r y
I
P h e n y l t h i o a l k y n e a
V i n y l s t a n n a n eb
% Yieldc
PhS~.~/'- OSiMe2tBu
1.
PhS -- XOSiMe2te.
BuaS,,~-~H
90
la
2a
P h ~ T ~ HOH
BuaS 2b
84
2.
PhS
~
\
lb OH
3.
PhS --- Me
P h S ~Me
79 d
I
c
Bu3Sn" 2/H
",
OH
PhS
"
O.
4.
5.
PhS ~d ~...OSiMe2tau
Bu3S2~d~OSiMe2tBu
80
90
PhS le O~..OCH3
oN*'cH3
P h S s O "~ ,OCH3
Bu3Sn
H 0"" N
2e
"CH3
PhS
6.
P h S - -
~ .
87
Bu3Sn"
1
f
O
O
7.
PhS-~'--~
Ph S ~ , ) ~ ,
BuaSn
88
H
OSiMe2tBu
l g OSiMe2tBu
2g
8.
PhS - - Ph
PhSxr.~_('Ph
75 d
l h
BuaSn 2h H
9.
PhS----~=---Bu
1i
PhS).~.~Bu
BuaSn~
82d
85
H
2i
PhS~p_~/SiMe3
u sn"
10.
PhS --- SiMe3
.
2j
lj
B
aphenylthioacetylene (1t') was synthesized from phenyl vinyl sulfide by a two-pot, three-step procedure involving bromination-
dehydrobromination and NaNH2/NH3 elimination (Magriotis, P. A.; Brown, J. T., submitted for checking to Org. Synth.).
Phenylthioalkynes ld and lh were prepared by Luehe reduction of lg and reaction of TMS phenylacetylene with phenyl disulfide
(CuOTf, CaCO3, THF-dioxane; 80°C, 2h)20 respectively, bAll vinylstannane products exhibited spectral properties (1H NMR, IR,
and GC/MS) in accord with the assigned structures. The rcgiochemical outcome of entry 8 was confLrmed by inspection of the
methyl group signal (IH NMR; doublet, J = 1.8 Hz) of a 2h derivative obtained by the following sequence: (1) Iransmetallation (n-
BuLi, TI-IF; -30°(2, 0.5h) and reaction with hexanal; (2) protection (MOM-CI, CH2Cl2, diisopropylethylamine; 23°C, 5h); and (3)
Ni(0)-catalyzed coupling of the vinyl sulfide with MeMgBr (toluene, 110°C).3d Regiochemical assignment of entry 9 was made by
analogy and literature data on the hydrostannafion of 1-1rimethylsilyl-l-alkynes.12a,c eIsolated yield after preparative TLC or sg
flash chromatography, dRegioselectivity: 2c -19:1 (GC/MS); 2h -15:1 (1H NMR); 2i -18:1 (GC/MS).

5050
References and Notes
1.
2.
3.
Presented at the 32nd National Organic Chemistry Symposium of the American Chemical Society,
Minneapolis, Minnesota, June 16-20, 1991.
Recipient of the ACS Division of Organic Chemistry Travel Award Program for Outstanding
Undergraduate Students (Atlanta National Meeting, April 1991) sponsored by Johnson & Johnson.
(a) Vermeer, P.; Meijer, J.; Eylander, C.; Brandsma, L. Recl. Trav. Chim. Pays-Bas 1976, 95, 25. (b)
Trost, B. M.; Lavoie, A. C. J. Am. Chem. Soc. 1983, 105, 5075 and references cited therein. (c)
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This was accomplished by tdethylborane7- or diisobutylaluminum hydride8-catalyzed hydrostannation of
la (23°C). The application of these reactions to other 1-phenylthioalkynes will be reported in due course.
The most synthetically useful ratio of 3:4 was 1:5 and obtained under the conditions reported by Corey9a
and Jung9b (1.3 equiv Bu3SnH, 95°C, cat. AIBN). These results are consistent with a free radical
mechanism, l0 involving anti addition of Bu3SnH followed by isomerization of 3 to the apparently more
stable 4.
4.
5.
6.
7.
8.
Nozaki, K.; Oshima, K.; Utimoto, K. Tetrahedron, 1989, 45, 923.
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13. The requisite 1-phenylthio-1-alkynes 1 were prepared by reaction of lithium phenylthioacetylide with the
appropriate electrophile. Experimental details of these syntheses will be published elsewhere. It is noted
that iododestannylation of vinylstannanes 2 proceeded smoothly (90-95% yields of vinyl iodides).
14. GC (HP 5890 Series II)-MS (HP 5970 Mass Selective Detector) equipped with an HP-1 column (50m,
0.2mm ID) and 1H NMR (Jeol GX 270 MHz). Similar regioselectivity was observed in the hydroboration
of li, see: Hoshi, M.; Masuda, Y.; Arase, A. Bull. Chem. Soc. Jpn. 1990, 63,447.
15. For comparison, the average trans coupling constant of Sn 117/Snll9-vinylic hydrogen in 3 is -190 Hz.
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18. Interestingly, hydrostannation of the sulfone gave rise to approximately a 1:1 mixture of regioisomers.
Under palladium catalysis, 1-chloro-l-octyne has been reported to consume 1 equiv of tributyltin hydride
furnishing (E)- 1-chloro- 1-wibutylstannyl- 1-octene exclusively.12c
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(Received in USA 14 June 1991)