Yttrium-mediated conversion of vinyl grignard reagent to a 1,2-dimetalated ethane and its synthetic application

Article abstract of DOI:10.1021/ja077992u

A new 1,2-dimetalated ethane was generated from a vinyl Grignard reagent in the presence of yttrium(III) chloride, sodium cyclopentadienide, and diisobutylaluminum hydride (Dibal). This reagent enables the regio- and stereoselective (metaloethyl)metalation of acetylenes to produce ethylated alkenes after hydrolysis. In addition to simple hydrolysis, further carbon-carbon bond formation or functionalization at the metaloethyl group is possible, demonstrating that the yttrium-based 1,2-dimetalated ethane works as a conjunctive reagent. In addition, the reactive dicarbanionic character of this reagent effects one-pot synthesis of cyclopronanols from esters via consecutive double carbonyl addition. Copyright

Full text of DOI:10.1021/ja077992u

Published on Web 02/19/2008
Yttrium-Mediated Conversion of Vinyl Grignard Reagent to a 1,2-Dimetalated
Ethane and Its Synthetic Application
Ryoichi Tanaka, Hiroaki Sanjiki, and Hirokazu Urabe*
Department of Biomolecular Engineering, Graduate School of Bioscience and Biotechnology, Tokyo Institute of
Technology, 4259-B-59 Nagatsuta-cho, Midori-ku, Yokohama, Kanagawa 226-8501, Japan
Received October 18, 2007; E-mail: hurabe@bio.titech.ac.jp
Chart 1. Products Obtained from Acetylenes According to
Among the lanthanide reagents used to mediate organic reac-
tions,1 yttrium reagents are used for hydroyttration,2 hydrosilylation,3
and hydroamination4 of alkenes and alkynes and show a preference
for interaction with carbon-carbon multiple bonds. Here we report
that an yttrium reagent can react even with a metalated alkene such
as a vinyl Grignard reagent, leading to a new method of generating
1,2-dimetalated ethane 1 (Scheme 1). As there are still limitations
in the practical generation of 1,2-dimetalated ethane,5-7 a funda-
mental dicarbanionic species and a versatile conjunctive reagent,6,7
we also demonstrate some synthetic applications of 1 according to
Scheme 1.
Scheme 2
Scheme 1. Yttrium-Mediated Generation of 1 and Its Application
Scheme 3. Utility of 1 as Conjunctive Reagent
Yttrium(III) chloride was first treated with sodium cyclopenta-
dienide to produce yttrium dichloride 2,8 to which diisobutylalu-
minum hydride (Dibal), vinylmagnesium chloride, and 5-decyne
(5) were added in this order (Scheme 2). The reaction most likely
proceeded via (i) generation of yttrium hydride 3 from 2 and (ii)
hydroyttration of the vinyl Grignard reagent to give 4 (i.e., 1 via
metal exchange). Finally, the carbometalation of the acetylene 5
with 1 afforded ethylated alkene 7 in 98% yield with virtually
complete stereoselectivity after hydrolytic workup.9 Other lanthanide
trichlorides such as Sm, Sc, Ce, and La in place of Y did not
promote this reaction (yield of 7: 29%, 15%, trace, and trace,
respectively). Deuteriolysis of the above reaction mixture produced
dideuterated product 7-d2, confirming the presence of a bismetalated
intermediate 6. Additional products obtained by this reaction are
summarized in Chart 1 (dotted line refers to ethylated position),
which shows that the carbometalation proceeded in a regio- and
stereoselective manner, always producing single trisubstituted
olefins 8-13.10
ments). While bromination of 15 (generated from acetylene 14)
with CBr4 or Br2 selectively afforded monobromide 16 or 17,11
respectively, combination of these brominating agents or solely CBr4
in the presence of a copper catalyst afforded dibromide 18. Copper-
catalyzed allylation of 15 cleanly produced 19, and the successive
applications of the above bromination and this allylation achieved
a four-component coupling process to produce 20. Two more
examples are shown in Scheme 3, which include dibromination or
a palladium-catalyzed selective monoalkenylation of the intermedi-
ates generated from each acetylene 5 or 22 to give 21 or 23,
respectively.
Scheme 2. Yttrium-Mediated (â-Metaloethyl)metalation of
Acetylenes
Although ethylene complexes of group 4 metals, such as 25 (M
) Ti or Zr with appropriate ligands),7 are known to constitute a
practical and synthetically useful 1,2-dimetalated ethane, these
Scheme 3 illustrates the utility of 1 as a conjunctive reagent
(dotted lines indicate the ethylene basement and two other frag-
9
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J. AM. CHEM. SOC. 2008, 130, 2904-2905
10.1021/ja077992u CCC: $40.75 © 2008 American Chemical Society

C O M M U N I C A T I O N S
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species usually work as metal transfer reagents toward 1,6-enynes
24 to allow intramolecular cyclization, producing 27 via metalacycle
26,7,12,13 instead of (â-metaloethyl)metalation (eq 1). In contrast,
with the newly developed reagent 1, 1,6-enyne 28 underwent clean
(â-metaloethyl)metalation to give 29 unaccompanied by the cyclized
product 30 (eq 2).
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To confirm the nucleophilic nature of this reagent, we investi-
gated its reaction with an electrophile. Actually the reagent 1
underwent double addition to ethyl decanoate to produce 1-nonyl-
1-cyclopropanol in one pot, albeit in a low product yield around
20%. After some tuning of its reagent composition,10 yttrium-based
reagent 1 gained improved product yields as shown in eq 3. Even
the R,â-olefinic and -acetylenic esters 31c-e afforded cyclopro-
panols 32c-e uniformly in satisfactory yields, which is not
attainable with the aforementioned 1,2-dimetalated ethane 25.14
Similarly, the reagent 1 and 5-alkenoate 33 cleanly afforded 34,
without contamination with 35 that is usually observed in the
reaction with 25.14
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(9) The reagent 1 that had been stored under argon for one day at room
temperature did not give the product 7 upon reaction with 5. Attempted
generation of 1,2-dimetalated propane from (E)- or (Z)-1-propenylmag-
nesium bromide and its addition to 5 are so far unsuccessful.
(10) For experimental details, see the Supporting Information.
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In summary, a 1,2-dimetalated ethane was conveniently generated
by an yttrium-based multimetallic reagent system. It has new
characteristics that are complementary to those of the existing 1,2-
dimetalated ethanes already used in organic synthesis. Further
synthetic applications are now under investigation.
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Acknowledgment. This work was supported, in part, by a
Grant-in-Aid for Scientific Research on Priority Area 16073208
from the Ministry of Education, Culture, Sports, Science and
Technology, Japan. R.T. thanks the Japan Society for the Promotion
of Science for a Research Fellowship for Young Scientists.
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100, 2797-2799. (b) de Meijere, A.; Kozhushkov, S. I.; Savchenko, A.
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These low yields most likely come from the metal transfer from 25 to the
carbon-carbon unsaturated bond of these substrates: (e) Urabe, H.;
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Supporting Information Available: Experimental procedures and
physical properties of products. This material is available free of charge
via the Internet at http://pubs.acs.org.
References
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