The synthesis of ethenyl bifunctional reagents containing a sulfone moiety and zirconium by the abnormal addition of Cp2Zr(H)Cl to internal acetylenic sulfones

Article abstract of DOI:10.1039/a904620h

Ethenyl bifunctional reagents containing a sulfone moiety and zirconium are prepared by the abnormal addition of Cp₂Zr(H)Cl to internal acetylenic sulfones.

Full text of DOI:10.1039/a904620h

The synthesis of ethenyl bifunctional reagents containing a sulfone moiety and
zirconium by the abnormal addition of Cp2Zr(H)Cl to internal acetylenic
sulfones
Xian Huang* and De-Hui Duan
Department of Chemistry, Zhejiang University (Xixi Campus), Hangzhou Zhejiang 310028, P.R. China.
E-mail: Huangx@mail.hz.zj.cn
Received (in Cambridge, UK) 9th June 1999, Accepted 27th July 1999
Ethenyl bifunctional reagents containing a sulfone moiety
and zirconium are prepared by the abnormal addition of
Cp2Zr(H)Cl to internal acetylenic sulfones.
Hex-1-ynyl p-tolyl sulfone was synthesized in two steps
according to the method of Truce.12 After hydrozirconation–
hydrolysis, a mixture of E and Z vinyl sulfones (E+Z = 2.9+1)
1
was obtained (Scheme 2). Its H NMR spectrum (300 MHz)
Acetylenic sulfones have been used extensively in organic
synthesis as activated acetylene equivalents. They can take part
in cycloadditions,1 Michael additions2 and alkylative desulfo-
nylation reactions.3 Surprisingly, little attention has been paid to
their hydrometalation reactions. On the other hand, via the
hydrozirconation of alkynes, many bifunctional ethenyl rea-
gents have been synthesized containing elements such as
selenium and zirconium,4 tellurium and zirconium,5 silicon and
zirconium,6 tin and zirconium,7 zinc and zirconium8 and boron
and zirconium.9 Apparently, no efforts have been focused on the
bifunctional ethenyl reagent containing sulfur and zirconium.
We now report that we have successfully synthesized sulfonyl-
substituted alkenylzirconocene compounds via the hydro-
zirconation of internal acetylenic sulfones. Unexpectedly, the
products of anti-addition of Cp2Zr(H)Cl to the acetylene are
observed.
Phenylacetylenic sulfones 1a–c were synthesized in good
yields according to the method of Suzuki.10 Hydrozirconation
of the acetylenic sulfones with 1.2 equiv. of Cp2Zr(H)Cl in THF
for 5 min at room temperature gave a clear yellow solution.
Unique E-vinyl sulfones 3a–c or E-b-deuterovinyl sulfones 4a–
c were obtained respectively after hydrolysis or deuterolysis
(Scheme 1 and Table 1).† The E-olefin geometry was verified
by the coupling constant (3JHH = 15.4 Hz) of the vicinal
olefinic protons. In addition, the product melting points are also
identical to those previously reported.11 The olefinic proton of
every deuterovinyl sulfone presents a single peak at d 6.84,
which shows that the deuterium atom must be attached to the b-
position of the sulfonyl group. Thus the (Z)-b-sulfonylalk-
enylzirconocene compounds 2 are produced in the hydro-
zirconation reaction (Scheme 1).
exhibits a doublet of triplets at d 6.97 (E-Hb, J 15.1, 6.8 Hz) and
multiple peaks at d 6.20–6.32 [including E-Ha, (dt, J 15.1, 1.4
Hz) and Z-Ha + Hb (ABX2 system, JAB 11.1 Hz, JAX 6.5 Hz)].
1
Further proof is also provided by the H NMR signals for two
kinds of methylenic protons [d 2.67 (q, 0.52 H, J 7.7, 6.5 Hz, Z-
CH2) and 2.25 (dq, 1.48 H, J 7.4, 6.8, 1.4 Hz, E-CH2)]. The
proportion of the E+Z mixture was estimated via the integral
areas of the two kinds of methylenic protons. After the parallel
experiment of hydrozirconation–deuterolysis, a mixture of two
regio- and stereo-isomers (E+Z = 3+1 by 1H NMR) was
obtained (Scheme 2). Its 1H NMR spectrum exhibits a triplet at
d 6.97 (E-Hb), a single peak at d 6.26 (Z-Ha), a triplet at d 2.68
(Z-CH2) and a quartet at d 2.25 (E-CH2). These results show that
two types of alkenylzirconocene compounds 2d (I and II) are
generated in the hydrozirconation reaction.
Compounds 2 were reacted with various electrophiles (Table
2). NCS, NBS and I2 (2.5 equiv.) reacted with 2a to give b-halo
vinyl sulfones. Using the method, we can access Z-b-halo vinyl
sulfones, whose configurations were identified by comparisons
with authoritative data.13 Thus this approach complements the
addition of sulfonyl halides to acetylenes, which provides either
an E and Z mixture13 or only the E isomer.12 Carbon–carbon
bond formation also occurred readily with various carbon
electrophiles. Reactions with carboxylic acid chlorides afforded
(Z)-b-sulfonyl a,b-unsaturated ketones. The cross-coupling
with allyl bromide provided (E)-penta-1,4-dienyl sulfone. Their
configurations were affirmed by H–H 2D NOSEY spectra (300
MHz). As is expected, the reaction of 2d with BzCl afforded
two isomers.
There are some regiochemical and stereochemical issues
associated with the addition of Cp2Zr(H)Cl across unsymme-
trical acetylenic sulfones. Based on the different substituents
(Bu or Ph) on the acetylene bond, a- (major) or b-sulfonyl
alkenylzirconocene compounds are obtained respectively. The
different regiochemistry could be ascribable to the dissimilarity
of the polarizing ability of the two groups to the C·C triple bond
and the long-distance p,p-interaction of the phenyl and
bicyclopentadienyl groups.
Scheme 1
Table 1 Yields and melting points for 3a–c and 4a–c
Compound
Ar
Yield (%)a
Mp/°C
3a
3b
3c
4a
4b
4c
Ph
72
69
70
70
73
68
74.5–75.5
126–121
82–84
73.5–75
118–120
82–83
p-Tol
p-ClC6H4
Ph
p-Tol
p-ClC6H4
a Yields of pure compounds.
Scheme 2
Chem. Commun., 1999, 1741–1742
1741

Table 2 Reaction of 2a and 2d with electrophiles
Project 29772007 is supported by the National Natural
Science Foundation of China; this work is also supported by the
Laboratory of Organometallic Chemistry, Shanghai Instituted
of Organic Chemistry, Academia Sinica.
Isolated
yield (%)
2
E–X
Product
Notes and references
†All new compounds were characterized via IR, 1H NMR (300 MHz), EI-
MS and elemental analysis.
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a Reaction conditions: CuBr (0.5 equiv.), acid chlorides (1.05 equiv.), THF,
25 °C, 2 h. b Reaction conditions: Pd(PPh3)4 (5 mol%), allyl bromide (1.05
equiv.), 40 °C, 3 h.
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In conclusion, bifunctional ethenyl reagents containing
sulfone and zirconium moieties are prepared by the abnormal
addition of Cp2Zr(H)Cl to internal acetylenic sulfones. The
addition reactions usually generate vinyl sulfone compounds,
which can be exploited for further synthetic elaboration.14
Currently a more thorough study is being carried out in our
laboratory.
Communication 9/04620H
1742
Chem. Commun., 1999, 1741–1742